bmj open · 69 work schedules between the day and night (i.e., rotating shift work). previous...

For peer review only

Association of eating behaviors with diurnal preference and rotating shift work in Japanese female nurses: a cross-

sectional study

Journal: BMJ Open

Manuscript ID bmjopen-2016-011987

Article Type: Research

Date Submitted by the Author: 21-Mar-2016

Complete List of Authors: Yoshizaki, Takahiro; Toyo University, Faculty of Food and Nutritional Sciences Kawano, Yukari; Tokyo University of Agriculture, Department of Nutritional

Science, Faculty of Applied Bio-Science Noguchi, Osamu; Ome City General Hospital, Department of Gastroenterology Onishi, Junko; Ome City General Hospital, Department of Nursing Teramoto, Reiko; Ome City General Hospital, Department of Clinical Nutrition Sunami, Ayaka; Tokyo University of Agriculture, Graduate School of Agriculture Yokoyama, Yuri; Tokyo University of Agriculture, Graduate School of Agriculture Tada, Yuki; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science

Hida, Azumi; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science Togo, Fumiharu; The University of Tokyo, Graduate School of Education

<b>Primary Subject Heading</b>:

Nutrition and metabolism

Secondary Subject Heading: Epidemiology, Occupational and environmental medicine, Public health

Keywords: Dietary habits, Chronotype, Rotating shift worker, Diurnal preference

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1

Association of eating behaviors with diurnal preference and 1

rotating shift work in Japanese female nurses: a 2

cross-sectional study 3

4

Takahiro Yoshizaki1, Yukari Kawano

2, Osamu Noguchi

3, Junko Onishi

4, Reiko Teramoto

5, 5

Ayaka Sunami6, Yuri Yokoyama

6, Yuki Tada

2, Azumi Hida

2, Fumiharu Togo

7 6

7

1Faculty of Food and Nutritional Sciences, Toyo University, Gunma, Japan 8

2Department of Nutritional Science, Faculty of Applied Bio-Science, Tokyo University of 9

Agriculture, Tokyo, Japan 10

3Department of Gastroenterology, Ome City General Hospital, Tokyo, Japan 11

4Department of Nursing, Ome City General Hospital, Tokyo, Japan 12

5Department of Clinical Nutrition, Ome City General Hospital, Tokyo, Japan 13

6Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan 14

7Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo, 15

Tokyo, Japan 16

17

Running head: Rotating Shift Work and Eating Behaviors 18

Address correspondence to: 19

Takahiro Yoshizaki, Ph.D. 20

Faculty of Food and Nutritional Sciences, Toyo University 21

1-1-1 Izumino, Oura-gun, Itakura-machi, Gunma 374-0193, Japan 22

Tel: +81-276-82-9012 Fax: +81-276-82-9000 E-mail: [email protected] 23

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ABSTRACT 24

Objectives 25

Our study examines the relationships between work schedule and eating behaviors, and 26

considers whether diurnal preference could explain the relationship. 27

Methods 28

Japanese female nurses were studied (39 day workers and 123 rotating shift workers, aged 21–29

63) using self-administered questionnaires. The questionnaires assessed eating behaviors, 30

diurnal preference, and demographic characteristics. Sakata’s Eating Behavior Questionnaire 31

consists of 55 items, where higher scores signify higher probabilities of obesity, and was used 32

to obtain scores for the levels of obesity-related eating behaviors, including cognition of 33

constitution, motivation for eating, eating as a diversion, feeling of satiety, eating style, meal 34

contents, and temporal eating patterns. A Japanese version of the Morningness-Eveningness 35

questionnaire was used to measure self-rated preference for a morning activity pattern 36

(Morning-type) or evening activity pattern (Evening-type). 37

Results 38

The scores for meal contents and temporal eating patterns in rotating shift workers were 39

significantly higher than those in day workers. The ME-score of rotating shift workers was 40

significantly lower, indicating a tendency for more Evening types among rotating shift workers. 41

Multivariable linear regression analyses revealed that the correlation with the ME-score was 42

significantly negative for the score for temporal eating patterns and showed a negative 43

association with the score for meal contents at a trend level, while current work shift was not 44

significantly correlated with the scores. 45

Conclusions 46

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These results suggest that rotating shift work is associated with a more unbalanced diet and 47

abnormal temporal eating patterns and that the associations may be mediated and/or modulated 48

partly by diurnal preference. 49

50

Keywords: Dietary habits; Chronotype; Rotating shift worker 51

52

STRENGTHS and LIMITATIONS of THIS STUDY 53

・There are few studies that have clarified whether the difference of diurnal preference explains 54

changes in eating behaviors in rotating shift workers. 55

・The aim of the present study was to elucidate the association between rotating shift work and 56

obesity-related eating behaviors, considering the diurnal preference, among Japanese female 57

nurses. 58

・Rotating shift work was associated with a more unbalanced diet and abnormal temporal eating 59

patterns, and the associations may be mediated and/or modulated partly by being of the 60

Evening type. 61

・These findings have important implications for the development of novel strategies for 62

preventing excessive weight gain in rotating shift workers. 63

64

65

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1. INTRODUCTION 66

A super-aged society leads to an increase in the social demand for nurses in medical facilities. 67

Among them, health problems can be caused by severe working conditions such as shifting of 68

work schedules between the day and night ( i.e., rotating shift work). Previous studies have 69

suggested that rotating shift work is related to higher risks of health problems, including 70

obesity, increases in body mass index (BMI), and adiposity with abnormal metabolism, 71

compared with fixed day work. 1-3

One of the possible factors for increasing the risks of these 72

health problems in rotating shift workers is their altered eating behavior. 4 5

Our previous 73

studies demonstrated that female workers who engaged in rotating shift work consumed more 74

sugar-sweetened beverages and snacks than day workers, 6 7

and that the rate of subjects who 75

reported skipping breakfast almost everyday (80–100%) on days on the day shift was 76

significantly higher in rotating shift workers compared with day workers. 8 A recent study by 77

another group has also indicated unbalanced dietary intake, such as greater intake of fats and 78

oils and lower intake of vegetables, in rotating shift workers compared with day workers. 9 79

However, it is unclear which aspects of obesity-related eating behavior change in rotating shift 80

workers, and which factors contribute to the altered eating behaviors in rotating shift workers. 81

82

One plausible factor contributing to the altered eating behaviors in rotating shift workers is a 83

changed circadian rhythm. Our previous study revealed that rotating shift workers had a 84

significant phase delay in the 24-h rhythm of cardiac autonomic nervous system activity 85

compared with fixed day workers, 10

suggesting a phase delay of the circadian rhythm among 86

rotating shift workers. The endogenous circadian clocks, controlled by the master circadian 87

clock in the suprachiasmatic nuclei of the hypothalamus, play a significant role in regulating a 88

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number of circadian and daily physiological rhythms, including feeding behavior. 11

For 89

example, a human laboratory study showed that the circadian clock regulated hunger and 90

appetite independently of the fasting-feeding rhythm and the sleep-wake cycle, 12

indicating 91

that the phase delay of the circadian clock might modify the timing of eating. Moreover, a 92

recent study revealed that a late midpoint of nocturnal sleep was associated with increases in 93

energy intake from undesirable dietary contents such as alcoholic beverages, confectioneries, 94

fats and oils, and meats in individuals who did not engage in night shift work. 13

Despite these 95

available data, which suggest a possibility of a close association between eating behavior and 96

the circadian clock, there are few studies that have clarified whether the association explains 97


99

To investigate epidemiologically the phase of the circadian clock during daily life, individual 100

preference in the phase of the sleep-wake cycle (i.e. , diurnal preference or chronotype), which 101

may be different from the actual sleep-wake cycle during daily life, was assessed using the 102

Japanese version of the Morningness-Eveningness questionnaire by Torsvall and Akerstedt. 14

103

15 Diurnal preference (e.g., Evening type or Morning type) are attr ibuted to differences in the 104

phase of the circadian clock. 16

Therefore, the aim of the present study was to elucidate the 105

association between rotating shift work and obesity-related eating behaviors, considering the 106

diurnal preference, among Japanese female nurses. Dietary habits were investigated using 107

