Education, income, occupation, and the 34-year incidence (1965-99) of Type 2 diabetes in the Alameda County Study

Background: Lower socioeconomic position (SEP) is related to higher prevalence of Type 2 diabetes, yet little is known about the relationship of SEP with incident diabetes. Methods: The association between SEP, measured by self-reported education, income, and occupation, and Type 2 diabetes incidence was examined in a community sample of 6147 diabetes-free adults from Alameda County, CA. Cox proportional hazards models estimated the effect of baseline (1965) and time-dependent (value changes over time) measures of SEP on incident diabetes over a 34-year study period (1965-99). Demographic confounders (age, gender, race, and marital status) and potential components of the causal pathway (physical inactivity, smoking, alcohol consumption, body composition, hypertension, depression, and health care access) were included as fixed or time-dependent covariates. Results: Education, income, and occupation were associated with increased diabetes risk in unadjusted models. In baseline models adjusted for demographics, respondents with <12 years of education had 50% excess risk compared with those with more education [hazard ratio (HR) = 1.5, 95% confidence interval (95% CI) 1.11-2.04], but income and occupation were no longer significantly associated with increased risk. Further adjustment minimized the significance of all associations. Time-dependent effects were consistently elevated for low education and male blue-collar occupation, but non-significant after full adjustment (HR = 1.1, 95% CI 0.79-1.47 and HR = 1.3, 95% CI 0.91-1.89, respectively). Conclusions: Socioeconomic disadvantage, especially with low educational attainment, is a significant predictor of incident Type 2 diabetes, although associations were largely eliminated after covariate adjustment. Obesity and overweight appear to mediate these associations.