Cause specific mortality, social position, and obesity among women who had never smoked: 28 year cohort study

Objective To investigate the relations between causes of death, social position, and obesity in women who had never smoked. Design Prospective cohort study. Setting Renfrew and Paisley, Scotland. Participants 8353 women and 7049 men aged 45-64 were recruited to the Renfrew and Paisley Study in 1972-6. Of these, 3613 women had never smoked and were the focus of this study. They were categorised by occupational class (I and II, III non-manual, III manual, and IV and V) and body mass index groups (normal weight, overweight, moderately obese, and severely obese). Main outcome measures All cause and cause specific mortality during 28 years of follow-up by occupational class and body mass index, using Cox proportional hazards models adjusted for age and other confounders. Results The women in lower occupational classes who had never smoked were on average shorter and had poorer lung function and higher systolic blood pressure than women in the higher occupational classes. Overall, 43% (n=1555) were overweight, 14% (n=515) moderately obese, and 5% (n=194) severely obese. Obesity rates were higher in lower occupational classes and much higher in all occupational classes than in current smokers in the full cohort. Half the women died, 51% (n=916) from cardiovascular disease and 27% (n=487) from cancer. Relative to occupational class I and II, all cause mortality rates were more than a third higher in occupational classes III manual (relative rate 1.35, 95% confidence interval 1.16 to 1.57) and IV and V (1.34, 1.17 to 1.55) and largely explained by differences in obesity, systolic blood pressure, and lung function. Similar upward gradients were seen for cardiovascular disease and respiratory disease but not for cancer. Mortality rates were highest in severely obese women in the lowest occupational classes. Conclusions Women who had never smoked and were not obese had the lowest mortality rates, regardless of their social position. Where obesity is socially patterned as in this cohort, it may contribute to health inequalities and increase pressure on health and social services serving more disadvantaged populations.