Sakata’s Eating Behavior Questionnaire, which is included in the Guidelines for the 108

management of obesity disease in Japan. 17

Characteristics of eating behavior among 109

overweight individuals were extracted from an interview survey and compiled to produce the 110

questionnaire. 18

Our hypothesis was that rotating shift workers would have obesity-related 111

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eating behaviors associated with meal contents (e.g., greater intake of specific nutrients) and 112

temporal eating patterns (e.g., skipping breakfast and/or late dinner), and that diurnal 113

preference would partially explain the associations between rotating shift work and 114

obesity-related eating behaviors. 115

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2. METHODS 116

2.1 Participants 117

The study population consisted of nurses working at a general hospital in the center of Ome 118

city. Ome city is located in the west side of the Tokyo metropolitan area and is the fifth 119

largest city in the metropolis. Urbanization and industrialization are present in the region of 120

the plain, while districts in the hilly area in the western region of the city have rural 121

populations. A total of 506 nurses were handed the questionnaires by the chief nursing officer 122

on each ward. The purpose of this study and data handling procedures were described in a 123

cover letter with the questionnaire. Agreement to participate in this study was assumed on the 124

basis of receipt of an anonymous questionnaire. A total of 218 nurses (43.1%; age 19–63 yr) 125

responded. Among them, 56 were excluded from the analysis because of missing data [age 126

(n=2), current work schedules (n=6), residential status (n=1), marital status (n=2), years of 127

experience as a rotating shift worker (n=23), smoking status (n=2), alcohol status (n=4), 128

number of night shifts in the previous month (n=6), and the questionnaire about diurnal 129

preference (n=13)]. Because the scoring method for the questionnaire about obesity-related 130

eating behavior was different for men and women, 19

we decided to exclude the small number 131

of data from male nurses (n=20). As a result, 162 female nurses (39 day workers and 123 132

shift workers) were analyzed. Their mean total duration of experience in their current job was 133

12.2 ± 10.3 [SD] yr. In this study, individuals who worked only a fixed day shift (09:00–134

18:00 h) were defined as “day workers”, and those who worked both day shifts and night shifts 135

(18:00–09:00 h) in a rotating shift system as “rotating shift workers”. All the study 136

procedures were reviewed and approved by the Ethics Committee at the Tokyo University of 137

Agriculture (No. 1111). 138

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139

2.2 Assessments 140

A cross-sectional study using self-administered questionnaires on demographic characteristics, 141

diurnal preference and eating behavior was conducted in the general hospital at the beginning 142

of September 2012. Completed questionnaires were returned within two weeks. 143

Demographic characteristics of the participants included in the questionnaire were the 144

following: age, height, weight, current work schedule, years of experience in the current job 145

and as a rotating shift worker, marital status, residential status, smoking status, alcohol status, 146

and the number of night shifts in the previous month. Body mass index (BMI) was calculated 147

on the basis of self-reported height and weight [weight / height2 (kg / m

2)]. A Japanese 148

version of the Morningness-Eveningness questionnaire by Torsvall and Akerstedt, of which the 149

internal reliability has been confirmed, was used to measure self-rated preference for activity 150

in the morning or the evening. 14 15

Based on seven items about daily sleep habits or preference 151

consisting of 0–3 Likert scales, the Morningness-Eveningness score (ME-score) was calculated 152

(range: 7–28 points). A lower ME-score indicates a tendency for a greater preference for 153

activity in the evening (Evening type), while a higher ME-score indicates a greater preference 154

for activity in the morning (Morning type). The data about habitual eating behavior over the 155

previous one month was obtained from the response to Sakata’s Eating Behavior Questionnaire, 156

17 20 which was developed to detect obesity-related eating behavior. The details of the 157

contents of the questionnaire have been shown in previous studies. 17 18 20

In brief, each of the 158

55 items on eating habits is rated on a four-point scale ranging from “strongly disagree” to 159

“strongly agree”. These items are classified into the scores for seven areas regarding 160

cognition of constitution (range: 6–24), motivation for eating (range: 9–36), eating as a 161

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diversion (range: 4–16), feeling of satiety (range: 6–24), eating style (range: 5–20), meal 162

contents (range: 7–28), and temporal eating patterns (range: 8–32). Higher scores indicate 163

more improper eating behavior in terms of a higher probability of obesity. 21

164

165

2.3 Statistical analysis 166

After the normal distr ibution of variables had been tested by Kolmogorov-Smirnov test, the 167

t-test or Mann–Whitney U test and the χ2 test or Fisher 's exact test were used for continuous 168

and categorical variables, respectively, to compare the difference in demographic 169

characteristics, ME-score, and the scores for eating behavior between day workers and rotating 170

shift workers. For categorical variables, residuals between the observed and expected 171

frequencies were standardized to determine cells which were statistically different from 172

expected values. Simple and multivariable linear regression analyses (model 1) were 173

performed with each score for eating behavior (meal contents or temporal eating patterns) as 174

dependent variables, and current work schedule (0 = day work, 1 = rotating shift work) and 175

ME-score (continuous, in points) as independent variables. The model was extended (model 176

2) using demographic characteristics of the participants for covariate adjustment: age 177

(continuous, in years), years of experience as a rotating shift worker (continuous, in years), 178

marital status (0 = married, 1 = unmarried or divorced), residential status (0 = living alone, 1 = 179

not living alone), smoking status (“Do you smoke?”; 0 = no, 1 = yes), alcohol status (“Do you 180

drink alcohol?”; 0 = no, 1 = yes), and the number of night shifts in the previous month 181

(continuous, in days). All statistical analyses were performed with an SPSS statistical 182

software package (IBM SPSS 22.0 for Windows, SPSS Japan). P values less than 0.05 were 183

considered statistically significant using two-tailed tests. 184

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3. RESULTS 185

The demographic characteristics of day workers and rotating shift workers are shown in Table 186

1. Age was significantly higher in day workers compared with rotating shift workers (p < 187

0.05). The years of experience in the current work schedule were significantly more in day 188

workers compared with rotating shift workers (p < 0.05). Marital status and residential status 189

were significantly associated with the current work schedule (p < 0.05). ME-score for 190

rotating shift workers was significantly lower compared with day workers (p < 0.05), 191

indicating a tendency for more Evening types among rotating shift workers compared with day 192

workers. This significant difference was not attenuated after controlling for age as a 193

confounding variable (data not shown). 194

195

Table 1 Demographic characteristics of day workers and rotating 196

shift workers 197

Day workers Shift workers

P values

n=39 n=123

Age† (years) 44.2 ± 10.9 34.7 ± 8.7 < 0.001

Height†a

(cm) 156.7 ± 5.6 157.5 ± 5.5 0.175

Weight†b

(kg) 53.4 ± 8.3 53.8 ± 8.9 0.784

BMI†c

(kg/m2) 21.7 ± 2.7 21.7 ± 3.5 0.676

ME-score†§

(points) 20.8 ± 3.3 17.1 ± 4.0 < 0.001

Years of experience

Current work† (years) 17.4 ± 12.0 10.6 ± 9.2 0.002

Rotating shift work† (years) 11.8 ± 10.7 9.7 ± 8.7 0.652

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Number of night shifts (day/month) 0.0 ± 0.0 7.6 ± 3.1 -

Marital status‡ Married 32 ( 82 )

* 50 ( 41 )

0.001

Unmarried or divorced 7 ( 18 ) 73 ( 59 ) *

Residential status‡ Living alone 3 ( 8 ) 33 ( 27 )

*

0.014

Not living alone 36 ( 92 ) * 90 ( 73 )

Smoking status Yes 4 ( 10 ) 17 ( 14 )

0.785

No 35 ( 90 ) 106 ( 86 )

Alcohol status‡ Yes 21 ( 54 ) 51 ( 41 )

0.198

No 18 ( 46 ) 72 ( 59 )

198

Values are means ± standard deviation or number (%). 199

BMI, body mass index; ME-score, Morningness-Eveningness score 200 †Mann-Whitney U test 201

‡χ

2 test or Fisher's exact test (When p < 0.05, standardized residuals were determined for each 202

cell.) 203 *p < 0.05 204

§A lower ME-score is indicative of the Evening type. 205

aShift workers, n=120

206

bShift workers, n=118

207

cShift workers, n=118

208

209

The obesity-related eating behaviors of day workers and rotating shift workers are shown in 210

