Socio-economic status and HbA1c in type 2 diabetes: A systematic review and meta-analysis.

Up until now, differences in HbA1c levels by socio-economic status (SES) have been identified, but not yet quantified in people with type 2 diabetes. The aim of this study was therefore to assess the difference in HbA1c levels between people with type 2 diabetes of different SES in a systematic review and meta-analysis. A systematic literature search was conducted in MEDLINE, Embase, Ebsco, and the Cochrane Library until January 14, 2018. Included studies described adults with type 2 diabetes in whom the association between SES and HbA1c levels was studied. Studies were rated for methodological quality and data were synthesized quantitatively (meta-analysis) and qualitatively (levels of evidence), stratified for type of SES variable, i.e., education, income, deprivation, and employment. Fifty-one studies were included: 15 high, 27 moderate, and 9 of low methodological quality. Strong evidence was provided that people of low SES have higher HbA1c levels than people of high SES, for deprivation, education, and employment status. The pooled mean difference in HbA1c levels between people of low and high SES was 0.26% (95% CI, 0.09-0.43) or 3.12 mmol/mol (95% CI, 1.21-5.04) for education and 0.20% (95% CI, -0.05 to 0.46) or 2.36 mmol/mol (95%CI, -0.61 to 5.33) for income. In conclusion, our systematic review and meta-analysis showed that there was an inverse association between SES and HbA1c levels in people with type 2 diabetes. Future research should focus on finding SES-sensitive strategies to reduce HbA1c levels in people with type 2 diabetes.