Background Current evidence linking socioeconomic factors to incident Type 2 Diabetes Mellitus (T2DM) in older populations is conflicting. We investigated the prospective association of individual socioeconomic position and neighbourhood-level socioeconomic deprivation with incident T2DM in older British men, and examined possible underlying factors.
Methods A socially-representative cohort of 3487 men, aged 60–79 years in 1998–2000, from 24 British towns was followed-up for 14 years for incident cases of T2DM. Individual socioeconomic position was based on social class derived from the longest-held occupation in middle-age, and was categorised into non-manual and manual groups. Neighbourhood-level socioeconomic deprivation was based on national Index of Multiple Deprivation (IMD) quintiles; a composite score of neighbourhood-level factors (income, employment, education, disability, crime, housing and living environment), with a higher score indicating greater deprivation. Follow-up on type 2 diabetes was obtained from reviews of general practitioner records and self-reported from questionnaires. Cox proportional hazards models were used to obtain hazard ratios (HR) and 95% CI for incident diabetes according to social class and IMD quintiles. Prevalent cases of diabetes at baseline were excluded from the analyses.
Results During the follow-up of 14 years, there were 289 incident cases of T2DM (7.1 per 1000 person-years). Diabetes risk increased from higher to lower social class groups and from IMD quintile 1 (least deprived) to quintile 5 (most deprived) (P for trend=0.001). Compared with non-manual social class groups, age-adjusted HR for manual groups was 1.58 (95%CI 1.24–2.01) – this was largely attenuated (1.38; 95% CI 1.08–1.76) on adjustment for body mass index (BMI); adjustment for blood pressure, smoking, alcohol, physical activity, diet, medication and family history resulted in little attenuation while further adjustment for triglyceride levels attenuated the association. Compared with IMD quintile 1, the risk of incident T2DM was highest in IMD quintile 4 (HR=1.79; 95% CI 1.24–2.54). This largely attenuated on adjustment for BMI (HR=1.46; 95% CI 1.02–2.10), and became non-significant after adjustment for lifestyle factors (smoking, alcohol, physical activity and diet).
Conclusion Manual social class and neighbourhood-level socioeconomic deprivation was associated with an increased risk of T2DM in older British men. For social class this was mostly explained by BMI and triglycerides. For neighbourhood-level socioeconomic deprivation it was largely explained by BMI and lifestyle factors. Our results support the need for public health initiatives specifically targeting obesity as a means towards reducing socioeconomic inequalities in type 2 diabetes in later life.
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