Table 2. The scores for meal contents and temporal eating patterns significantly differed 211

between the groups (p < 0.05), indicating an unbalanced diet and more irregular timing of 212

meals among rotating shift workers compared with day workers. Scores for other eating 213

behaviors did not differ between the groups (p > 0.05). 214

215

216

Table 2 Scores for habitual eating behavior in day workers and 217

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rotating shift workers 218

Normal Day workers Shift workers

p values

(Ref. 32) n=39 n=123

Cognition of constitution†a

(points) 14 14.3 ± 3.4 13.6 ± 3.7 0.328

Motivation for eating‡b

(points) 18 19.5 ± 4.9 18.8 ± 5.6 0.384

Eating as a diversion‡c

(points) 7 7.4 ± 2.4 7.1 ± 2.9 0.310

Feeling of satiety‡ (points) 10 10.9 ± 3.1 11.3 ± 3.2 0.427

Eating style‡ (points) 9 9.8 ± 3.5 9.7 ± 3.6 0.629

Meal contents‡ (points) 12 13.9 ± 3.9 15.6 ± 4.5 0.045

Temporal eating patterns‡d

(points) 16 16.5 ± 4.5 19.5 ± 4.8 0.001

219

Values are means ± standard deviation. 220

Higher scores indicate more improper eating behavior in terms of a higher probability of 221

obesity: Cognition of weight and constitution, having false recognition of and assumptions 222

about reasons for weight gain; Motivation for eating, having behavioral factors which can 223

induce over-eating; Eating as a diversion, being subject to psychological factors which increase 224

appetite (i.e., perceived mental stress); Feeling of satiety, being prone to have an appetite and 225

to eat as much as possible; Eating style, being prone to eat fast; Meal contents, having a 226

preference for a high fat diet and sweets (e.g., confectioneries and sweet buns); Temporal 227

eating patterns, irregularity of timing and number of meals taken during the day and delay in 228

timing of meals. 229 †t-test 230

‡Mann-Whitney U test 231


232


233

cDay workers, n=38

234

dShift workers, n=119

235

236

We examined the relationship between rotating shift work, ME-score, and scores for meal 237

contents and temporal eating patterns using simple and multivariable linear regression analyses. 238

Simple linear regression analyses (Table 3) showed that rotating shift work and a lower 239

ME-score were significantly (p < 0.05) associated with higher scores for meal contents and 240

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temporal eating patterns. Multivariable linear regression analyses (model 1) showed that the 241

ME-score was significantly (p < 0.05) associated with the score for meal contents, while the 242

effect of rotating shift work was attenuated to trend level (p < 0.1). Regarding temporal 243

eating patterns, the ME-score was significantly (p < 0.05) associated with the score, while 244

rotating shift work was not. In model 2, in which the variables of demographic characteristics 245

which significantly (p < 0.05) differed between the groups (i.e., age, years of experience as a 246

rotating shift worker, marital status, residential status, and number of night shifts per month) 247

and smoking and alcohol status were controlled, the correlations with the ME-score decreased 248

slightly but remained significantly negative (β = —0.329, p < 0.001) for temporal eating 249

patterns or at a trend level (β = —0.161, p = 0.082) for meal contents. 250

251

Table 3 Association of current shift schedule (rotating shift work) 252

and diurnal preference with scores for meal contents and temporal 253

eating patterns in multivariable linear regression models 254

Independent

variables

Unstandardized

coefficients

Standardized

coefficients p values

B SE β

Meal contents

Crude

Rotating shift work 1.689 0.804 0.164 0.037

ME-score —0.223 0.082 —0.210 0.007

Model 1


ME-score —0.183 0.089 —0.172 0.041

Model 2a


ME-score —0.171 0.098 —0.161 0.082

Temporal eating patterns

Crude

Rotating shift work 3.211 0.867 0.284 < 0.001

ME-score —0.465 0.086 —0.397 < 0.001

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Model 1


ME-score —0.395 0.093 —0.338 < 0.001

Model 2a


ME-score —0.384 0.101 —0.329 < 0.001 255 aAdjusted by age, years of experience as a rotating shift worker, marital status, residential 256

status, smoking status, alcohol status, and number of night shifts per month. Years of 257

experience in the current work schedule were not included in Model 2 because of a high level 258

of multicollinearity (Variance inflation factor = 8.101). 259

260

261

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4. DISCUSSION 262

Our cross-sectional study explored the association between rotating shift work and 263

obesity-related eating behaviors, considering diurnal preference, among Japanese female 264

nurses. As a result, the scores for meal contents and temporal eating patterns in rotating shift 265

workers were significantly higher than those in day workers. The ME-score of rotating shift 266

workers was significantly (p < 0.05) lower compared with day workers, indicating a tendency 267

for more Evening types among rotating shift workers. Multivariable linear regression 268

analyses revealed that the correlation with the ME-score was significantly negative (β = —269

0.329, p < 0.001) for the score for temporal eating patterns and showed a negative association 270

with the score for meal contents at a trend level (β = —0.161, p = 0.082), while current work 271

shift (i.e., rotating shift work) was not significantly correlated with the scores. These results 272

suggest that rotating shift work is associated with a more unbalanced diet and abnormal 273

temporal eating patterns and that the associations may be mediated and/or modulated partly by 274

diurnal preference (e.g. the Evening type). To the best of our knowledge, this is the first 275

study to show the associations between rotating shift work, diurnal preference, and eating 276

behavior. 277

278

Given the fact that the Evening type closely correlates with delays in the phase angle of the 279

circadian rhythm 16

and that the phase delay can be caused by light exposure and sleep/dark 280

schedules during nights on the days of the night shift, 22

our study indicates that being of the 281

Evening type, or the phase delay of the circadian rhythm, may correlate with altered eating 282

behavior in rotating shift workers. This indication is supported by previous studies. 10 23

For 283

example, one previous study revealed that rotating shift workers showed a phase delay in the 284

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circadian rhythm compared with day workers. 10

In addition, rotating shift workers have a 285

tendency for more Evening types compared with day workers, 8 24

which is consistent with our 286

results. We also demonstrated that a greater phase delay of the circadian rhythm was 287

associated with a later timing of breakfast among rotating shift workers. 23

However, causality 288

between diurnal preference or phase angle of the circadian rhythm and altered eating behavior 289

could not be examined, although these may have interactive effects. It should be explored in 290

future studies whether changes from the Evening type to the Morning type in diurnal 291

preference or the phase advance of the circadian rhythm would improve eating behavior in 292

rotating shift workers. 293

294

Our results show that rotating shift work is associated with higher scores for meal contents and 295

temporal eating patterns. A higher score for meal contents represents a greater preference for 296

a high-fat diet and sweets (e.g., confectioneries and sweet buns). 17 20

A higher score for 297

temporal eating patterns represents a greater irregularity in the timing and number of meals 298

consumed and a later timing of meals. 17 20

Consistent with these changes in obesity-related 299

eating behavior in rotating shift workers, our previous studies have shown that rotating shift 300

workers consumed more confectioneries and sugar-sweetened beverages compared with day 301

workers, 7 and that the rate of skipping breakfast on days on the day shift in rotating shift 302

workers was significantly higher compared with day workers among female nurses 8 in large 303

population studies. Furthermore, the preference for a high-fat diet was confirmed following a 304

simulated night shift. 25

305

306

Chronic positive energy balance is one of the well-known causes of lifestyle-related diseases 307

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which are mediated by obesity. The positive energy balance is caused by the excess dietary 308

intake relative to energy expenditure, and can be relatively easily induced by consuming large 309

portions of food 26

and/or high energy-dense food such as snacks and confectioneries. 27

In our 310

samples, the score for meal contents was significantly and positively associated with BMI 311

(Pearson's correlation = 0.186, p = 0.031). Recently, studies have shown that the timing of 312

meal intake (i .e., skipping breakfast, greater caloric intake at dinner, or later t iming of dinner) 313

also contributed to increases in BMI and the higher risk of obesity, 5 28

after statistically 314

controlling for total energy intake, in individuals who do not engage in night shift work. In 315

our samples, the score for temporal dietary patterns was significantly and positively associated 316

with BMI (Pearson's correlation = 0.281, p = 0.005). Regarding rotating shift workers, it has 317

been found that nocturnal energy intake (00:00–04:00) on days on the night shift was 318

associated with increases in body weight. 29

Another recent study found that the significant 319

effects of rotating shift work on BMI remained after controlling for daily total energy intake 320

and daily physical activity. 7 With regard to the physiological background of these relations, 321

the timing of meals might change the lipid metabolism. 4 30 31

Considered together with 322

higher scores for meal contents and temporal eating patterns in rotating shift workers (Table 2) 323

compared with those scores of day workers and normal-weight women, 32

the timing of meal 324

intake, as well as meal contents, may be an important factor in prevention and improvement of 325

obesity and lifestyle-related diseases in rotating shift workers, and this should be examined in 326

the future. In particular, studies on the effects of the timing of meal intake on days on the 327

night shift on BMI may be needed. 328

329

The means of BMI for day workers and rotating shift workers in our samples were not 330

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significantly different and fell in the normal range of BMI. However, it should be noted that 331

age was significantly higher in day workers, and that years of experience of rotating shift work 332

were significantly longer in day workers compared with rotating shift workers (Table 1). 333

Previous studies have indicated that duration of rotating shift work may have a positive 334

relationship with overweight/obesity 33

and increasing BMI, 7 indicating that there may be 335

accumulative effects of rotating shift work on BMI in day workers (Table.1). In addition, in 336

Japan, more than 20% of women in their 20s are underweight (BMI < 18.5 kg/m2).

