Higher vitamin D intake may be associated with a lower risk of developing type 2 diabetes in adults with prediabetes, a review of clinical trials has found.
Vitamin D is a fat-soluble vitamin available in or added to some foods, as a supplement, or produced by the body when ultraviolet rays from sunlight strike the skin.
Vitamin D has many functions in the body, including a role in insulin secretion and glucose metabolism.
Observational studies have found an association between having a low level of vitamin D in the blood and high risk for developing diabetes, the researchers said.
The team from Tufts Medical Center in the US conducted a systematic review and meta-analysis of three clinical trials comparing vitamin D supplement impacts on diabetes risk.
The researchers found that over a three-year follow-up period, new-onset diabetes occurred in 22.7 per cent of adults who received vitamin D and 25 per cent of those who received placebo, a 15 per cent relative reduction in risk.
The study, published in the journal Annals of Internal Medicine, extrapolated the findings to more than 374 million adults worldwide with prediabetes.
The research suggests that inexpensive vitamin D supplementation could delay the development of diabetes in more than 10 million people.
In an accompanying editorial, authors from University College Dublin and Food Safety Authority of Ireland, cautioned that previous research has demonstrated significant adverse impacts of high vitamin D intake.
They argue that professional societies promoting vitamin D therapy have an obligation to warn physicians about both required vitamin D intake and safe limits.
The researchers advise that a very-high-dose vitamin D therapy might prevent type 2 diabetes in some patients but may also cause harm.