mediterranean diet and breast cancer

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Conformity to traditional Mediterranean diet and breast cancer risk in the Greek EPIC (European Prospective Investigation into Cancer and Nutrition) cohort 1–3 Antonia Trichopoulou, Christina Bamia, Pagona Lagiou, and Dimitrios Trichopoulos ABSTRACT Background: Studies in the United States report inverse associa- tions of the Mediterranean dietary pattern with breast cancer risk, and several studies in Mediterranean countries indicate inverse as- sociations of breast cancer risk with intake of olive oil, a constitu- tional component of this diet. No study, however, has evaluated the association of the traditional Mediterranean diet with breast cancer in a Mediterranean country. Objective: We studied the relation of conformity to the Mediterranean diet with breast cancer risk in the context of the European Prospec- tive Investigation into Cancer and Nutrition cohort in Greece. Design: We followed up 14,807 women for an average of 9.8 y and identified 240 incident breast cancer cases. Diet was assessed through a validated food-frequency questionnaire, and conformity to the Mediterranean diet was evaluated through a score (range = 0–9 points) incorporating the characteristics of this diet. Results: Increasing conformity to the Mediterranean diet was not as- sociated with lower breast cancer risk in the entire cohort [hazard ratio (HR) = 0.88 for every 2 points; 95% CI: 0.75, 1.03] or in premenopausal women (HR = 1.01 for every 2 points; 95% CI: 0.80, 1.28), but there was a marginally significant inverse associa- tion among postmenopausal women (HR = 0.78 for every 2 points; 95% CI: 0.62, 0.98; P for interaction by menopausal status = 0.05). Conclusions: Conformity to the traditional Mediterranean diet may be associated with lower breast cancer risk among postmenopausal women and could explain, in part, the lower incidence of this dis- ease in Mediterranean countries. Am J Clin Nutr 2010;92:620– 5. INTRODUCTION The concept of the traditional Mediterranean diet was in- troduced by Ancel Keys in the early 1960s, with emphasis on the diet’s low content of saturated lipids and ecologic association with low incidence of coronary artery disease (1). In the 1980s, interest in the Mediterranean diet as an integral entity was renewed (2) and in 1995 a simple score assessing conformity to the salient char- acteristics of the Mediterranean diet was introduced (3). This score, or variants of it (4–7), have allowed the evaluation in cohort studies of the relation between conformity to this diet and several out- comes, including total mortality (8), incidence of or mortality from cardiovascular diseases (9), as well as incidence of or mortality from cancer overall (7, 10) or from specific cancer sites (11–13). With respect to breast cancer, a major cohort study in the United States has evaluated associations of several diet quality scores with postmenopausal breast cancer risk by estrogen receptor (ER) status (11). The authors reported no association of any of these scores with ER-positive breast cancer risk, but inverse associations of all the evaluated diet quality scores, including an alternate Mediter- ranean Diet Score (MDS), with ER-negative breast cancer incidence. We studied the relation of conformity to the Mediter- ranean diet with breast cancer risk in the context of the European Prospective Investigation into Cancer and nutrition (EPIC) cohort in Greece, a country in which large segments of the population still adhere to the traditional Mediterranean diet. SUBJECTS AND METHODS Study population The study population consisted of the women participating in the Greek segment of the European Prospective Investigation into Cancer and Nutrition (EPIC). EPIC is a prospective cohort study investigating the role of biological, dietary, lifestyle, and envi- ronmental factors in the etiology of cancer and other chronic diseases. It is conducted in 23 research centers in 10 European countries (14, 15). For Greece, the study protocol was approved by the ethics committees of the International Agency for Re- search on Cancer and the University of Athens Medical School. All participants provided written informed consent and all pro- cedures were in accordance with the Helsinki Declaration of 1975 as revised in 1983. In EPIC-Greece, between 1994 and 1999, 28,572 apparently healthy subjects (11,954 men and 16,618 women) aged 20–86 y were recruited from all over the country. Dietary and lifestyle questionnaires were administered to participants at enrollment 1 From the WHO Collaborating Center for Food and Nutrition Policies, Department of Hygiene, Epidemiology and Medical Statistics, Athens, Greece (AT, CB, and PL); the Hellenic Health Foundation, Athens, Greece (AT and DT); the Department of Epidemiology, Harvard School of Public Health, Boston, MA (PL and DT); and the Bureau of Epidemiologic Re- search, Academy of Athens, Athens, Greece (DT). 2 Supported by the Hellenic Ministry of Health, the Stavros Niarchos Foundation, and the Hellenic Health Foundation. 3 Address reprints requests and correspondence to D Trichopoulos, De- partment of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115. E-mail: [email protected]. Received April 1, 2010. Accepted for publication June 29, 2010. First published online July 21, 2010; doi: 10.3945/ajcn.2010.29619. 620 Am J Clin Nutr 2010;92:620–5. Printed in USA. Ó 2010 American Society for Nutrition at Brown Univ Sciences Lib/Med on March 22, 2011 www.ajcn.org Downloaded from