34 This 337

percentage is much higher than in most developed countries. 35

Also, in epidemiological 338

studies using a larger sample size, mean BMI scores for rotating shift workers in Japanese 339

female nurses (e.g. Tada et al.; 21.6±3.2 kg/m2, n = 1579

7; Lee et al.; 22.3±3.0 kg/m

2, n = 340

18108 36

) were in the normal range, while this value in other countries was higher than the 341

normal range (e.g. Australian and New Zealand nurses; 26.4±5.3 kg/m2, n = 320

37; Canadian 342

nurses; 25.7±5.1 kg/m2, n = 4111

38). Considered together with the higher percentage of body 343

fat levels, especially at lower BMI, in Japanese compared with Caucasians and American 344

Blacks, 39

Japanese female nurses engaging in rotating shift work should be careful of gains in 345

BMI and/or the percentage of body fat as well as BMI. 346

347

There were several limitations to this study. First, the effect of other rotating shift systems on 348

eating behaviors remains unclear. Morikawa et al. 40

reported that people working on a 349

rotating 2-shift system had a higher risk of increased BMI compared with people working on a 350

rotating 3-shift system, indicating that the type of rotating shift system might affect eating 351

behavior. Second, the current participants were all Japanese female nurses at a particular city 352

hospital. Studies in other populations may be required to clarify to what extent the present 353

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results can be generalized. Finally, potential confounding variables such as psychological 354

stress and sensations of fatigue may not have been fully considered. 355

356

Conclusions 357

In conclusion, rotating shift work was associated with a more unbalanced diet and abnormal 358

temporal eating patterns, and the associations may be mediated and/or modulated partly by 359

being of the Evening type. These findings have important implications for the development 360

of novel strategies for preventing excessive weight gain in rotating shift workers. 361

362

Acknowledgments 363

We thank the chief nurses and staff of each medical ward in Ome City General Hospital, and all 364

persons who cooperated in conducting this study. 365

366

Contributorship statement 367

TY, YK, ON, JO, RT and FT designed the research; TY, AS, YY, AH, and YT conducted the 368

research; TY, YT, and FT analyzed the data; TY, YK, and FT wrote the manuscript; TY had 369

primary responsibility for the final content. All the authors read and approved the final 370

manuscript. 371

372

Competing interests 373

The authors have no competing interests. 374

375

Funding 376

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This study was supported by a grant from the Japan Society for the Promotion of Science 377

(Grant-in-Aid for start-up 26882040). 378

379

Data sharing statement 380

No additional data available. 381

382

383

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STROBE Statement—checklist of items that should be included in reports of observational studies

Item

No Recommendation

Title and

abstract

1 (a) Indicate the study’s design with a commonly used term in the title or the

abstract

Page 1

(b) Provide in the abstract an informative and balanced summary of what was

done and what was found

Page 2

Introduction

Background

/rationale

2 Explain the scientific background and rationale for the investigation being

reported

Page 4-6

Objectives 3 State specific objectives, including any prespecified hypotheses Page 5

Methods

Study

design

4 Present key elements of study design early in the paper Page 8

Setting 5 Describe the setting, locations, and relevant dates, including periods of

recruitment, exposure, follow-up, and data collection

Page 7

Participants 6 (a) Cohort study—Give the eligibility criteria, and the sources and methods of

selection of participants. Describe methods of follow-up

Case-control study—Give the eligibility criteria, and the sources and methods

of case ascertainment and control selection. Give the rationale for the choice of

cases and controls

Cross-sectional study—Give the eligibility criteria, and the sources and

methods of selection of participants

Page 7

(b) Cohort study—For matched studies, give matching criteria and number of

exposed and unexposed

Case-control study—For matched studies, give matching criteria and the

number of controls per case

-

Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and

effect modifiers. Give diagnostic criteria, if applicable

Page 8

Data

sources/

measuremen

t

8* For each variable of interest, give sources of data and details of methods of

assessment (measurement). Describe comparability of assessment methods if

there is more than one group

Page 8

Bias 9 Describe any efforts to address potential sources of bias Page 9

Study size 10 Explain how the study size was arrived at Page 7

Quantitative

variables

11 Explain how quantitative variables were handled in the analyses. If applicable,

describe which groupings were chosen and why

Page 9

Statistical

methods

12 (a) Describe all statistical methods, including those used to control for

confounding

Page 9

(b) Describe any methods used to examine subgroups and interactions -

(c) Explain how missing data were addressed Page 7

(d) Cohort study—If applicable, explain how loss to follow-up was addressed

Case-control study—If applicable, explain how matching of cases and controls

was addressed

Cross-sectional study—If applicable, describe analytical methods taking

account of sampling strategy

Page 9

(e) Describe any sensitivity analyses -

Continued on next page

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Results

Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers

potentially eligible, examined for eligibility, confirmed eligible, included in the

study, completing follow-up, and analysed

Table 1, Page 10

(b) Give reasons for non-participation at each stage -

(c) Consider use of a flow diagram -

Descriptive

data

14* (a) Give characteristics of study participants (eg demographic, clinical, social)

and information on exposures and potential confounders

Table 1, Page 10

(b) Indicate number of participants with missing data for each variable of

interest

Table 1, Page 10

(c) Cohort study—Summarise follow-up time (eg, average and total amount) -

Outcome

data

15* Cohort study—Report numbers of outcome events or summary measures over

time

-

Case-control study—Report numbers in each exposure category, or summary

measures of exposure

-

Cross-sectional study—Report numbers of outcome events or summary

measures

Table 1, Page 10

Table 2, Page 11

Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates

and their precision (eg, 95% confidence interval). Make clear which

confounders were adjusted for and why they were included

Table 3, Page 13

(b) Report category boundaries when continuous variables were categorized -

(c) If relevant, consider translating estimates of relative risk into absolute risk

for a meaningful time period

-

Other

analyses

17 Report other analyses done—eg analyses of subgroups and interactions, and

sensitivity analyses

-

Discussion

Key results 18 Summarise key results with reference to study objectives Page 15

Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or

imprecision. Discuss both direction and magnitude of any potential bias

Page 18

Interpretation 20 Give a cautious overall interpretation of results considering objectives,

limitations, multiplicity of analyses, results from similar studies, and other

relevant evidence

Page 18

Generalisability 21 Discuss the generalisability (external validity) of the study results Page 18

Other information

Funding 22 Give the source of funding and the role of the funders for the present study and,

if applicable, for the original study on which the present article is based

Page 19

*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups

in cohort and cross-sectional studies.

Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published

examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the

Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at http://www.annals.org/, and

Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.

