Experts Say This Common Supplement May Lower Risk of Developing Type 2 Diabetes

In the latest study, researchers dove into genetic data from 2,098 people who participated in the trial. The researchers specifically compared the response to vitamin D supplement in people who had different common variations in the vitamin D receptor gene.

After crunching the data, the researchers discovered that with prediabetes who also had certain common variations in the vitamin D receptor gene had a 19% lower risk of developing type 2 diabetes when they took a high daily dose of vitamin D. (Those variations were AC or CC variations of the ApaI vitamin D receptor gene, if you want to get technical.)

While the findings don’t suggest that everyone with prediabetes should put themselves on a vitamin D supplement, the researchers note that it suggests genetic testing may be helpful in the future in identifying people with prediabetes who might benefit from higher doses of vitamin D.

But why vitamin D? Here’s the deal, according to experts.

Meet the experts: Anastassios Pittas, M.D.,the study’s senior author, a professor of medicine at Tufts University School of Medicine, and chief of endocrinology, diabetes, and metabolism at Tufts Medical Center; Scott Keatley, R.D., is co-owner of Keatley Medical Nutrition Therapy; Jessica Cording, R.D., is the author of The Little Book of Game-Changers; Keri Gans, R.D.N., is author of The Small Change Diet.

This isn’t the only study to suggest vitamin D may help prevent type 2 diabetes

One study that was published in the Journal of the Endocrine Society in 2025 analyzed data from 10 clinical trials that included nearly 4,500 people with prediabetes. The researchers found that 18.5% of the study participants who took vitamin D reached blood sugar levels that were normal, compared to the 14% of participants who took a placebo.

Another scientific analysis that was published in the Annals of Internal Medicinein 2023 analyzed data from three clinical trials on the impact of vitamin D supplementation on people with prediabetes. After three years of follow-up, the researchers found that that 22.7% of participants who took vitamin D developed type 2 diabetes, while 25% of those who took a placebo did the same.

So far, the differences between people who took vitamin D or a placebo haven’t been massive—but they have been noticeable. The latest findings suggest that diving a little deeper into genetics may drive that impact even more.

What’s behind this?

There are likely a few things happening here. “The vitamin D receptor is the ‘sensor’ that allows the body to use vitamin D,” says Anastassios Pittas, M.D.,the study’s senior author, a professor of medicine at Tufts University School of Medicine, and chief of endocrinology, diabetes, and metabolism at Tufts Medical Center. “In some individuals, this receptor works more efficiently, so higher vitamin D levels can better support processes such as insulin function, leading to better glucose control.”

But in others, the receptor doesn’t respond as well. “So, taking more vitamin D may not have the same benefit,” Dr. Pittas says.

Vitamin D doesn’t act on its own, points out Scott Keatley, R.D., co-owner of Keatley Medical Nutrition Therapy. It binds to the vitamin D receptor, which then sparks a reaction in tissues like the pancreas beta cells, he explains. “Those cells are responsible for insulin secretion,” Keatley says. (Insulin is what your body uses to escort blood sugar into your cells, where it’s used for energy.) “If the receptor is slightly different due to genetic variation, the same vitamin D level can produce a different biological response,” Keatley says.

How can you know if vitamin D will help you?

There’s no quick and easy way to know if you have these genetic variations, according to Keri Gans, R.D.N., author of The Small Change Diet. “Right now, most people would not know,” she says. “This is based on a specific genetic variation, and that is not routinely tested for in standard care.”

However, you may notice some clues, according to Jessica Cording, R.D., the author of The Little Book of Game-Changers.

Cording suggests knowing what your vitamin D status is at baseline. “Blood work is very important, and this is a really easy test,” she says. “That will give you some clues as to if you’re deficient and should supplement, along with how high of a dose.”

But follow-up blood work is especially crucial, per Cording. “That will help you see how your body responds to vitamin D and will give you clues to see whether you should continue or stop, or if you need a higher dose,” she says.

What is a ‘high dose’ of vitamin D?

It depends. “Traditionally, a ‘high’ dose has been defined as intake above 4,000 IU per day, which was set as the Tolerable Upper Intake Level by the Institute of Medicine in 2011,” Dr. Pittas says. “That said, thinking has evolved.”

Now, he says that healthcare providers imply think about what may be appropriate for each person, noting that this is often show in blood work. “In studies on type 2 diabetes prevention, greater benefit has been observed among individuals who achieve and maintain higher blood levels of 25-hydroxyvitamin D—around or above 40 ng/mL,” Dr. Pittas says. “Reaching these levels requires doses higher than 4,000 IU/day in some individuals.”

Do you need a vitamin D supplement?

If you have prediabetes, a vitamin D supplement is unlikely to be the way to avoid progressing to type 2 diabetes, whether you have this special genetic variant or not. “Diet and exercise are still the main drivers,” Keatley says. “When people with prediabetes improve diet quality, lose some weight, and move more, the reduction in diabetes risk is typically much larger and more consistent than what we see from any single nutrient.”

That doesn’t mean vitamin D is worthless, though. “Vitamin D, if it plays a role here, would likely be a smaller, supportive effect,” Keatley says. “Think of it as something that might fine-tune risk in certain people, not something that replaces the basics.”

Ultimately, if you have prediabetes and want to lower your risk of developing type 2 diabetes, it’s important to have a conversation with your healthcare provider about your treatment options.

Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing. Also, be careful about giving supplements to a child, unless recommended by their healthcare provider.