Vitamin D supplements have no clinically meaningful effect in people at high risk of type 2 diabetes

They did, however, find a significant increase in both lower back and hip bone mineral densities among those taking eldecalcitol compared with placebo.No significant difference in serious adverse events was seen between the two groups.

The researchers acknowledge some uncertainties, such as whether the dose of eldecalcitol used was appropriate for preventing diabetes, and whether the results apply to all ethnicities. Nevertheless, this was a large trial with regular follow-up and high adherence to treatment, suggesting that the findings are robust.

As such, they say: “Although treatment with eldecalcitol did not significantly reduce the incidence of diabetes among people with pre-diabetes, the results suggested the potential for a beneficial effect of eldecalcitol on people with insufficient insulin secretion.” And they call for further research to determine whether vitamin D is beneficial to people with pre-diabetes.

This new trial was well conducted and results are consistent with two other recent trials, says Tatiana Christides at Queen Mary University of London in a linked editorial.However, several questions remain, she writes, including whether vitamin D supplementation may be more effective for particular populations, and whether longer duration of treatment or younger age at initiation might be more beneficial.

Until further data are available from high quality randomized trials, she suggests healthcare professionals “should continue to discuss with patients the musculoskeletal health benefits of vitamin D and support them to achieve and maintain lifestyle changes that, although challenging to sustain, are known to decrease development of type 2 diabetes.”