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Association of eating behaviors with diurnal preference and rotating shift work in Japanese female nurses: a cross-

sectional study

Journal: BMJ Open

Manuscript ID bmjopen-2016-011987.R1

Article Type: Research

Date Submitted by the Author: 12-Jul-2016

Complete List of Authors: Yoshizaki, Takahiro; Toyo University, Faculty of Food and Nutritional Sciences Kawano, Yukari; Tokyo University of Agriculture, Department of Nutritional

Science, Faculty of Applied Bio-Science Noguchi, Osamu; Ome City General Hospital, Department of Gastroenterology Onishi, Junko; Ome City General Hospital, Department of Nursing Teramoto, Reiko; Ome City General Hospital, Department of Clinical Nutrition Sunami, Ayaka; Tokyo University of Agriculture, Graduate School of Agriculture Yokoyama, Yuri; Tokyo University of Agriculture, Graduate School of Agriculture Tada, Yuki; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science

Hida, Azumi; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science Togo, Fumiharu; The University of Tokyo, Graduate School of Education

<b>Primary Subject Heading</b>:

Nutrition and metabolism

Secondary Subject Heading: Epidemiology, Occupational and environmental medicine, Public health

Keywords: Dietary habits, Chronotype, Rotating shift worker, Diurnal preference


BMJ Open on A

ugust 28, 2020 by guest. Protected by copyright.

http://bmjopen.bm

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1

Association of eating behaviors with diurnal preference and 1

rotating shift work in Japanese female nurses: a 2

cross-sectional study 3

4

Takahiro Yoshizaki1, Yukari Kawano

2, Osamu Noguchi

3, Junko Onishi

4, Reiko Teramoto

5, 5

Ayaka Sunami6, Yuri Yokoyama

6, Yuki Tada

2, Azumi Hida

2, Fumiharu Togo

7 6

7

1Faculty of Food and Nutritional Sciences, Toyo University, Gunma, Japan 8

2Department of Nutritional Science, Faculty of Applied Bio-Science, Tokyo University of 9

Agriculture, Tokyo, Japan 10

3Department of Gastroenterology, Ome City General Hospital, Tokyo, Japan 11

4Department of Nursing, Ome City General Hospital, Tokyo, Japan 12

5Department of Clinical Nutrition, Ome City General Hospital, Tokyo, Japan 13

6Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan 14

7Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo, 15

Tokyo, Japan 16

17

Running head: Rotating Shift Work and Eating Behaviors 18

Address correspondence to: 19

Takahiro Yoshizaki, Ph.D. 20

Faculty of Food and Nutritional Sciences, Toyo University 21

1-1-1 Izumino, Oura-gun, Itakura-machi, Gunma 374-0193, Japan 22

Tel: +81-276-82-9012 Fax: +81-276-82-9000 E-mail: [email protected] 23

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ABSTRACT 24

Objectives 25

Our study examines differences in eating behavior between day workers and rotating shift 26

workers, and considers whether diurnal preference could explain the differences. 27

Methods 28

Japanese female nurses were studied (39 day workers and 123 rotating shift workers, aged 21–29

63) using self-administered questionnaires. The questionnaires assessed eating behaviors, 30

diurnal preference, and demographic characteristics. The questionnaire in the Guidelines for 31

the management of obesity disease issued by the Japan Society for the Study of Obesity was 32

used to obtain scores for the levels of obesity-related eating behaviors, including cognition of 33

constitution, motivation for eating, eating as a diversion, feeling of satiety, eating style, meal 34

contents and temporal eating patterns. The Japanese version of the Morningness-Eveningness 35

(ME) questionnaire was used to measure self-rated preference for the degree to which people 36

prefer to be active in the morning or the evening (morningness-eveningness). 37

Results 38

The scores for meal contents and temporal eating patterns in rotating shift workers were 39

significantly higher than those in day workers. The ME score of rotating shift workers was 40

significantly lower, indicating greater eveningness/less morningness among rotating shift 41

workers. Multivariate linear regression revealed that the ME score was significantly 42

negatively associated with temporal eating patterns and showed a negative association with the 43

score for meal contents at a trend level, while current work shift was not significantly 44

correlated with the scores. 45

Conclusions 46

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3

These results suggest that eating behaviors for rotating shift workers are associated with a 47

more unbalanced diet and abnormal temporal eating patterns and that the associations may be 48

explained by diurnal preference rather than by rotating shift work. 49

50

Keywords: Dietary habits; Chronotype; Rotating shift worker 51

52

STRENGTHS and LIMITATIONS of THIS STUDY 53

・There are few studies that have clarified whether the difference of diurnal preference explains 54


・The aim of the present study was to elucidate the differences in obesity-related eating 56

behavior between day workers and rotating shift workers, considering the diurnal preference, 57

among Japanese female nurses. 58

・Eating behaviors for rotating shift workers were associated with more unbalanced diets and 59

more abnormal temporal eating patterns, which may be explained by the diurnal preference 60

rather than by rotating shift work. 61

・These findings have important implications for the development of novel strategies for 62

preventing excessive weight gain in rotating shift workers. 63

・Variables, such as eating behaviors and diurnal preference, were self-reported. Continuous 64

monitoring of dietary intake and the sleep–wake cycle may be needed in future research. 65

66

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4

1. INTRODUCTION 67

The growth in the proportion of the population aged 65 years old and over leads to an increase 68

in the social demand for nurses in medical facilities. Among them, health problems can be 69

caused by severe working conditions such as shifting of work schedules between the day and 70

night (i.e., rotating shift work). Previous studies have suggested that rotating shift work is 71

related to higher r isks of health problems, including obesity, increases in body mass index 72

(BMI), and adiposity with abnormal metabolism, compared with fixed day work. 1-3

One of the 73

possible factors for increasing the risks of these health problems in rotating shift workers is 74

their altered eating behavior. 4 5

Our previous studies demonstrated that female workers who 75

engaged in rotating shift work consumed more sugar-sweetened beverages and snacks than day 76

workers, 6 7

and that the rate of subjects who reported skipping breakfast almost everyday (80–77

100%) on days on the day shift was significantly higher in rotating shift workers compared 78

with day workers. 8 Recent studies by other groups have also showed that rotating shift workers 79

had irregular meal times (e.g., skipping meals or midnight snacks), 9 and unbalanced dietary 80

intake (e.g., greater intake of fats and oils and lower intake of vegetables) when compared with 81

day workers. 10

However, it is unclear which aspects of obesity-related eating behavior change 82

in rotating shift workers, and which factors contribute to the altered eating behaviors in 83


85

One plausible mechanism contributing to the altered eating behaviors in rotating shift workers 86

is a disturbed circadian rhythm. Our previous study revealed that rotating shift workers had a 87

significant phase delay in the 24-h rhythm of cardiac autonomic nervous system activity 88

compared with fixed day workers, 11

suggesting a phase delay of the circadian rhythm among 89

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rotating shift workers. The endogenous circadian clocks, controlled by the master circadian 90

clock in the suprachiasmatic nuclei of the hypothalamus, play a significant role in regulating a 91

number of circadian and daily physiological rhythms, including feeding behavior. 12

For 92

example, a human laboratory study showed that the circadian clock regulated hunger and 93

appetite independently of the fasting-feeding rhythm and the sleep-wake cycle, 13

indicating 94

that the phase delay of the circadian clock might modify the timing of eating. Moreover, a 95

recent study revealed that a late midpoint of nocturnal sleep was associated with increases in 96

energy intake from undesirable dietary contents such as alcoholic beverages, confectioneries, 97

fats and oils, and meats in individuals who did not engage in night shift work. 14

Despite these 98

available data, which suggest a possibility of a close association between eating behavior and 99

the circadian clock, there are few studies that have clarified whether the association explains 100


102

To investigate epidemiologically the phase of the circadian clock during daily life, individual 103

preference in the phase of the sleep-wake cycle (i.e. , diurnal preference, 104

morningness-eveningness, or chronotype), which may be different from the actual sleep-wake 105

cycle during daily life, was assessed using the Japanese version of the 106

Morningness-Eveningness questionnaire by Torsvall and Akerstedt. 15 -18

Diurnal preference 107

(e.g., evening type or morning type) are attributed to differences in the phase of the circadian 108

clock. 19

Therefore, the aim of the present study was to elucidate the association between 109

rotating shift work and obesity-related eating behaviors, considering the diurnal preference, 110

among Japanese female nurses. Eating behaviors were investigated using the questionnaire in 111

the Guidelines for the management of obesity disease issued by the Japan Society for the Study 112

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of Obesity. 20 21

Characteristics of eating behavior which were different between overweight 113

and normal weight individuals were extracted from an interview survey and compiled to 114

produce the questionnaire. 22

Our hypothesis was that rotating shift workers would have 115

obesity-related eating behaviors associated with meal contents (e.g., greater intake of specific 116

nutrients) and temporal eating patterns (e.g., skipping breakfast and/or late dinner), and that 117

diurnal preference would partially explain the differences in obesity-related eating behaviors 118

between day workers and rotating shift workers. 119

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2. METHODS 120

2.1 Participants 121

The study population consisted of nurses working at a general hospital in the center of Ome 122

city. Ome city is located in the west side of the Tokyo metropolitan area and is the fifth 123

largest city in the metropolis. Urbanization and industrialization are present in the region of 124

the plain, while districts in the hilly area in the western region of the city have rural 125

populations. A total of 506 nurses were handed the questionnaires by the chief nursing officer 126

on each ward. The purpose of this study and data handling procedures were described in a 127

cover letter with the questionnaire. Agreement to participate in this study was assumed on the 128

basis of receipt of an anonymous questionnaire. A total of 218 nurses (43.1%; age 19–63 yr) 129

responded. Among them, 56 were excluded from the analysis because of missing data [age 130

