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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
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
Aims
• To quantify contributions of lifestyle factors to social inequalities in CHD
• Individual and combined
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
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).
MRC/CSO Social and Public Health Sciences Unit
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)
MRC/CSO Social and Public Health Sciences Unit
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”
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
Natural log of alcohol distribution
0.2
.4.6
Den
sity
-4 -2 0 2 4 6dratingRf2ln
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
CHD and social class Cox regression results
0.00
1.00
2.00
3.00
4.00
5.00
MRC/CSO Social and Public Health Sciences Unit
CHD and social class Cox regression results
0.00
1.00
2.00
3.00
4.00
5.00
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
Proportional hazards check
0.0
00
.25
0.5
00
.75
1.0
0
0 2 4 6analysis time
schrpg2 = 1 schrpg2 = 2
Kaplan-Meier survival estimates
MRC/CSO Social and Public Health Sciences Unit
Proportional hazards check
0.0
00
.01
0.0
20
.03
0.0
40
.05
0 2 4 6analysis time
schrpg2 = 1 schrpg2 = 2
Nelson-Aalen cumulative hazard estimates
p=0.539
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
CHD and social class Cox regression results- attenuation by physical activity
%
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 1.53 1.16 2.02 11
RII 213 6,060 2.10 1.29 3.43 1.93 1.18 3.16 15
MRC/CSO Social and Public Health Sciences Unit
CHD and social class Cox regression results- attenuation by diet
%
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 1.53 1.16 2.03 10
RII 213 6,060 2.10 1.29 3.43 1.95 1.18 3.21 14
MRC/CSO Social and Public Health Sciences Unit
CHD and social class Cox regression results- attenuation by BMI
%
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 1.57 1.20 2.07 4
RII 213 6,060 2.10 1.29 3.43 2.04 1.24 3.33 6
MRC/CSO Social and Public Health Sciences Unit
CHD and social class Cox regression results- attenuation by alcohol
%
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 1.59 1.21 2.09 1
RII 213 6,060 2.10 1.29 3.43 2.08 1.27 3.40 2
MRC/CSO Social and Public Health Sciences Unit
CHD and social class Cox regression results- attenuation by all lifestyle factors
%
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 1.37 1.03 1.82 37
RII 213 6,060 2.10 1.29 3.43 1.53 0.92 2.56 52
MRC/CSO Social and Public Health Sciences Unit
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)
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
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
MRC/CSO Social and Public Health Sciences Unit
• Thank you for your attention
• Contact me on l.gray@sphsu.mrc.ac.uk for further information
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