Vitamin D Supplementation in Patients With Type 2 Diabetes: The Vitamin D for Established Type 2 Diabetes (DDM2) Study
What this study found
Overall, daily vitamin D3 did not improve beta-cell function or glycemic control compared with placebo in adults with well-controlled type 2 diabetes. The primary insulin secretion outcome was unchanged: ISR fasting was 20.700 vs 21.684 and ISR total was 622.88 vs 778.41, with P = 0.896 and P = 0.952, respectively; ISI-Matsuda and ISSI-2 were also not significantly different. HbA1c did not differ through 48 weeks (week 48: 0.2 vs 0.2; P = 0.866). A transient HbA1c reduction was seen in the lifestyle-only subgroup at week 24 (-0.1 vs 0.3; P = 0.034), but it was not sustained. The intervention…
- Study & population
- Randomized, placebo-controlled trial in US adults with stable, well-controlled type 2 diabetes recruited at Tufts Medical Center in Boston and the Veterans Affairs Medical Center in Cincinnati.
- Intervention
- Oral vitamin D3 (cholecalciferol) 4000 IU/day was given daily for 48 weeks.
- Key limitation
- The trial was relatively small and conducted in a specific population with already well-controlled diabetes, limiting generalizability.
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Open PDFOriginal abstract
Abstract Context Observational data support a role for vitamin D in type 2 diabetes, but evidence from trials is inconclusive. Objective To evaluate the effect of vitamin D supplementation on β-cell function and hemoglobin A1c (HbA1c) in patients with well-controlled type 2 diabetes. Design Double-blind, randomized, placebo-controlled clinical trial. Setting Tufts Medical Center, Boston, MA; VA Medical Center, Cincinnati, OH. Participants A total of 127 patients (mean age, 60 years) with stable (HbA1c ≤7.5%) diabetes managed with lifestyle only or lifestyle plus metformin. Intervention Subjects were given 4000 units of vitamin D3 (cholecalciferol) daily or placebo for 48 weeks. Main Outcome Measure Insulin secretion rate (ISR) was estimated from peripheral plasma C-peptide levels after a 3-hour 75-g oral glucose tolerance test done at baseline and week 24. Changes in HbA1c were assessed at 16, 24, 36, and 48 weeks. Results Baseline mean plasma 25-hydroxyvitamin D [25(OH)D] concentration was 26.6 ng/mL, mean HbA1c was 6.6%, and 78% of patients were on metformin. At week 24, mean 25(OH)D changed by 20.5 and −1.6 ng/mL in the vitamin D and placebo groups, respectively (P < 0.001). The vitamin D and placebo groups did not differ in change in ISR or HbA1c. Among patients treated with lifestyle only (n = 28), vitamin D supplementation reduced HbA1c compared with placebo (−0.1% vs 0.3%, respectively; P = 0.034) at week 24. This result was not observed at the other time points and could be due to chance. Conclusion Vitamin D3 at 4000 IU/d did not change ISR or HbA1c in patients with well-controlled type 2 diabetes on metformin not selected for vitamin D deficiency.