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Aims: To study the effects of metformin, as compared to placebo, on serum levels of vitamin D (25‐hydroxyvitamin D [25(OH)D]) in patients with advanced type 2 diabetes. Materials and Methods: In the HOME trial, a randomized placebo‐controlled trial, 390 insulin‐treated patients with type 2 diabetes were treated with 850 mg metformin or placebo thrice daily for 52 months. In a post‐hoc analysis, we examined changes in the combined levels of 25(OH)D2 and 25(OH)D3 at 4 and 16 months during the study. Results: Mean combined 25(OH)D at baseline was 68.2 nmoL/L (95% confidence interval [CI]: 65.5‐71.1). In mixed model analysis, metformin, as compared to placebo, had no effect on 25(OH)D levels during 16 months (coefficient: 1.002 per month, multiplicative model; 95% CI: 0.998‐1.006, P = .30). Metformin was associated with a small increase of 25(OH)D2 (coefficient: 1.012 per month; 95% CI: 1.003‐1.021, P = .008). However, 25(OH)D2 is only a very small fraction (3%) of 25(OH)D. Seasonal variation had the biggest impact on 25(OH)D levels. Vitamin B12 levels were not associated with the levels of 25(OH)D. Conclusion: Metformin had no effect on serum 25(OH)D during 16 months in the setting of a clinical randomized controlled trial in patients with type 2 diabetes. Our results show that metformin doesn't lead to vitamin D deficiency. [ABSTRACT FROM AUTHOR]

Metformin prevents weight gain in patients with type 2 diabetes ( T2D). However, the mechanisms involved are still unknown. In this post hoc analysis of the HOME trial, we aimed to determine whether metformin affects energy intake. Patients with T2D were treated with 850 mg metformin or received placebo added to insulin (1-3 times daily) for 4.3 years. Dietary intake was assessed at baseline, after 1 year and after 4.3 years, according to the dietary history method. Among the 310 included participants, 179 (93 placebo, 86 metformin) completed all 3 dietary assessments. We found no significant difference in energy intake after 4.3 years between the groups (metformin vs placebo: −31.0 kcal/d; 95% CI, -107.4 to 45.4; F-value, 1.3; df = 415; P = .27). Body weight in placebo users increased significantly more than in metformin-users during 4.3 years (4.9 ± 4.9 vs 1.1 ± 5.2 kg; t test: P ≤ .001). Linear mixed models did not show a significant effect of energy intake as explanation for the difference in weight gain between the groups ( F-value, 0.1; df = 1; P = .82). In conclusion, the prevention of weight gain by metformin cannot be explained by reduced energy intake. [ABSTRACT FROM AUTHOR]