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The relationship between mediterranean diet and breast cancer

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Page 1: Mediterranean diet and breast cancer

Conformity to traditional Mediterranean diet and breast cancer risk inthe Greek EPIC (European Prospective Investigation into Cancer andNutrition) cohort1–3

Antonia Trichopoulou, Christina Bamia, Pagona Lagiou, and Dimitrios Trichopoulos

ABSTRACTBackground: Studies in the United States report inverse associa-tions of the Mediterranean dietary pattern with breast cancer risk,and several studies in Mediterranean countries indicate inverse as-sociations of breast cancer risk with intake of olive oil, a constitu-tional component of this diet. No study, however, has evaluated theassociation of the traditional Mediterranean diet with breast cancerin a Mediterranean country.Objective:We studied the relation of conformity to the Mediterraneandiet with breast cancer risk in the context of the European Prospec-tive Investigation into Cancer and Nutrition cohort in Greece.Design: We followed up 14,807 women for an average of 9.8 y andidentified 240 incident breast cancer cases. Diet was assessedthrough a validated food-frequency questionnaire, and conformityto the Mediterranean diet was evaluated through a score (range = 0–9points) incorporating the characteristics of this diet.Results: Increasing conformity to the Mediterranean diet was not as-sociated with lower breast cancer risk in the entire cohort [hazardratio (HR) = 0.88 for every 2 points; 95% CI: 0.75, 1.03] or inpremenopausal women (HR = 1.01 for every 2 points; 95% CI:0.80, 1.28), but there was a marginally significant inverse associa-tion among postmenopausal women (HR = 0.78 for every 2 points;95% CI: 0.62, 0.98; P for interaction by menopausal status = 0.05).Conclusions: Conformity to the traditional Mediterranean diet maybe associated with lower breast cancer risk among postmenopausalwomen and could explain, in part, the lower incidence of this dis-ease in Mediterranean countries. Am J Clin Nutr 2010;92:620–5.

INTRODUCTION

The concept of the traditional Mediterranean diet was in-troduced by Ancel Keys in the early 1960s, with emphasis on thediet’s low content of saturated lipids and ecologic association withlow incidence of coronary artery disease (1). In the 1980s, interestin the Mediterranean diet as an integral entity was renewed (2) andin 1995 a simple score assessing conformity to the salient char-acteristics of theMediterranean diet was introduced (3). This score,or variants of it (4–7), have allowed the evaluation in cohort studiesof the relation between conformity to this diet and several out-comes, including total mortality (8), incidence of or mortality fromcardiovascular diseases (9), as well as incidence of or mortalityfrom cancer overall (7, 10) or from specific cancer sites (11–13).With respect to breast cancer, a major cohort study in the UnitedStates has evaluated associations of several diet quality scores withpostmenopausal breast cancer risk by estrogen receptor (ER) status

(11). The authors reported no association of any of these scoreswith ER-positive breast cancer risk, but inverse associations of allthe evaluated diet quality scores, including an alternate Mediter-ranean Diet Score (MDS), with ER-negative breast cancerincidence. We studied the relation of conformity to the Mediter-ranean diet with breast cancer risk in the context of the EuropeanProspective Investigation into Cancer and nutrition (EPIC) cohortin Greece, a country in which large segments of the population stilladhere to the traditional Mediterranean diet.

SUBJECTS AND METHODS

Study population

The study population consisted of the women participating inthe Greek segment of the European Prospective Investigation intoCancer and Nutrition (EPIC). EPIC is a prospective cohort studyinvestigating the role of biological, dietary, lifestyle, and envi-ronmental factors in the etiology of cancer and other chronicdiseases. It is conducted in 23 research centers in 10 Europeancountries (14, 15). For Greece, the study protocol was approvedby the ethics committees of the International Agency for Re-search on Cancer and the University of Athens Medical School.All participants provided written informed consent and all pro-cedures were in accordancewith the Helsinki Declaration of 1975as revised in 1983.