(n=2), current work schedules (n=6), residential status (n=1), marital status (n=2), years of 131

experience as a rotating shift worker (n=23), smoking status (n=2), alcohol status (n=4), 132

number of night shifts during the previous month (n=6), and the questionnaire about diurnal 133

preference (n=13)]. Because the scoring method for the questionnaire about obesity-related 134

eating behavior was different for men and women, 23 24

we decided to exclude the small number 135

of data from male nurses (n=20). As a result, 162 female nurses (39 day workers and 123 136

shift workers) were analyzed (Figure 1). Their mean total duration of experience in their 137

current job was 12.2 ± 10.3 [SD] yr. In this study, individuals who worked fixed day shifts 138

only (i.e. 08:30–17:15 h) were defined as “day workers”, while those who worked in either a 139

two-shift system (days and nights, at 08:30–17:15 and 16:30–09:15 h) or a forward-rotating 140

three-shift system (days, evenings and nights, at 08:30–17:15, 16:30–01:00 and 00:45–09:15, 141

respectively) were classified as “rotating shift workers”. The mean number of night shifts 142

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was 7.6 ± 3.1 during the previous month. All the study procedures were reviewed and 143

approved by the Ethics Committee at the Tokyo University of Agriculture (No. 1111). 144

145

2.2 Assessments 146

A cross-sectional study using self-administered questionnaires on demographic characteristics, 147

diurnal preference and eating behavior was conducted in the general hospital at the beginning 148

of September 2012. Completed questionnaires were returned within two weeks. 149

Demographic characteristics of the participants included in the questionnaire were the 150

following: age, height, weight, current work schedule, years of experience in the current job 151

and as a rotating shift worker, marital status, residential status, smoking status, alcohol status, 152

and the number of night shifts during the previous month. Body mass index (BMI) was 153

calculated on the basis of self-reported height and weight [weight / height2 (kg / m

2)]. The 154

Japanese version of the Morningness-Eveningness questionnaire by Torsvall and Akerstedt was 155

used to measure self-rated preference for activity in the morning or the evening 156

(morningness-eveningness). 15 17 18

Based on seven items about daily sleep habits or preference 157

consisting of 0–3 Likert scales, the Morningness-Eveningness score (ME score) was calculated 158

(range: 7–28 points). A lower ME score indicates a tendency for a greater preference for 159

activity in the evening (evening type), while a higher ME score indicates a greater preference 160

for activity in the morning (morning type). We calculated the internal consistency for the 161

Morningness–Eveningness questionnaire using the present data, which revealed a Cronbach’s 162

alpha of 0.73. Data about habitual eating behaviors during the previous month were obtained 163

from the response to the eating behavior questionnaire issued by the Japan Society for the 164

Study of Obesity, 20 21

which was developed to detect obesity-related eating behavior. The 165

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details of the contents of the questionnaire have been shown in previous studies. 22 23 25 26

In 166

brief, each of the 55 items on eating habits is rated on a four-point scale ranging from “strongly 167

disagree” to “strongly agree”. These items form seven separate scales: cognition of 168

constitution (range: 6–24), motivation for eating (range: 9–36), eating as a diversion (range: 4–169

16), feeling of satiety (range: 6–24), eating style (range: 5–20), meal contents (range: 7–28), 170

and temporal eating patterns (range: 8–32). Higher scores indicate more improper eating 171

behavior in terms of a higher probability of obesity. 22 23

We also calculated the internal 172

consistency using the data in this study, with Cronbach’s alpha found to be 0.62 for cognition 173

of constitution, 0.82 for motivation for eating, 0.71 for eating as diversion, 0.63 for feeling of 174

satiety, 0.82 for eating style, 0.77 for meal contents and 0.71 for temporal eating patterns. 175

176

2.3 Statistical analysis 177

After the normal distr ibution of variables had been tested by Kolmogorov-Smirnov test, the 178

t-test or Mann–Whitney U test and the χ2 test or Fisher 's exact test were used for continuous 179

and categorical variables, respectively, to compare the difference in demographic 180

characteristics, the ME score, and the scores for eating behavior between day workers and 181

rotating shift workers. For categorical variables, residuals between the observed and 182

expected frequencies were standardized to determine cells which were statistically different 183

from expected values. Effect sizes for the difference in the scores of eating behavior between 184

the groups were assessed using Cohen’s d. Simple and multivariate linear regression (model 185

1) were performed with each score for eating behavior (meal contents or temporal eating 186

patterns) as dependent variables, and current work schedule (0 = day work, 1 = rotating shift 187

work) and the ME score (continuous, in points) as independent variables. The model was 188

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extended (model 2) using an interaction term (shift work × ME score) with the following 189

demographic characteristics for covariate adjustment: age (continuous, in years), years of 190

experience as a rotating shift worker (continuous, in years), marital status (0 = married, 1 = 191

unmarried or divorced), residential status (0 = living alone, 1 = not living alone), smoking 192

status (‘Do you smoke?’; 0 = no, 1 = yes), alcohol status (‘Do you drink alcohol?’; 0 = no, 1 = 193

yes) and the number of night shifts during the previous month (continuous, in days). All 194

statistical analyses were performed with an SPSS statistical software package (IBM SPSS 22.0 195

for Windows, SPSS Japan). P values less than 0.05 were considered statistically significant 196

using two-tailed tests. 197

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3. RESULTS 198

The demographic characteristics of day workers and rotating shift workers are shown in Table 199

1. Age was significantly higher in day workers compared with rotating shift workers (p < 200

0.05). The years of experience in the current work schedule were significantly more in day 201

workers compared with rotating shift workers (p < 0.05). Marital status and residential status 202

were significantly associated with the current work schedule (p < 0.05). The ME score for 203

rotating shift workers was significantly lower compared with day workers (p < 0.05), 204

indicating greater eveningness/less morningness among rotating shift workers compared with 205

day workers. This significant difference was not attenuated after controlling for age as a 206

confounding variable (data not shown). 207

208

Table 1 Demographic characteristics of day workers and rotating 209

shift workers 210

Day workers Shift workers

P values

n=39 n=123

Age† (years) 44.2 ± 10.9 34.7 ± 8.7 < 0.001

Height†a

(cm) 156.7 ± 5.6 157.5 ± 5.5 0.175

Weight†b

(kg) 53.4 ± 8.3 53.8 ± 8.9 0.784

BMI†c

(kg/m2) 21.7 ± 2.7 21.7 ± 3.5 0.676

ME score†§

(points) 20.8 ± 3.3 17.1 ± 4.0 < 0.001

Years of experience

Current work† (years) 17.4 ± 12.0 10.6 ± 9.2 0.002

Rotating shift work† (years) 11.8 ± 10.7 9.7 ± 8.7 0.652

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Number of night shifts (day/month) 0.0 ± 0.0 7.6 ± 3.1 -

Marital status‡ Married 32 ( 82 )

* 50 ( 41 )

0.001

Unmarried or divorced 7 ( 18 ) 73 ( 59 ) *

Residential status‡ Living alone 3 ( 8 ) 33 ( 27 )

*

0.014

Not living alone 36 ( 92 ) * 90 ( 73 )

Smoking status Yes 4 ( 10 ) 17 ( 14 )

0.785

No 35 ( 90 ) 106 ( 86 )

Alcohol status‡ Yes 21 ( 54 ) 51 ( 41 )

0.198

No 18 ( 46 ) 72 ( 59 )

211

Values are means ± standard deviation or number (%). 212

BMI, body mass index; ME score, Morningness-Eveningness score 213 †Mann-Whitney U test 214

