Vitamin D3 supplementation not an effective defence strategy against diabetes
Supplementation with vitamin D3 at a dose of 4,000 IU per day does not significantly stave off the risk of diabetes in high-risk individuals with or without vitamin D insufficiency, according to data from the Vitamin D and Type 2 Diabetes (D2D) trial.
D2D randomized 2,423 adults free of diabetes but who met at least two of three glycaemic criteria for prediabetes (fasting plasma glucose level, 100–125 mg/dl; plasma glucose level 2 hours after a 75-g oral glucose load, 140–199 mg/dl; and HbA1c level, 5.7–6.4 percent) to receive either 4,000 IU per day of vitamin D3 (n=1,211) or placebo, regardless of the baseline serum 25-hydroxyvitamin D level.
By month 24, the mean serum 25-hydroxyvitamin D level increased in the vitamin D group (from 27.7 ng/ml at baseline to 54.3 ng/ml) but remained stable in the placebo group (from 28.2 ng/ml at baseline to 28.8 ng/ml).
Over a median follow-up of 2.5 years, the primary outcome of new-onset diabetes occurred in 293 participants in the vitamin D group and 323 in the placebo group, resulting in incidence rates of 9.39 and 10.66 events per 100 person-years, respectively. Cox analysis showed that vitamin D supplementation did not lead to a significant reduction in the risk of incident diabetes (hazard ratio, 0.88, 95 percent CI, 0.75–1.04; p=0.12).
The incidence of adverse events (AEs) such as hypercalcaemia, fasting urine calcium:creatinine ratio of >0.375, low estimated glomerular filtration rate and nephrolithiasis, was comparable between the two groups. Overall, AEs led to trial withdrawal in 47 participants (3.9 percent) in the vitamin D group vs 37 (3.1 percent) in the placebo group (difference, 0.8 percentage points).