In EPIC-Greece, between 1994 and 1999, 28,572 apparentlyhealthy subjects (11,954 men and 16,618 women) aged 20–86 ywere recruited from all over the country. Dietary and lifestylequestionnaires were administered to participants at enrollment

1 From the WHO Collaborating Center for Food and Nutrition Policies,

Department of Hygiene, Epidemiology and Medical Statistics, Athens,

Greece (AT, CB, and PL); the Hellenic Health Foundation, Athens, Greece

(AT and DT); the Department of Epidemiology, Harvard School of Public

Health, Boston, MA (PL and DT); and the Bureau of Epidemiologic Re-

search, Academy of Athens, Athens, Greece (DT).2 Supported by the Hellenic Ministry of Health, the Stavros Niarchos

Foundation, and the Hellenic Health Foundation.3 Address reprints requests and correspondence to D Trichopoulos, De-

partment of Epidemiology, Harvard School of Public Health, 677 Huntington

Avenue, Boston, MA 02115. E-mail: [email protected].

Received April 1, 2010. Accepted for publication June 29, 2010.

First published online July 21, 2010; doi: 10.3945/ajcn.2010.29619.

620 Am J Clin Nutr 2010;92:620–5. Printed in USA. � 2010 American Society for Nutrition

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by trained interviewers and somatometric measurements wereundertaken.

Data on diet

Usual dietary intakes during the year preceding enrollmentwere assessed by using a validated, semiquantitative, interviewer-administered, food-frequency questionnaire which included 150foods and beverages, as well as recipes commonly consumed inGreece (16). Standard portion sizes were used to estimate theconsumed quantities in grams per day. Nutrient and ethanolintakes (g/d), as well as total energy intakes (kcal/d) were cal-culated through the EPIC Nutrient Database (17). For thisanalysis, 11 food groups and nutrients were considered: vege-tables, legumes, fruit and nuts, dairy products, cereals, meat andmeat products, fish and seafood, olive oil, monounsaturatedlipids, saturated lipids, and ethanol.

Mediterranean diet scale

Conformity to the traditional Mediterranean diet was assessedthrough a score (range = 0–9 points) (4). The score relied on 9dietary components that are typical of the traditional Mediter-ranean diet. A value of 0 or 1 was assigned to each component ofthe score as follows: for components frequently consumed in thetraditional Mediterranean diet (vegetables, legumes, fruit andnuts, cereals, fish and seafood, as well a high ratio of mono-unsaturated to saturated lipids), women whose consumption wasbelow the median were assigned a value of 0, and 1 otherwise; forcomponents less frequently consumed in the traditional Medi-terranean diet (dairy, as well as meat and meat products), womenwhose consumption was below the median were assigned a valueof 1, and 0 otherwise. A value of 1 was also given to womenconsuming a moderate amount of ethanol (ie, between 5 and 25 g/d)and a value of 0 otherwise. Thus, the total MDS could takevalues from 0 (minimal adherence to the traditional Mediterra-nean diet) to 9 (maximal adherence to the traditional Mediter-ranean diet).

Lifestyle, anthropometric, dietary, and medical historydata

Sociodemographic and lifestyle characteristics (includingeducational achievement, smoking, and physical activity) wererecorded at enrollment. Physical activity was expressed as theusual daily energy expenditure in metabolic equivalent task(MET) hours per day (18). With respect to smoking, women werecategorized as never, current, and former smokers as of the date ofenrollment. Anthropometric measurements were obtained byusing standardized procedures (19). Body mass index (BMI) wasexpressed in kg/m2. Participants were also asked at enrollmentwhether they had ever had a medically documented diagnosis ofcertain diseases, including cancer.

Reproductive history data

Information on reproductive history was assessed througha section of the lifestyle questionnaire which was directed tofemales only. Specifically, women were asked about their age atmenarche, as well as their menopausal status at the time ofenrollment. Women who declared to have been post menopausal

were asked for their age at last menstrual cycle. All women wereasked about their parity status, age at first full term delivery andnumber of full term births (for parous women). Information oncurrent (at enrollment) or previous use of hormone replacementtherapy was also obtained.

Study participants and follow-up

In Greece, active follow-up by health professionals wasimplemented by means of telephone interviews of the participantor next of kin in case of a participant’s death. Self-reportedinformation on incident cancer was subsequently verified throughpathology reports, medical records, discharge diagnoses, or deathcertificates. The International Classification of Diseases forOncology (20) was used to classify cancers. For this study, in-cident breast cancer cases were defined as those with a verifiedpostrecruitment breast cancer diagnosis (International Classifi-cation of Diseases for Oncology code C50). If multiple incidentcancers were diagnosed in the same woman, we included thebreast cancer case only if it was the first malignancy diagnosedduring follow-up.

