More than 374 million adults worldwide have prediabetes. The findings suggest that a low-cost vitamin D supplement could delay the development of diabetes in more than 10 million people.


The risk reduction was 15%, with the conclusion adjusted for age, gender, body mass index and other factors. This is shown by data from a meta-analysis of three randomized clinical trials. 


3.3% of participants had an absolute reduction in risk over 3 years. The trend persisted in a secondary analysis that excluded patients who stopped taking experimental antidiabetic drug therapy, developed diabetes, or started weight loss medication.


It turns out that patients who took vitamin D supplements were 30% more likely to return to normal glucose levels.


In all three studies, participants took 20,000 IU (500 mcg) of cholecalciferol weekly, or 4,000 IU (100 mcg) daily. All were compared with a matched placebo.


Dr Malachi McKenna of University College Dublin and Dr Mary Flynn of the Irish Food Safety Authority point out that on their own, all three trials found an identical reduction in the risk of diabetes associated with vitamin D supplementation, but the independent original studies were simply "underpowered" to detect the effect on diabetes progression.


Although none of the meta-analyses reported an increased risk of kidney stones, hypercalcemia or hypercalciuria, or any other risk, the researchers explained that there are reasonable and acceptable limits of vitamin D intake that should be consulted with the appropriate attending physician.


The total number of participants in the three studies was 4,190, 2,097 receiving vitamin D and 2,093 receiving placebo. The average age is 61 years, 44% are women. Mean BMI was 29.5 and HbA1c was 5.9 at baseline.


During a median follow-up of 3 years, there were 475 new cases of diabetes diagnosed among those taking vitamin D versus 524 in the placebo groups. The reduction in risk was much more pronounced for those who maintained higher serum 25-hydroxyvitamin D levels.


Compared with those who maintained lower serum levels during follow-up—falling in the range of 50 to 74 nmol/L (20 to 29 ng/mL)—those who maintained levels of at least 125 nmol/L (≥50 ng /mL) had a 76% reduced risk of progression to diabetes (HR 0.24, 95% CI 0.16-0.36). This translates to a 3-year absolute risk reduction of 18.1% (95% CI 11.7-24.6%).



Anastassios G. Pittas, MD, MS. Vitamin D and Risk for Type 2 Diabetes in People With Prediabetes. Annals of Internal Medicine -