Effect of vitamin D supplementation on glycemic control, insulin sensitivity, and pregnancy outcomes in gestational diabetes patients undergoing dietary therapy

Abstract Objective This study aims to evaluate the effects of vitamin D supplementation on glycemic control, insulin sensitivity, and pregnancy outcomes in patients with gestational diabetes mellitus (GDM) undergoing dietary therapy. Methods This is a retrospective cohort study that included 98 patients diagnosed with GDM according to the IADPSG criteria. Patients were divided into two groups based on vitamin D supplementation: the Vitamin D group (n = 49) and the Control group (n = 49). The Vitamin D group received 400 IU of vitamin D daily until delivery. All patients followed a standardized dietary management plan. The primary outcome was the time to achieve glycemic control. Secondary outcomes included changes in HbA1c, HOMA-IR, LDL-C, hs-CRP, MDA, and pregnancy and neonatal outcomes. Propensity score matching (PSM) was used to adjust for baseline differences, and statistical analyses were performed using SPSS version 28.0. Results A total of 98 patients (49 per group) were included after propensity score matching (PSM), with similar baseline characteristics between groups (all P > 0.05), except for higher gestational edema scores in the control group (P = 0.001). The Vitamin D group achieved glycemic control faster than the control group (adjusted HR = 2.30, 95% CI 1.50–3.52, P < 0.001) and required less insulin (β = -0.11 U/kg/day, 95% CI -0.14 to -0.08, P < 0.001). Significant improvements were observed in key metabolic and inflammatory markers, including HbA1c, fasting blood glucose, 2-hour postprandial glucose, HOMA-IR, LDL-C, hs-CRP, MDA, BMI, and gestational edema score (all P < 0.001), with no change in mid-upper arm circumference. The Vitamin D group also had significantly lower risks of pregnancy complications, adverse outcomes, and neonatal issues (P < 0.05), including reduced rates of pregnancy-induced hypertension, fetal distress, and postpartum hemorrhage. Conclusion Vitamin D supplementation significantly improves glycemic control, enhances insulin sensitivity, and positively impacts pregnancy outcomes in patients with gestational diabetes. Vitamin D supplementation should be considered in the management of GDM.