From the initial cohort of 16,618 female participants, weexcluded 446 (2.7%) women with cancer at enrollment. From theremaining 16,172 women, 520 were excluded because they werenot traced or did not respond during follow-up. Finally, for 845additional women, information was missing for one or more ofthe sociodemographic, dietary, somatometric, lifestyle, or re-productive history variables used in the present investigation.Thus, the final sample used for this analysis consisted of 14,807women without cancer at enrollment for whom vital status atfollow-up had been ascertained and for whom all the requiredinformation was available. As of December 2009, the meanfollow-up for the 14,807 women included in this study was 9.8 y,with a range of 23 d (a woman who died soon after enrollment) to15.8 y.

Statistical analysis

All analyses were performed with the STATA statisticalsoftware (version 11.0 for Windows; StataCorp, College Station,TX). Statistical significance was set at 2-sided P , 0.05. Simpletabulations were made for sociodemographic data, and meansand SDs were calculated for the dietary variables.Cox pro-portional hazards regression models were used to analyze sur-vival data with incident breast cancer being the event of interest.In these models, the time variable was the interval between thedate at enrollment and the date at diagnosis of breast cancer (forbreast cancer cases), or date of death for women who diedwithout having developed breast cancer (censored), or date oflast follow-up for women who were alive as of the date of lastcontact (censored).

With the Cox regression models we estimated the association ofMDS (in categories 0–3, 4–5, and 6–9, as well as per 2-pointincrement) with the incidence of breast cancer. We also evaluatedthe associations of each of the components of MDS (per incrementof intake set to a round number close to the SD of the relevantdaily intake) with the incidence of breast cancer. Analyses wereperformed for the overall female study population, as well asseparately for pre-/perimenopausal and postmenopausal women.Analyses were repeated after excluding follow-up of �1 y.

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TABLE 1

Mediterranean diet score, baseline characteristics, and breast cancer incidence among 14,807 participating women in the Greek European Prospective

Investigation into Cancer and Nutrition (EPIC) cohort study1

Mediterranean Diet Score

Age-adjusted hazard

ratios for death

(95% CI)2

Multivariate hazard

ratios for death

(95% CI)3

0–3 (n = 5098) 4–5 (n = 6386) 6–9 (n = 3323)

No. (%)

No. of

cases

Person-

years No. (%)

No. of

cases

Person-

years No. (%)

No. of

cases

Person-

years

Age at enrollment

,45 y 1550 (30.4) 22 14762 1922 (30.1) 22 18,305 991 (29.8) 13 9670 1.00 1.00

45 to ,55 y 1031 (20.2) 20 10417 1553 (24.3) 29 15,832 902 (27.1) 23 9262 1.51 (1.07, 2.14) 2.00 (1.38, 2.92)

55 to ,65 y 1185 (23.2) 27 11773 1609 (25.2) 29 16,181 881 (26.5) 10 9315 1.32 (0.93, 1.89) 2.95 (1.61, 5.40)

�65 y 1332 (26.1) 14 12115 1302 (20.4) 23 12,469 549 (16.5) 8 5374 1.13 (0.77, 1.68) 2.76 (1.43, 5.32)

Smoking status

Never 3778 (74.1) 62 36399 4647 (72.8) 74 45,972 2372 (71.4) 37 24,294 1.00 1.00

Former 963 (18.9) 14 9258 1259 (19.7) 18 12,170 649 (19.5) 14 6307 1.11 (0.78, 1.58) 0.98 (0.68, 1.41)

Current 357 (7.0) 7 3409 480 (7.5) 11 4645 302 (9.1) 3 3020 1.23 (0.77, 1.95) 1.01 (0.63, 1.63)

Highest educational

level achieved

None/elementary 3346 (65.6) 48 31,973 4006 (62.7) 63 39,449 1898 (57.1) 25 19,280 1.00 1.00

Secondary 1024 (20.1) 19 10,059 1435 (22.5) 22 14,133 816 (24.6) 16 8103 1.35 (0.97, 1.90) 1.26 (0.88, 1.81)

University degree

or higher

728 (14.3) 16 7035 945 (14.8) 18 9205 609 (18.3) 13 6237 1.64 (1.13, 2.38) 1.49 (0.99, 2.24)

