High-Dose Vitamin D May Reduce Diabetes Risk for Some People, Study Finds
A widely available and inexpensive supplement may help lower the risk of developing Type 2 diabetes in certain people with prediabetes, according to new research published in JAMA Network Open.
Researchers found that a specific genetic variation in the vitamin D receptor gene may determine whether high-dose vitamin D supplementation is effective in preventing diabetes. The findings suggest that personalized treatment based on genetic testing could play a future role in diabetes prevention.
Genetic Differences Influence Benefits
The study analyzed data from the D2d clinical trial, which included more than 2,000 adults in the United States with prediabetes. Participants were randomly assigned to receive either 4,000 international units (IU) of vitamin D daily or a placebo for up to 3.5 years. For comparison, the recommended daily intake for most adults is 600 to 800 IU.
While the original trial found no significant overall reduction in diabetes risk, a follow-up genetic analysis revealed a more detailed picture. Researchers discovered that participants carrying the AC or CC variants of a gene known as ApaI experienced substantial benefits from vitamin D supplementation.
Over the course of the study, individuals with these genetic variants were 19 percent less likely to develop Type 2 diabetes than those who received a placebo. In contrast, participants with the AA variant—about 30 percent of those studied—showed no measurable benefit from supplementation.
“Diabetes has many serious complications that develop gradually over time,” said lead researcher Bess Dawson-Hughes. “If we can delay the onset of diabetes, we may reduce some of those complications or lessen their severity.”
How Vitamin D Affects Blood Sugar
Vitamin D plays an important role in several bodily functions. Once converted into its active form, it binds to vitamin D receptors found throughout the body. In the pancreas, vitamin D helps stimulate the release of insulin, the hormone responsible for regulating blood sugar levels.
Researchers believe that people carrying the AC and CC genetic variants respond more effectively to vitamin D, allowing them to gain greater protective benefits from supplementation.
Senior author Anastassios Pittas said the findings could pave the way for a more personalized approach to diabetes prevention.
“Vitamin D is attractive as a preventive tool because it is inexpensive, widely available, and easy for people to take,” he noted.
However, researchers stressed that additional studies are needed before high-dose vitamin D can be broadly recommended for diabetes prevention. Future screening may involve a simple genetic test to identify those most likely to benefit.
Checking Vitamin D Levels
According to registered dietitian Diana Cusa, the first step is to test blood levels of 25-hydroxyvitamin D.
“If your vitamin D levels are low, supplementation may be appropriate, along with reviewing your diet and sun exposure habits,” she said.
For general health, experts typically recommend 600 to 800 IU of vitamin D3 daily. Higher doses may be prescribed in cases of deficiency or in specific clinical prevention programs.
Current guidelines recommend:
1. 600 IU per day for adults up to age 70
2. 800 IU per day for adults over age 70
Excessive vitamin D intake can be harmful and has been linked to an increased risk of falls and fractures among older adults.
Natural Sources of Vitamin D
Sunlight remains one of the most effective natural sources of vitamin D. However, experts advise balancing sun exposure with appropriate skin protection, as excessive ultraviolet exposure increases the risk of skin cancer.
Unlike supplements, vitamin D obtained from sunlight does not cause toxicity. High-dose supplements, however, can lead to excessive vitamin D levels and should be taken under medical supervision.
Foods rich in vitamin D include:
a. Salmon
b. Tuna
c. Mackerel
d. Sardines
e. Rainbow trout
f. Beef liver
g. Egg yolks
h. Mushrooms
1. Cod liver oil
These foods also provide protein and healthy fats, which can help support stable blood glucose levels when consumed as part of a balanced diet.
The study highlights the growing role of genetics in preventive medicine and suggests that vitamin D supplementation may be most effective when tailored to an individual's genetic profile.