mrc/cso social and public health sciences unit socioeconomic gradients in coronary heart disease -...

MRC/CSO Social and Public Health Sciences Unit

Socioeconomic gradients in coronary heart disease - the relative role of lifestyle

Linsay Gray1, Julie Armstrong2, Yvonne Brogan2, Andrea Sherriff3, Catherine Bromley4, Alastair H Leyland1

1 MRC/CSO Social and Public Health Sciences Unit, Glasgow, UK2 School of Life Sciences, Glasgow Caledonian University, Glasgow, UK3 Department of Dentistry and Medicine, University of Glasgow, Glasgow, UK4 Scottish Centre for Social Research, Edinburgh, UK

Royal Statistical Society Edinburgh local group talk, 15 November 2011


Background

• CHD strongly correlated with SES • Lifestyle factors impact on health and are also linked

with SES • Thus may drive the CHD-SES associations• Individual and combined lifestyle contributions to such

inequalities not well quantified


Aims

• To quantify contributions of lifestyle factors to social inequalities in CHD

• Individual and combined


Data

6,060 participants >16 years in 2003 Scottish Health Survey (60% response) providing data on

also consenting to linkage of mortality and hospital records ‘til 2008

• SES (social class)

• Smoking status (current and previous)• Physical activity levels• Diet (quality index) next slide

• BMI and • Alcohol consumption (weekly intake)

• CHD death or admission


Diet quality index - DQI

• >20 foods• Summary measure scores based on recommendations • types and frequency

• Fish, red meat and products• Starchy foods• High fibre foods• Sugary foods• Fatty foods• Fruit and vegetables • (Alcohol)

Armstrong, J. et al. (2009).


Statistical methods

• Cox proportional hazards regression1: Ascertain prediction of CHD event by SES adjusting for

age only2: Investigate degree of attenuation of the association of

CHD with SES by lifestyle

• Assess using Relative Index of Inequality (RII)


Relative Index of Inequality (RII)

• Commonly used measure of extent to which occurrence of an outcome - such as CHD - varies with risk factors such as SES

• Measures relative disparity by summarizing relative risk for extremes

• Calculation• Rank values• Scale ranks from 0 to 1• Analyse as a covariate in usual way• Obtain estimates for a “one unit increase”


CHD and baseline social class data

• 35,523 person-years of follow-up• 213/6,060 (4%) CHD events; including 59 (28%) deaths;

442

1,937

880

1,554

905

342

0

500

1000

1500

2000

I –Professional

II- Managerial IIIN – SkilledNon-manual

IIIM - SkilledManual

IV – Semi-skilled

V – Unskilled


Lifestyle factors

Mean SDDietary quality index 52 17 BMI 27 kg/m2 5.3 kg/m2

Alcohol units/week14 units 21 units

0

500

1,000

1,500

2,000

2,500

3,000

Never smoked Ex-occasional Ex-regular Current smoker0

500

1,000

1,500

2,000

2,500

Low Medium High


0.0

2.0

4.0

6.0

8D

ensi

ty

0 50 100 150 200 250(D) Total Units of alcohol/week

Alcohol distribution


Natural log of alcohol distribution

0.2

.4.6

Den

sity

-4 -2 0 2 4 6dratingRf2ln


Lifestyle factor associations with SES and CHD

SES CHDSmoking status all p<0.001

NeverEx-occ 0.287Ex-reg <0.001Current 0.003

Physical activity Low

Medium <0.001High <0.001

Dietary quality index 0.50BMI 0.011ln(Alcohol units/week) 0.004


Number breakdown

Social class deaths n

Professional 9 442

Intermediate 56 1937

Skilled (non-manual) 21 880

Skilled (manual) 71 1554

Partly Skilled 38 905

Unskilled 18 342

All 213 6060


CHD and social class Cox regression results

0.00

1.00

2.00

3.00

4.00

5.00


Proportional hazards? - log-log plot

34

56

78

-ln[

-ln(S

urvi

val P

rob

abili

ty)]

-4 -2 0 2ln(analysis time)

schrpg2 = 1 schrpg2 = 2


Proportional hazards check

0.0

00

.25

0.5

00

.75

1.0

0

0 2 4 6analysis time


Kaplan-Meier survival estimates


Proportional hazards check

0.0

00

.01

0.0

20

.03

0.0

40

.05

0 2 4 6analysis time


Nelson-Aalen cumulative hazard estimates

p=0.539


CHD and social class Cox regression results

Social class deaths n HR 95% CI

Non-manual 86 3,173 1.00

Manual 127 2,674 1.60 1.21 2.10

RII 213 6,060 2.10 1.29 3.43

Sex interaction p = 0.254


CHD and social class Cox regression results- attenuation by smoking

%

Social class deaths n HR 95% CI HR 95% CI decrease

Non-manual 86 3,173 1.00 1.00

Manual 127 2,674 1.60 1.21 2.10 1.46 1.11 1.93 22

RII 213 6,060 2.10 1.29 3.43 1.77 1.07 2.90 31


CHD and social class Cox regression results- attenuation by physical activity

%


Non-manual 86 3,173 1.00 1.00

Manual 127 2,674 1.60 1.21 2.10 1.53 1.16 2.02 11

RII 213 6,060 2.10 1.29 3.43 1.93 1.18 3.16 15


CHD and social class Cox regression results- attenuation by diet

%


Non-manual 86 3,173 1.00 1.00

Manual 127 2,674 1.60 1.21 2.10 1.53 1.16 2.03 10

RII 213 6,060 2.10 1.29 3.43 1.95 1.18 3.21 14


CHD and social class Cox regression results- attenuation by BMI

%


Non-manual 86 3,173 1.00 1.00

Manual 127 2,674 1.60 1.21 2.10 1.57 1.20 2.07 4

RII 213 6,060 2.10 1.29 3.43 2.04 1.24 3.33 6


CHD and social class Cox regression results- attenuation by alcohol

%


Non-manual 86 3,173 1.00 1.00

Manual 127 2,674 1.60 1.21 2.10 1.59 1.21 2.09 1

RII 213 6,060 2.10 1.29 3.43 2.08 1.27 3.40 2


CHD and social class Cox regression results- attenuation by all lifestyle factors

%


Non-manual 86 3,173 1.00 1.00

Manual 127 2,674 1.60 1.21 2.10 1.37 1.03 1.82 37

RII 213 6,060 2.10 1.29 3.43 1.53 0.92 2.56 52


Strengths and limitations

• Reasonable sample size• Covers the (home-dwelling) general population of

Scotland• High linkage consent (>90%)• Range of covariates

• Emigration – lost to follow-up but low levels• Excludes those living in communal establishments

• e.g. • prisons• residential care

• Bias from survey response (67% household; 60% individual)


Conclusions

• Adjusting for lifestyle factors attenuates association by over 50%

• Individually, greatest impacts made by smoking (31%), physical activity (15%) and diet (14%)

• Little impact of BMI and alcohol• Valuable insight for tackling socio-economic health

inequalities• Importance of physical activity and healthy eating as

well as smoking• What else?

• Structural/environmental factors


Acknowledgements

• Data were provided by • ISD

• Funding was provided by the Chief Scientist Office for Scotland

• Thanks to Joan Corbett of ScotCen for help with data queries


• Thank you for your attention

• Contact me on [email protected] for further information

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