BMI

�25 kg/m2 1254 (24.6) 19 12,196 1525 (23.9) 18 14,910 815 (24.5) 16 8074 1.00 1.00

.25 to ,30 kg/m2 1774 (34.8) 26 17,091 2383 (37.3) 43 23,578 1311 (39.5) 23 13,380 1.08 (0.76, 1.53) 1.19 (0.84, 1.70)

�30 kg/m2 2070 (40.6) 38 19,780 2478 (38.8) 42 24,299 1197 (36.0) 15 12,167 1.05 (0.74, 1.50) 1.24 (0.86, 1.81)

Physical activity4

,35.11 MET-h/d 2903 (56.9) 40 27,327 3097 (48.5) 54 30,157 1409 (42.4) 25 14,013 1.00 1.00

�35.11 MET-h/d 2195 (43.1) 43 21,739 3289 (51.5) 49 32,631 1914 (57.6) 29 19,608 0.96 (0.74, 1.24) 1.00 (0.77, 1.30)

Age at menarche

�11 y 550 (10.8) 13 5345 688 (10.8) 12 6746 379 (11.4) 7 3929 1.00 1.00

12 y 1228 (24.1) 17 11,912 1547 (24.2) 26 15,268 815 (24.5) 17 8074 0.85 (0.55, 1.30) 0.89 (0.58, 1.38)

13 y 1351 (26.5) 26 12,822 1683 (26.4) 27 16,465 904 (27.2) 16 9098 0.88 (0.58, 1.35) 0.95 (0.62, 1.46)

�14 y 1969 (38.6) 27 18,988 2468 (38.7) 38 24,309 1225 (36.9) 14 12,519 0.68 (0.45, 1.04) 0.75 (0.49, 1.15)

Menopausal status

Pre-/perimenopausal 2172 (42.6) 35 21,058 2841 (44.5) 44 27,741 1521 (45.8) 34 15,017 1.00 1.00

Postmenopauasal 2926 (57.4) 48 28,008 3545 (55.5) 59 35,046 1802 (54.2) 20 18,604 0.50 (0.30, 0.81) 0.51 (0.32, 0.84)

Age at menopause among

postmenopausal

women

,45 y 731 (25.0) 11 6898 845 (23.8) 13 8277 451 (25.0) 5 4623 1.005 1.005

45 to ,50 y 899 (30.7) 13 8738 1138 (32.1) 19 11,326 553 (30.7) 5 5712 0.96 (0.58, 1.56)5 0.97 (0.59, 1.58)5

�50 y 1296 (44.3) 24 12,373 1562 (44.1) 27 15,443 798 (44.3) 10 8268 1.15 (0.73, 1.80)5 1.15 (0.73, 1.81)5

No. of full term births

0 539 (10.6) 11 4982 635 (9.9) 10 6212 395 (11.9) 9 3836 1.00 1.00

1 530 (10.4) 10 5078 687 (10.8) 12 6641 375 (11.3) 10 3721 1.02 (0.62, 1.67) 1.04 (0.63, 1.72)

2 2539 (49.8) 39 24,737 3122 (48.9) 55 31,215 1597 (48.1) 25 16,341 0.79 (0.53, 1.18) 0.83 (0.55, 1.26)

.3 1490 (29.2) 23 14,271 1942 (30.4) 26 18,719 956 (28.8) 10 9722 0.66 (0.42, 1.03) 0.72 (0.45, 1.15)

Age at first delivery among

parous women

,25 y 2750 (60.3) 42 26,447 3374 (58.7) 45 32,914 1591 (54.3) 12 16,016 1.006 1.006

�25 to ,30 y 1242 (27.2) 19 11,992 1628 (28.3) 33 16,211 909 (31.1) 21 9324 1.48 (1.09, 2.00)6 1.38 (1.00, 1.90)6

�30 to ,35 y 422 (9.3) 9 4225 587 (10.2) 12 5794 325 (11.1) 9 3326 1.70 (1.13, 2.56)6 1.52 (0.98, 2.37)6

�35 y 145 (3.2) 2 1421 162 (2.8) 3 1657 103 (3.5) 3 1120 1.42 (0.69, 2.91)6 1.21 (0.57, 2.56)6

Hormone replacement therapy

among post- and

perimenopausal women

No 3032 (94.0) 53 29,126 3723 (93.4) 65 36,870 1888 (91.7) 27 19,342 1.007 1.007

Yes 195 (6.0) 4 1872 262 (6.6) 6 2677 172 (8.4) 4 1866 1.24 (0.71, 2.17)7 1.13 (0.64, 2.00)7

1 MET-h, metabolic equivalent task hours.2 Adjusted for age by using Cox regression.3 Mutually adjusted for the indicated factors by using Cox regression.4 Overall median MET-h/d = 35.11.5–7 Models were fitted among the following: 5postmenopausal women, 6parous women, 7post- and perimenopausal women.

