Therapeutic effect of vitamin D supplementation on glycemic control in female patients with type 2 diabetes mellitus: A randomized controlled trial

This randomized controlled trial examined the relationship between therapeutic doses of vitamin D and improvement of glycemic parameters in female patients with Type 2 Diabetes Mellitus (T2DM). 27 female Libyan patients with T2DM, aged 38 - 64 years, were randomly assigned to the intervention group (n = 15) and the control group (n = 12) at the endocrinology department of Tripoli Medical Center from 2015 to 2023. The intervention group received 50,000 IU vitamin D (cholecalciferol) weekly for 12 weeks, while controls received a placebo. Serum levels of 25-hydroxyvitamin D [25(OH)D], fasting blood glucose, HbA1c, lipid profile, and calcium were measured before and after intervention. Data were analyzed using paired t-test and correlation analyses. Baseline vitamin D deficiency was prevalent: 47.0% of patients had severe deficiency, 41.0% moderate deficiency, and 11.0% had sufficient levels. After 12 weeks of supplementation, 88.0% of patients demonstrated improved vitamin D levels. Mean serum 25(OH)D increased significantly from 12.50 ± 12.40 nmol/L to 37.00 ± 10.00 nmol/L. About 80.0% of patients exhibited decreased HbA1c from 9.20 ± 1.80% to 7.90 ± 1.70%; p < 0.05. A significant inverse correlation was observed between post-intervention HbA1c and 25(OH)D levels (r = - 0.354, p = 0.04). Fasting blood glucose improved from 174.44 ± 63.77 mg/dL to 144.51 ± 38.90 mg/dL. No significant changes occurred in the control group. Weekly vitamin D supplementation for 12 weeks significantly improved vitamin D status and glycemic control in female patients with T2DM, demonstrating an inverse relationship between vitamin D and HbA1c levels. Vitamin D may be a beneficial adjunct therapy for glycemic management in vitamin D-deficient diabetic patients.