Association between area - and individual - level socio-economic factors with glycated haemoglobin: evidence from a Portuguese population-based study

Aims: This study aims to estimate the associations between area-level deprivation and individual-level socio-economic factors, as well as their interaction, with glycated haemoglobin (HbA_1c) levels. Methods: We conducted a gamma multilevel regression analysis using individual-level data from the Portuguese National Health Examination Survey and a deprivation index built through factor analysis, at municipality level, with census variables. Results: Living in a municipality with high material deprivation and having a low level of education were independently associated with an increase of 2.3% (95% confidence interval [CI] 0.6, 4.0) and of 1.6% (95% CI 0.6, 2.7) in the mean levels of HbA_1c, respectively. The interaction between area material deprivation and individual-level education was not associated with the levels of HbA_1c (0.5%, 95% CI −1.3, 2.3). Conclusions: Our findings support the collective resources model that argues that people in less deprived areas have better health because there are more collective resources. The results suggest that to reduce socio-economic inequalities associated with the levels of HbA_1c and, consequently, with diabetes, will require attention to the area material deprivation and individual-level education. Upstream social determinants of health are thus highlighted.