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In all analyses, we controlled for age at enrollment (cate-gorically as ,45, 45–54, or �55 y), educational level (cate-gorically as none/elementary school degree, secondary school ortechnical school degree, or university degree or higher), smok-ing status at enrollment (categorically as never, former, or cur-rent), daily energy expenditure in MET hours per day (orderedas quintiles), total energy intake (ordered as quintiles), BMI(ordered as quintiles), height (ordered as quintiles), age atmenarche (ordered as �11, 12, 13, or �14 y), and ever use ofhormone replacement therapy (yes or no). The possible con-founding effects of parity and age at first delivery were alsoconsidered by including 2 variables in the models: one cate-gorical denoting whether parous at enrollment (yes = 1 or no = 0)and one continuous denoting the product of the parity categor-ical variable with the age at first delivery centered around themean age at first delivery (21). In analyses of the overall studypopulation, additional variables on menopausal status and ageat menopause were also included, again by using the same ap-proach (21). To accommodate the distinct association of BMIwith breast cancer incidence among pre-/perimenopausal andpostmenopausal women, an interaction term of menopausalstatus with BMI was also included in these models.

RESULTS

The characteristics for the 14,807 women in the cohort and the240 incident breast cancer cases, as recorded at recruitment byMDS, are shown in Table 1. As expected, among womenoverall, the incidence of breast cancer appears to increase with

age, educational level, BMI, age at menopause, age at first de-livery, and use of hormone replacement therapy; and to decreasewith age at menarche, parity and, controlling for age, followingmenopause. There were differences in the distributions of riskfactors by MDS, but these differences were all accounted for inthe multivariate analyses focusing on the association of con-formity to the Mediterranean diet and breast cancer risk.

The means and SDs of daily dietary intakes, as well as theassociated hazard ratios for incident breast cancer by incrementsin daily intake approximately equal to the corresponding SD arepresented in Table 2. Neither in the total cohort of women noramong premenopausal or postmenopausal women was therea statistically significant association, except with respect to fish(and seafood) intake, which appeared to be positively associ-ated with breast cancer risk among premenopausal women(P = 0.012) probably due to chance on account of multiplecomparisons.

Hazard ratios for incident breast cancer in relation to MDS,overall menopausal status, and by menopausal status are pre-sented in Table 3. Overall, increasing conformity to the Medi-terranean diet was not statistically significantly associated withrisk of breast cancer. Among postmenopausal women, however,there was a statistically significant inverse association of in-creased conformity to the Mediterranean diet with breast cancerrisk (HR per 2-point increment 0.78, 95% CI: 0.62, 0.98; P forinteraction by menopausal status = 0.05). We repeated theanalyses by substituting olive oil (greater than or equal to me-dian intake = 1 compared with less than median intake = 0) forthe ratio of monounsaturated to saturated lipids, and the results

TABLE 2

Means and SDs of daily dietary intakes among 14,807 women, and the associated hazard ratios (HRs; 95% CIs) for incident breast cancer (240 cases) per

indicated increments in daily intakes in the Greek European Prospective Investigation into Cancer and Nutrition (EPIC) cohort study1

Cohort Premenopausal Postmenopausal

Dietary variables Mean 6 SD Increment2 HR (95% CI)3 HR (95% CI)4 HR (95% CI)5 P6

Vegetables (g/d) 528.7 6 227.8 227 0.95 (0.82, 1.11) 0.95 (0.78, 1.15) 0.91 (0.70, 1.18) 0.365

Legumes (g/d) 7.7 6 5.7 6 0.93 (0.81, 1.08) 1.02 (0.85, 1.23) 0.79 (0.62, 1.01) 0.043

Fruit and nuts (g/d) 377.1 6 204.1 204 1.02 (0.89, 1.17) 1.00 (0.84, 1.18) 1.07 (0.85, 1.33) 0.905

Dairy products (g/d) 214.9 6 144.7 144 0.98 (0.85, 1.12) 0.95 (0.78, 1.15) 0.98 (0.80, 1.20) 0.818