‡χ

2 test or Fisher's exact test (When p < 0.05, standardized residuals were determined for each 215

cell.) 216 *p < 0.05 217

§A lower ME score is indicative of the evening type. 218


219


220

cShift workers, n=118

221

222

Scores for the obesity-related eating behaviors of day workers and rotating shift workers are 223

shown in Table 2. The scores for meal contents and temporal eating patterns significantly 224

differed between the groups (p < 0.05), indicating an unbalanced diet and more irregular timing 225

of meals among rotating shift workers compared with day workers. Scores for other eating 226

behaviors did not differ between the groups (p > 0.05). 227

228

229

Table 2 Scores for habitual eating behavior in day workers and 230

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rotating shift workers 231

Normal Day workers Shift workers

Cohen’s d p values

(Ref. 23) n=39 n=123

Cognition of constitution†a

(points) 14 14.3 ± 3.4 13.6 ± 3.7 –0.19 0.328

Motivation for eating‡b

(points) 18 19.5 ± 4.9 18.8 ± 5.6 –0.13 0.384

Eating as a diversion‡c

(points) 7 7.4 ± 2.4 7.1 ± 2.9 –0.11 0.310

Feeling of satiety‡ (points) 10 10.9 ± 3.1 11.3 ± 3.2 0.13 0.427

Eating style‡ (points) 9 9.8 ± 3.5 9.7 ± 3.6 –0.03 0.629

Meal contents‡ (points) 12 13.9 ± 3.9 15.6 ± 4.5 0.39 0.045

Temporal eating patterns‡d

(points) 16 16.5 ± 4.5 19.5 ± 4.8 0.63 0.001

232

Values are means ± standard deviation. 233

Higher scores indicate more improper eating behavior in terms of a higher probability of 234

obesity: Cognition of weight and constitution, having false recognition of and assumptions 235

about reasons for weight gain; Motivation for eating, having behavioral factors which can 236

induce over-eating; Eating as a diversion, being subject to psychological factors which increase 237

appetite (i.e., perceived mental stress); Feeling of satiety, being prone to have an appetite and 238

to eat as much as possible; Eating style, being prone to eat fast; Meal contents, having a 239

preference for a high fat diet and sweets (e.g., confectioneries and sweet buns); Temporal 240

eating patterns, irregularity of timing and number of meals taken during the day and delay in 241

timing of meals. 242 †t-test 243

‡Mann-Whitney U test 244


245


246

cDay workers, n=38

247

dShift workers, n=119

248

249

We examined the relationship between rotating shift work, the ME score, and scores for meal 250

contents and temporal eating patterns using simple and multivariate linear regression. Simple 251

linear regression (Table 3, Figure 2) showed that rotating shift work and a lower ME score were 252

significantly (p < 0.05) associated with higher scores for meal contents and temporal eating 253

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patterns. Multivariate linear regression (model 1) showed that the ME score was significantly 254

(p < 0.05) associated with the score for meal contents, while the effect of rotating shift work 255

was not (p = 0.245). Regarding temporal eating patterns, the ME score was significantly 256

associated with the score (p < 0.05), while rotating shift work was attenuated to a trend level 257

only (p = 0.060). In model 2, in which the variables of demographic characteristics which 258

significantly (p < 0.05) differed between the groups (i.e., age, years of experience as a rotating 259

shift worker, marital status, residential status, and number of night shifts during the previous 260

month) and smoking and alcohol status were controlled, the correlations with the ME score 261

decreased slightly but remained significantly negative (β = –0. 338, p < 0.05) for temporal 262

eating patterns or at a trend level (β = –0.196, p = 0.051) for meal contents, while there were 263

no significant interactions between shift work and the ME score with the scores for meal 264

contents and temporal eating patterns. 265

266

Table 3 Association of current shift schedule (rotating shift work) 267

and diurnal preference with scores for meal contents and temporal 268

eating patterns in multivariate linear regression models 269

Independent

variables

Unstandardized

coefficients

Standardized

coefficients p values

B SE β

Meal contents

Crude


ME score –0.223 0.082 –0.210 0.007

Model 1


ME score –0.183 0.089 –0.172 0.041

Model 2a


ME score –0.208 0.106 –0.196 0.051

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Shift work × ME score 0.222 0.247 0.100 0.371

Temporal eating patterns

Crude

Rotating shift work 3.211 0.867 0.284 < 0.001

ME score –0.465 0.086 –0.397 < 0.001

Model 1


ME score –0.395 0.093 –0.338 < 0.001

Model 2a


ME score –0.395 0.110 –0.338 < 0.001

Shift work × ME score –0.061 0.255 –0.025 0.811 270 aAdjusted by age, years of experience as a rotating shift worker, marital status, residential 271

status, smoking status, alcohol status, and number of night shifts during the previous month. 272

Years of experience in the current work schedule were not included in Model 2 because of a 273

high level of multicollinearity (Variance inflation factor = 8.101). 274

275

276

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4. DISCUSSION 277

Our cross-sectional study explored the differences in obesity-related eating behavior between 278

day workers and rotating shift workers, considering diurnal preference, among Japanese female 279

nurses. Scores for meal contents and temporal eating patterns were significantly higher in 280

rotating shift workers than in day workers (p < 0.05). The ME score of rotating shift workers 281

was significantly (p < 0.05) lower compared with day workers, indicating greater 282

eveningness/less morningness among rotating shift workers. Multivariate linear regression 283

revealed that the correlation with the ME score was significantly negative (β = –0.338, p < 284

0.05) for the score for temporal eating patterns and showed a negative association with the 285

score for meal contents at a trend level (β = –0.196, p = 0.051), while current work shift (i.e., 286

rotating shift work) was not significantly correlated with the scores. These results suggest 287

that eating behaviors for rotating shift workers are associated with a more unbalanced diet and 288

abnormal temporal eating patterns and that the associations could be explained by diurnal 289

preference (e.g., greater eveningness/less morningness) rather than by rotating shift work. To 290

the best of our knowledge, this is the first study to show the associations between rotating shift 291

work, diurnal preference, and eating behavior. 292

293

Given the fact that the evening type closely correlates with delays in the phase angle of the 294

circadian rhythm 19

and that the phase delay can be caused by light exposure and sleep/dark 295

schedules during nights on the days of the night shift, 27

our study indicates that being of 296

greater eveningness/less morningness, or the phase delay of the circadian rhythm, may 297

correlate with altered eating behavior in rotating shift workers. This indication is supported 298

by previous studies. 11 28

For example, one previous study revealed that rotating shift workers 299

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showed a phase delay in the circadian rhythm compared with day workers. 11

In addition, 300

rotating shift workers have a tendency for more evening types compared with day workers, 8 29

301

which is consistent with our results. We also demonstrated that a greater phase delay of the 302

circadian rhythm was associated with a later timing of breakfast among rotating shift workers. 303

28 However, causality between diurnal preference or phase angle of the circadian rhythm and 304

altered eating behavior could not be examined, although these may have interactive effects. I t 305

should be explored in future studies whether changes from the evening type to the morning 306

type in diurnal preference or the phase advance of the circadian rhythm would improve eating 307

behavior in rotating shift workers. 308

309

Our results show that rotating shift work is associated with higher scores for meal contents and 310

temporal eating patterns. A higher score for meal contents represents a greater preference for 311

a high-fat diet and sweets (e.g., confectioneries and sweet buns). 21 23 25

A higher score for 312

temporal eating patterns represents a greater irregularity in the timing and number of meals 313

consumed and a later timing of meals. 21 23

Consistent with these changes in obesity-related 314

eating behavior in rotating shift workers, our previous studies have shown that rotating shift 315

workers consumed more confectioneries and sugar-sweetened beverages compared with day 316

workers, 7 and that the rate of skipping breakfast on days on the day shift in rotating shift 317

workers was significantly higher compared with day workers among female nurses 8 in large 318

population studies. Furthermore, the preference for a high-fat diet was confirmed following a 319

simulated night shift. 30

320

321

Chronic positive energy balance is one of the well-known causes of lifestyle-related diseases 322

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which are mediated by obesity. The positive energy balance is caused by the excess dietary 323

intake relative to energy expenditure, and can be relatively easily induced by consuming large 324

portions of food 31

and/or high energy-dense food such as snacks and confectioneries. 32

In our 325

samples, the score for meal contents was significantly and positively associated with BMI 326

(Pearson's correlation = 0.186, p = 0.031). Recently, studies have shown that the timing of 327

meal intake (i .e., skipping breakfast, greater caloric intake at dinner, or later t iming of dinner) 328

also contributed to increases in BMI and the higher risk of obesity, 5 33

after statistically 329

controlling for total energy intake, in individuals who do not engage in night shift work. In 330

our samples, the score for temporal dietary patterns was significantly and positively associated 331

with BMI (Pearson's correlation = 0.281, p = 0.005). Regarding rotating shift workers, it has 332

been found that nocturnal energy intake (00:00–04:00) on days on the night shift was 333

associated with increases in body weight. 34

Another recent study found that the significant 334

effects of rotating shift work on BMI remained after controlling for daily total energy intake 335

and daily physical activity. 7 With regard to the physiological background of these relations, 336

the timing of meals might change the lipid metabolism. 4 35 36

Considered together with higher 337

scores for meal contents and temporal eating patterns in rotating shift workers (Table 2) 338

compared with those scores of day workers and normal-weight women, 23

the timing of meal 339

intake, as well as meal contents, may be an important factor in prevention and improvement of 340

obesity and lifestyle-related diseases in rotating shift workers, and this should be examined in 341

the future. In particular, studies on the effects of the timing of meal intake on days on the 342

night shift on BMI may be needed. 343

344

The means of BMI for day workers and rotating shift workers in our samples were not 345

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significantly different and fell in the normal range of BMI. However, it should be noted that 346

age was significantly higher in day workers, and that years of experience of rotating shift work 347

were significantly longer in day workers compared with rotating shift workers (Table 1). 348

Previous studies have indicated that duration of rotating shift work may have a positive 349

relationship with overweight/obesity 37

and increasing BMI, 7 indicating that there may be 350

accumulative effects of rotating shift work on BMI in day workers (Table.1). In addition, in 351

Japan, more than 20% of women in their 20s are underweight (BMI < 18.5 kg/m2).

