Key Takeaways
Vitamin D supplements, combined with diet and exercise, may help some people with prediabetes return to normal blood sugar levels.Vitamin D can support pancreatic beta-cells and help with insulin secretion.A higher-dose vitamin D supplement may benefit people with prediabetes.
Vitamin D is best known for supporting bone health, but growing evidence suggests it may also play a role in blood sugar control, especially in people with prediabetes.
A new analysis of clinical trials found that vitamin D supplements may help some people with prediabetes return to normal blood sugar levels when used alongside regular exercise and a balanced diet.
How Might Vitamin D Help With Blood Sugar Control?
In the analysis, vitamin D supplementation increased the likelihood of returning from prediabetes to normal blood sugar levels by 27% compared with placebo.
The primary effect of vitamin D is to improve the secretion of insulin by beta-cells in the pancreas, according to Anastassios Pittas, MD, senior author of the study and codirector of the Diabetes Clinic at Tufts Medicine.
“If you don’t have prediabetes, the supplementation will not help you in terms of diabetes,” Pittas told Verywell.
Vitamin D may also help reduce inflammation, which has been linked to insulin resistance and impaired glucose uptake.
Does High-Dose Vitamin D Help With Prediabetes?
Across the clinical trials, the average daily dose was about 4,300 IU—well above the current recommendations of 600 IU for adults ages 19 to 70 and 800 IU for those 71 and older.
In 2024, the Endocrine Society released guidelines recommending that high-risk adults with prediabetes take vitamin D doses above the recommended daily allowance to reduce the risk of progression to diabetes.
While the guidelines did not specify a daily dose, the estimated average was approximately 3,500 IU per day based on the clinical trials that informed the recommendation.
“Vitamin D is so safe that if anyone is worried they don’t get enough from their diet or the sun, they should supplement. But avoid megadoses above 5,000 IU per day, which have not been tested for safety long term,” said JoAnn Manson, MD, a professor of medicine at Harvard Medical School.
Very few foods naturally contain vitamin D. However, many foods are fortified with it, including dairy and plant-based milks, breakfast cereals, and orange juice. Fatty fish such as trout, salmon, and tuna are among the best natural sources. Beef liver, egg yolks, and cheese have smaller amounts of vitamin D.
Rozalina McCoy, MD, associate division chief for clinical research at the Division of Endocrinology, Diabetes, and Nutrition at the University of Maryland School of Medicine, said she worries that high-dose vitamin D supplements could lead to hypercalcemia, a condition in which too much calcium accumulates in the blood. This can weaken bones, create kidney stones, and affect the heart and brain.
If you have prediabetes, it’s best to consult with a doctor before you start any vitamin D supplement.
“I think it is an individual decision and ultimately there are more effective ways to prevent progression of prediabetes to diabetes with [a] focus on lifestyle optimization,” McCoy said.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Kretschmer PM, Balk EM, Pittas AG. Effect of vitamin D on regression to normal glucose regulation in adults with prediabetes. J Endocr Soc. 2025;9(5):bvaf042. doi:10.1210/jendso/bvaf042
Argano C, Mirarchi L, Amodeo S, Orlando V, Torres A, Corrao S. The role of vitamin D and its molecular bases in insulin resistance, diabetes, metabolic syndrome, and cardiovascular disease: state of the art. Int J Mol Sci. 2023;24(20):15485. doi:10.3390/ijms242015485
National Institutes of Health. Vitamin D fact sheet for health professionals.
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