Cereals (g/d) 144.7 6 55.3 55 1.00 (0.86, 1.16) 1.04 (0.85, 1.27) 0.94 (0.76, 1.18) 0.283

Meat and meat products (g/d) 93.7 6 44.6 44 0.95 (0.82, 1.11) 1.05 (0.88, 1.25) 0.83 (0.65, 1.06) 0.125

Fish and shellfish (g/d) 21.8 6 15.7 16 1.08 (0.95, 1.21) 1.22 (1.05, 1.44) 0.94 (0.78, 1.15) 0.019

Olive oil (g/d) 44.2 6 21.7 21 0.93 (0.80, 1.08) 1.00 (0.82, 1.22) 0.85 (0.69, 1.06) 0.106

Monounsaturated lipids (g/d) 46.7 6 17.3 17 0.90 (0.74, 1.09) 0.99 (0.77, 1.26) 0.77 (0.57, 1.04) 0.078

Saturated lipids (g/d) 26.7 6 11.2 11 1.02 (0.84, 1.23) 0.99 (0.78, 1.25) 1.03 (0.74, 1.43) 0.616

Monounsaturates:saturates 1.9 6 0.5 0.5 0.92 (0.81, 1.04) 0.99 (0.82, 1.20) 0.88 (0.75, 1.03) 0.271

Ethanol (g/d) 3.5 6 6.6 5 0.99 (0.89, 1.10) 0.98 (0.85, 1.13) 1.01 (0.86, 1.17) 0.868

Energy intake (kcal/d) 1867.8 6 568.3 568 1.03 (0.90, 1.17) 1.10 (0.93, 1.30) 0.93 (0.76, 1.14) 0.260

1 HRs were derived from Cox regression.2 Rounded number close to the SD of the daily intake of the respective dietary variable.3 Adjusted for age at enrollment (categorically as ,45, 45–54, or �55 y), educational level (categorically as none/elementary, secondary, or university

degree/higher), smoking status at recruitment (categorically as never, former, or current), BMI (ordered as quintiles), height (ordered as quintiles), metabolic

equivalents of task hours per day (ordered as quintiles), energy intake (ordered as quintiles), age of menarche (�11, 12, 13, or �14 y; ordered), parity (yes or

no), age at first delivery (continuous and centered around the mean of parous women), menopausal status (pre-/perimenopausal or postmenopausal), age at

menopause (continuous and centered around the mean of postmenopausal women), hormone replacement therapy (yes or no), and an interaction term for the

BMI by menopausal status.4 Adjusted for the same factors as in footnote 3 but without variables denoting menopausal status, age at menopause, and the interaction term for BMI by

menopausal status.5 Adjusted for the same factors as in footnote 3 but without variables denoting menopausal status and the interaction term for BMI by menopausal status.6 P for interaction by menopausal status was derived from a likelihood ratio test.

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Page 5: Mediterranean diet and breast cancer

were very similar [per 2-point increment: overall, HR = 0.88,95% CI (0.74, 1.04); pre-/perimenopausal, HR = 1.03, 95% CI(0.81, 1.32); and postmenopausal, HR = 0.76, 95% CI (0.60,0.96)]. Exclusion of ethanol intake from the score, but con-trolling for it in the analysis, did not lead to a further reductionof hazard ratios.

DISCUSSION

In a cohort of women in Greece, we used a simple, previouslydeveloped (4), and frequently used (8) dietary score to evaluateadherence to the traditional Mediterranean diet and found evi-dence that conformity to this dietary pattern may be associatedwith reduced breast cancer risk among postmenopausal women.There was no evidence for an association among premenopausalwomen, and the interaction term for menopausal status by MDSin relation to breast cancer risk was statistically significant (P =0.05). Above and beyond the statistical evidence, differences inthe epidemiologic profile of pre- and postmenopausal breastcancer, and the strongest influence of genetic and early life in-fluences on premenopausal disease (22, 23) convey an elementof biological plausibility to a differential association of diet withpre- and postmenopausal disease.

