Vitamin D status and its association with diabetic complications in type 2 diabetes mellitus: A case-control study

Background: Vitamin D deficiency remains as a significant public health challenge, even in sun-rich countries like India. Emerging evidence indicates that vitamin D plays a critical role in the pathophysiology of various chronic conditions, including type 2 diabetes mellitus (T2DM). Aim: Our study aims to examine the association between vitamin D deficiency and diabetic complications. Methods: This case-control study was conducted at a south Indian tertiary care facility between August 2023 and August 2024. The medical records of patients with T2DM admitted to the Department of Medicine between 2017 and 2022, with recorded vitamin D levels, were included. Patients with diabetic complications were enrolled as cases (n = 873), and those without any complications (n = 566) served as controls. The association between vitamin D deficiency and diabetic complications was determined using multivariate logistic regression, expressed as odds ratios (OR) with 95% confidence intervals (CI) using R version 4.4.1. Results: Multivariate logistic regression indicated that vitamin D deficiency was significantly associated with the development of diabetic complications, specifically neuropathy (adjusted OR (AOR) = 4.09, 95% CI 2.34-7.63, p < 0.001), nephropathy (AOR = 5.23, 95% CI 2.72-10.85, p < 0.001), retinopathy (AOR = 2.52 95% CI 1.44-4.69, p < 0.001), ischaemic heart disease (IHD) (AOR = 2.19, 95% CI 1.33-3.76, p = 0.003) and diabetic foot disease (DFD) (AOR = 2.66, 95% CI 1.34-5.91, p = 0.008). Vitamin D levels were significantly associated with factors affecting sun exposure, such as gender (p = 0.005), place of residence (p < 0.001) and type of occupation (p = 0.006). Conclusion: Vitamin D deficiency was found to be independently associated with neuropathy, nephropathy, retinopathy, IHD and DFD, indicating its possible involvement in the pathophysiology of these diabetic complications.