In trials that were specifically designed to test whether vitamin D reduces the rate of progression to diabetes in people with prediabetes, the risk for developing diabetes was consistently lower in the group assigned to vitamin D than in the placebo group; however, the observed differences were not statistically significant, and the reported relative risk reductions (10% to 13%) were smaller than each trial was powered to detect (25% to 36%).
We conducted a systematic review of the published literature and performed an individual participant data meta-analysis of randomized, placebo-controlled diabetes prevention trials of vitamin D among adults with prediabetes.
Three randomized trials were included (Tromsø [Norway], D2d [USA], DPVD [Japan]. Vitamin D reduced risk for diabetes by 15% in adjusted analyses with a 3-year absolute risk reduction of 3.3%. Among participants assigned to the vitamin D group who maintained an intra-trial mean blood 25-hydroxyvitamin D level of at least 50 ng/mL compared with 20 to 29 ng/mL during follow-up, vitamin D3 reduced risk for diabetes by 76% with a 3-year absolute risk reduction of 18.1%.Vitamin D increased the likelihood of regression to normal glucose regulation by 30%. There was no evidence of difference in the rate ratios for adverse events.
These results show that in adults with prediabetes, vitamin D was safe and effective in decreasing risk for diabetes.
The manuscript is published in the Annals of Internal Medicine
