Socioeconomic gradient in morbidity and mortality in people with diabetes: cohort study findings from the Whitehall Study and the WHO Multinational Study of Vascular Disease in Diabetes.

OBJECTIVE: To assess whether the inverse socioeconomic mortality gradient observed in the general population persists in diabetic people.
DESIGN: The Whitehall cohort study and the London cohort of the WHO multinational study of vascular disease in diabetes.
SETTING: London.
SUBJECTS: 17,264 male civil servants (17,046 without diabetes, 218 with diabetes) aged 40-64 examined in 1967-9, and 300 people with diabetes aged 35-55 from London clinics examined in 1975-7. Both cohorts were followed up until January 1995. MAIN OUTCOME MEASURES: Mortality from all causes, cardiovascular disease, and ischaemic heart disease.
RESULTS: In both cohorts people in the lower social groups were older, had higher blood pressure, and were more likely to smoke. In the Whitehall study, the prevalence of heart disease was higher in the lowest social group compared with the highest group, by 6% among non-diabetic people (P = 0.0001) and by 14% among diabetic subjects (P = 0.02). In the WHO study proteinuria was more common in the lowest social group compared with the highest (27% v 15%, P = 0.01), as was retinopathy (54% v 48%, P = 0.5). There was a clear socioeconomic gradient in all cause mortality in both cohorts, with death rates being about twice as high in the lowest compared with the highest social groups. In the Whitehall study this gradient was similar in both diabetic and non-diabetic subjects, and it persisted for mortality from cardiovascular disease and from ischaemic heart disease. About half of the increased risk of death in the lowest social group was accounted for by blood pressure and smoking.
CONCLUSIONS: We confirm the existence of an inverse socioeconomic mortality gradient in diabetic people and suggest that this is largely due to conventional cardiovascular risk factors.