Health inequalities in type 2 diabetes: contributions of exposures in the residential environment

BACKGROUND: People with lower socioeconomic position (SEP) have higher risk of type 2 diabetes (T2D). Besides genetic predisposition, the exposome shapes this risk. This includes exposures in the residential environment. We explored the relationships between SEP, the residential food environment, walkability, greenspace, and T2D. METHODS: Cross-sectional and longitudinal data from 9188 participants were analyzed. Prevalent T2D was measured by an oral glucose tolerance test. Incident T2D was self-reported in annual follow-up questionnaires. Education, income, and occupation were measured as indicators of SEP. The residential environment was operationalized by address level Food Environment Healthiness Index (FEHI), number of fast-food outlets (FF), walkability index (WI), and proportion of greenspace (GS). Logistic regression and survival analyses were used to model the associations between SEP, the environment and T2D. The proportion of mediation of the association between SEP and T2D was estimated in a causal mediation analysis using a simulation approach. RESULTS: Over a median follow-up of 6.2 years, 207 incident cases were identified. Lower SEP was associated with higher risk of T2D. Hazard ratios (HR) were 2.0 (95%CI 1.6-2.6), 1.8 (1.4-2.3) and 1.8 (1.2-2.6) for an interquartile range decrease (IQR) of education, income, and occupation, respectively. HRs for IQR changes of the environmental factors were: FEHI 1.2 (1.0-1.4), FF 0.9 (0.8-1.0), WI 1.2 (1.0-1.6) and GS 1.2 (1.0-1.4). Regression on prevalent T2D yielded similar results. Lower SEP was associated with a less healthy environment (e.g., FEHI -0.08 (-0.10--0.06) for education). Environmental exposures mediated between 0.3% (-8.6-8.6) and 8.5% (2.3-27.4) of the longitudinal associations. CONCLUSIONS: Lower SEP was associated with prevalent and incident T2D. People with lower SEP lived in a slightly less healthy residential environment. Some of the SEP-T2D association could be mediated by the environment. KEY MESSAGES: • A less healthy residential food environment, lower walkability and less green space might mediate some of the association between SEP and T2D. • More research is needed to clarify the extent to which environmental pathways contribute to health inequalities.