Insulin and risk of diabetic retinopathy in patients with type 2 diabetes mellitus: data from a meta-analysis of seven cohort studies

Background: Type 2 diabetes mellitus (T2DM) is a chronic incurable disease associated with multi-systemic complications. The chronic complications related to T2DM induce growing burden to the national health system. Diabetic retinopathy (DR) is the most serious ocular complication associated with T2DM and one of the leading causes of secondary blindness. The association between insulin use and DR risk has also been reported in different studies. Methods: In order to obtain more informative results on the relationship between insulin intake and risk of DR and to take into account more recent evidence, we conducted this meta-analysis by including all available relevant cohort studies. A systemic literature search was performed via electronic databases inclu-apding Pubmed and EMBASE to identify all available relevant studies until February 2014. A total of seven cohort studies were included in this meta-analysis. In this meta-analysis, we conducted a rigorous search of all available published cohort studies to quantify the possible association between insulin use and incidental DR in individuals with type 2 diabetes. Results: Although major heterogeneity existed in this study, the significant association between insulin use and risk of DR was detected. The subgroup analyses by study design, region, data source and adjustment of HbA1c generated similar results. Also, when the DM duration was adjusted, no result was reported with significant difference. Conclusion: The results of this meta-analysis helps to better explore the role of insulin use in DR risk development. Meanwhile, our results are statistically robust and yield important conclusions. The underlying mechanism by which insulin use increases DR risk should be explored in future in vitro and in vivo studies. Additional large-scale, well-designed studies with sufficient data are needed to confirm our findings.