Socio-economic status and HbA_1c in type 2 diabetes: A systematic review and meta-analysis

Up until now, differences in HbA_1c 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 HbA_1c 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 HbA_1c 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 HbA_1c levels than people of high SES, for deprivation, education, and employment status. The pooled mean difference in HbA_1c 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 HbA_1c levels in people with type 2 diabetes. Future research should focus on finding SES-sensitive strategies to reduce HbA_1c levels in people with type 2 diabetes.