We identified 2 other studies in the literature that evaluatedconformity to the Mediterranean diet in relation to breast cancerrisk. In a large cohort study of postmenopausal women in theUnited States, Fung and colleagues (11) reported a significantinverse association for estrogen receptor–negative breast can-cer, but no association with estrogen receptor–positive tumors.In a population-based case-control study among Asian-Americanwomen, again in the United States, Wu and colleagues (24)reported a significant inverse association between conformity tothe Mediterranean dietary pattern and breast cancer risk. From anecologic perspective, Mediterranean countries in the 1960s andthe 1970s, when the traditional Mediterranean diet was omni-present in the region, had considerably lower breast cancermortality rates when compared with other European countries orthe United States. Indeed, in Greece mortality from breast cancerin the 1960s was ’8 per 100,000 women years, whereas in theUnited States it was almost 3 times as high (25). Finally, therehave been several studies, all in Mediterranean countries,reporting an inverse association of breast cancer risk witholive oil, which is central to the traditional Mediterranean diet(26–29).

Several physiologic mechanisms have been proposed andsupportive evidence has been provided for a possible protectiveeffect of the Mediterranean diet against breast cancer risk. It hasbeen reported that a traditional Mediterranean diet significantlyreduces endogenous estrogens (30) and contributes to increasedlevels of sex hormone binding globulin (24). The Mediterraneandiet is rich in flavonoids (in particular flavones, flavonols, andresveratrol), substances with important antioxidant properties(31), and low in ruminant animal-derived phytanic acid, which issuspected to contribute to the occurrence of several forms ofcancer (32). It has also been reported that the lipid composition ofthis diet may have inhibitory potential on HER2 (erB-2) ex-pression (33). Lastly, squalene (an important compound of oliveoil and the typical added oil in the Mediterranean diet) has beenreported to protect against oxidative DNA damage in normalmammary cells (34).

The apparent association of the traditional Mediterraneandiet with postmenopausal breast cancer risk is of modest, butnot negligible, strength. On the basis of the data in Table 3, itcan be calculated (35) that overall’10% of breast cancer casesin this population could be avoided if all women shifted theirdiet toward one adhering more closely to the Mediterraneandietary pattern (ie, corresponding to a score of �6). When thecalculation was limited to postmenopausal women, this frac-tion was considerably higher but very unstable. Neverthelessother factors may also have contributed to the lower incidence ofbreast cancer in Greece compared with other Western countries,notably the fact that the prevalence of use of exogenous hor-mones, which have been documented to increase the risk ofbreast cancer (36, 37), has always been very low in the Greekpopulation (38).

Strengths of our study are its cohort design, the use of a val-idated food-frequency questionnaire (16), the relatively longfollow-up, and undertaking of the study in a country in whicha substantial fraction of the population still adheres to the tra-ditional Mediterranean diet. Among its limitations are its modestsize, lack of information on receptor status, and the fact thatmenopausal status was ascertained at enrollment and not at thetime of diagnosis of the cases, which is likely to have introducedsome misclassification. In conclusion, we have found evidencethat conformity to the traditional Mediterranean diet may beassociated with lower breast cancer risk among postmenopausalwomen and could explain, in part, the lower incidence of thisdisease in Mediterranean countries.

TABLE 3

Hazard ratios (95% CIs) for incident breast cancer (240 cases) in relation to Mediterranean Diet Score among 14,807 women of the Greek European

Prospective Investigation into Cancer and Nutrition (EPIC) cohort study1

Mediterranean Diet Score

0–3 4–5 6–9 2-Point increment P

Overall2 Referent 0.93 (0.69, 1.25) 0.84 (0.59, 1.20) 0.88 (0.75, 1.03) 0.12

Excluding first year of follow-up Referent 0.93 (0.69, 1.26) 0.83 (0.57, 1.20) 0.87 (0.74, 1.03) 0.11

By menopausal status3

Pre-/perimenopausal (n = 6534)4 Referent 0.88 (0.56, 1.39) 1.13 (0.69, 1.85) 1.01 (0.80, 1.28) 0.91

Postmenopausal (n = 8273)5 Referent 0.96 (0.65, 1.42) 0.59 (0.34, 1.03) 0.78 (0.62, 0.98) 0.03

1 Hazard ratios were derived from Cox regression.2,4,5 Adjusted for the same factors indicated in Table 2: 2for overall analysis, 4for premenopausal women, 5for postmenopausal women.3 P for interaction = 0.05 (likelihood ratio test).

624 TRICHOPOULOU ET AL

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The authors’ responsibilities were as follows—AT: principal investigator

of the Greek EPIC cohort and initiated the study; CB: contributed to epide-

miologic design and undertook statistical analysis; PL: contributed to epide-

miologic design and statistical analysis; and DT: served as the epidemiologic

consultant. All of the authors contributed to drafting the manuscript. None of

the authors had any conflicts of interest to declare.

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