38 This 352

percentage is much higher than in most developed countries. 39

Also, in epidemiological 353

studies using a larger sample size, mean BMI scores for rotating shift workers in Japanese 354

female nurses (e.g., Tada et al.; 21.6±3.2 kg/m2, n = 1579

7; Lee et al. ; 22.3±3.0 kg/m

2, n = 355

18108 40

) were in the normal range, while this value in other countries was higher than the 356

normal range (e.g., Australian and New Zealand nurses; 26.4±5.3 kg/m2, n = 320

41; Canadian 357

nurses; 25.7±5.1 kg/m2, n = 4111

42). Considered together with the higher percentage of body 358

fat levels, especially at lower BMI, in Japanese compared with Caucasians and American 359

Blacks, 43

Japanese female nurses engaging in rotating shift work should be careful of gains in 360

BMI and/or the percentage of body fat as well as BMI. 361

362

There were several limitations to this study. First, variables, such as eating behaviors and 363

diurnal preference, were self-reported. Continuous monitoring of dietary intake and the 364

sleep–wake cycle may be needed in future research. Second, the effect of other rotating shift 365

systems on eating behaviors remains unclear. Morikawa et al 44

reported that people working 366

on a rotating two-shift system had a higher risk of increased BMI compared with people 367

working on a rotating three-shift system, indicating that the type of rotating shift system might 368

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affect eating behavior. Third, the current participants were all Japanese female nurses at a 369

particular city hospital. Studies in other populations may be required to clarify to what extent 370

the present results can be generalized. Fourth, the unbalanced sample size between day and 371

shift workers may have contributed to a decrease in the statistical power to detect significant 372

differences in dietary behaviors between the groups, even though we could not detect 373

differences of a negligible effect size (absolute Cohen’s d < 0.15) or a lower range of a small 374

effect size (0.15 ≤ absolute Cohen’s d < 0.02) using statistical tests. Finally, potential 375

confounding variables, such as habitual sleep duration, daily variation in sleep timing, 376

psychological stress and sensations of fatigue, may not have been fully considered. 377

378

Conclusions 379

In conclusion, eating behaviors for rotating shift workers were associated with more 380

unbalanced diets and more abnormal temporal eating patterns, which may be explained by the 381

diurnal preference rather than by rotating shift work. These findings have important 382

implications for the development of novel strategies for preventing excessive weight gain in 383


385

Acknowledgments 386

We thank the chief nurses and staff of each medical ward in Ome City General Hospital, and all 387

persons who cooperated in conducting this study. 388

389

Contributorship statement 390

TY, YK, ON, JO, RT and FT designed the research; TY, AS, YY, AH, and YT conducted the 391

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research; TY, YT, and FT analyzed the data; TY, YK, and FT wrote the manuscript; TY had 392

primary responsibility for the final content. All the authors read and approved the final 393

manuscript. 394

395

Competing interests 396

The authors have no competing interests. 397

398

Funding 399

This study was supported by a grant from the Japan Society for the Promotion of Science 400

(Grant-in-Aid for start-up 26882040). 401

402

Data sharing statement 403

No additional data available. 404

405

406

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516

517

518

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Figure legends 519

Figure 1 Flowchart of study participants. 520

521

Figure 2 The relationship between the Morningness-Eveningness score 522

and the meal contents and temporal eating patterns scores. 523

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Figure 1 Flowchart of study participants.

190x142mm (300 x 300 DPI)

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Figure 2 The relationship between the Morningness-Eveningness score and the meal contents and temporal

eating patterns scores.

201x140mm (300 x 300 DPI)

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STROBE Statement—checklist of items that should be included in reports of observational studies

Item

No Recommendation

Title and

abstract

1 (a) Indicate the study’s design with a commonly used term in the title or the

abstract

Page 1

(b) Provide in the abstract an informative and balanced summary of what was

done and what was found

Page 2

Introduction

Background

/rationale

2 Explain the scientific background and rationale for the investigation being

reported

Page 4-6

Objectives 3 State specific objectives, including any prespecified hypotheses Page 5

Methods

Study

design

4 Present key elements of study design early in the paper Page 8

Setting 5 Describe the setting, locations, and relevant dates, including periods of

recruitment, exposure, follow-up, and data collection

Page 7

Participants 6 (a) Cohort study—Give the eligibility criteria, and the sources and methods of

selection of participants. Describe methods of follow-up

Case-control study—Give the eligibility criteria, and the sources and methods

of case ascertainment and control selection. Give the rationale for the choice of

cases and controls

Cross-sectional study—Give the eligibility criteria, and the sources and

methods of selection of participants

Page 7

(b) Cohort study—For matched studies, give matching criteria and number of

exposed and unexposed

Case-control study—For matched studies, give matching criteria and the

number of controls per case

-

Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and

effect modifiers. Give diagnostic criteria, if applicable

Page 8

Data

sources/

measuremen

t

8* For each variable of interest, give sources of data and details of methods of

assessment (measurement). Describe comparability of assessment methods if

there is more than one group

Page 8

Bias 9 Describe any efforts to address potential sources of bias Page 9

Study size 10 Explain how the study size was arrived at Page 7

Quantitative

variables

11 Explain how quantitative variables were handled in the analyses. If applicable,

describe which groupings were chosen and why

Page 9

Statistical

methods

12 (a) Describe all statistical methods, including those used to control for

confounding

Page 9

(b) Describe any methods used to examine subgroups and interactions -

(c) Explain how missing data were addressed Page 7

(d) Cohort study—If applicable, explain how loss to follow-up was addressed

Case-control study—If applicable, explain how matching of cases and controls

was addressed

Cross-sectional study—If applicable, describe analytical methods taking

account of sampling strategy

Page 9

(e) Describe any sensitivity analyses -

Continued on next page

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Results

Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers

potentially eligible, examined for eligibility, confirmed eligible, included in the

study, completing follow-up, and analysed

Table 1, Page 10

(b) Give reasons for non-participation at each stage -

(c) Consider use of a flow diagram -

Descriptive

data

14* (a) Give characteristics of study participants (eg demographic, clinical, social)

and information on exposures and potential confounders

Table 1, Page 10

(b) Indicate number of participants with missing data for each variable of

interest

Table 1, Page 10

(c) Cohort study—Summarise follow-up time (eg, average and total amount) -

Outcome

data

15* Cohort study—Report numbers of outcome events or summary measures over

time

-

Case-control study—Report numbers in each exposure category, or summary

measures of exposure

-

Cross-sectional study—Report numbers of outcome events or summary

measures

Table 1, Page 10

Table 2, Page 11

Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates

and their precision (eg, 95% confidence interval). Make clear which

confounders were adjusted for and why they were included

Table 3, Page 13

(b) Report category boundaries when continuous variables were categorized -

(c) If relevant, consider translating estimates of relative risk into absolute risk

for a meaningful time period

-

Other

analyses

17 Report other analyses done—eg analyses of subgroups and interactions, and

sensitivity analyses

-

Discussion

Key results 18 Summarise key results with reference to study objectives Page 15

Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or

imprecision. Discuss both direction and magnitude of any potential bias

Page 18

Interpretation 20 Give a cautious overall interpretation of results considering objectives,

limitations, multiplicity of analyses, results from similar studies, and other

relevant evidence

Page 18

Generalisability 21 Discuss the generalisability (external validity) of the study results Page 18

Other information

Funding 22 Give the source of funding and the role of the funders for the present study and,

if applicable, for the original study on which the present article is based

Page 19

*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups

in cohort and cross-sectional studies.

Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published

examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the

Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at http://www.annals.org/, and

Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.

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