Diabetes severity and the risk of depression: A nationwide population-based study

Background: In consideration of the substantial occurrence rates of diabetes mellitus (DM) and depression, it is imperative to identify patients with DM who are at an elevated risk of developing depression. Accordingly, this study aimed to examine whether the risk of depression escalated proportionally with the severity of diabetes. Methods: 2,067,017 adults diagnosed with type 2 DM, with the exception of those diagnosed with depression either before or within one year of the index date, were identified from a nationwide population -based cohort in Korea. Severity scores for DM were established based on various factors, including insulin use, DM duration of at least 5 years, use of three or more oral hypoglycemic agents, the presence of chronic kidney disease (CKD), cardiovascular diseases (CVD), or diabetic retinopathy. Each of these attributes was assigned a score of one point for diabetes severity, and their cumulative sum was defined as a diabetes severity score, ranging from 0 to 6. Results: During a median follow-up of 6.2 years, 407,047 cases of major depression were identified. Each component contributing to the DM severity score was significantly associated with an increased risk of depression (all P -values <0.001), with insulin use and the presence of CVD demonstrating the most significant correlation with depression risk. As the DM severity score increased, the risk of depression was observed to significantly escalate (P for trend <0.001). After adjusting for potential confounding variables, the hazard ratios (95% confidence intervals) of depression were 1.15 (1.14-1.16) in 1 point, 1.28 (1.27-1.29) in 2 points, 1.45 (1.43-1.47) in 3 points, 1.70 (1.67-1.73) in 4 points, 1.91 (1.84-1.98) in 5 points, and 2.01 (1.79-2.26) in 6 points, respectively. Conclusion: The results of this study indicate that diabetes severity is positively associated with an elevated risk of developing major depression. Based on these findings, it is feasible to consider targeting depression screening efforts towards individuals with higher diabetes severity scores.