New Research Find That Vitamin D Supplementation Doesn’t Lower Type 2 Diabetes


There are a number of former observational studies that suggest how taking vitamin D supplements reduce the risk of developing of type 2 diabetes, but a new major study shares that this isn’t the case.

In fact, a research group studied how higher-than-normal levels of vitamin D can actually affect the onset of the disease in adults that have satisfactory levels of vitamin D and were at risk for type 2 diabetes.

The vitamin D and type 2 diabetes study, which has been dubbed D2d, was published in the June 2019 copy of The New England Journal of Medicine (NEJM). The authors even presented their findings at the American Diabetes Association’s (ADA) 79th Scientific Sessions at the Moscone Convention Center in San Francisco.

Myrlene A. Staten, MD, who happens to be the D2d project scientist at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), which funded the study, explained, “You can trust that, for an American population, taking vitamin D is not going to reduce the risk by 25 percent or more.”

The study, which happens to be the largest ever clinical trial that was created to explore the effects of vitamin D supplementation on diabetes onset, focused on the big numbers of people that were at risk for type 2 diabetes. According to the study authors, over 84 million Americans, which is around 1 in 3 people above the age of 20 – are considered high risk for developing diabetes. In more recent years, experts have also explored a variety of approaches to delay or reduce the onset of diabetes.

Notably, the researchers decided to conduct the D2d study due to former observational studies, one of which was published in the December 2014 journal of Diabetes Care. This particular study suggested that having a low vitamin D level tends to be associated with a range of health issues, including diabetes. But according to the authors, the Recommended Daily Allowance (RDA) for vitamin D is 600 international units (IU) per day for adults between 18 to 70 years of age, and 800 IU a day for adults aged 71 and above. But the nutrient, which is generated within the body when individuals are exposed to sunlight, many people don’t get enough sun exposure to reach these levels, therefore they are usually deficient.

Dr. Staten says, “Observational studies are important for generating hypotheses and ideas of what might be. But there are so many factors that can affect observational studies. There is no way to know if changing the levels — giving them a pill of vitamin D — is going to make a difference. You have to confirm observational studies with controlled trials.”

How D2d Was a Different Study on Vitamin D and Type 2 Diabetes

The research group designed D2d to take a deeper look into the usefulness of vitamin D supplementation through the gold standard research format, which was the randomized clinical trial. It launched the study back in 2013, having enrolled 2,423 participants that had a risk of diabetes. This was based on the individuals meeting at least two out of three glycemic criteria. They also randomly assigned participants to take a 4,000 IU vitamin D pill daily or a placebo pill. From there, the researchers followed the participants for the development of diabetes between two to five years, having them undergo blood tests every six months. The researchers also told the participants to avoid taking other diabetes-specific or weight loss medication.

While the research group specifically designed the study to ‘detect a reduction in the risk of developing diabetes of 25 percent or more with vitamin D,’ they observed no such reduction in the patients. Although there were less people that were taking the vitamin D supplement as compared to the placebo group that developed diabetes – 24.2 compared with 26.7 percent – it wasn’t a large enough difference to be considered statistically significant.

According to Deborah J. Wexler, MD, who did a commentary on the study that was published in June 2019 in The New England Journal of Medicine, “The Dd2 trial was a well-conducted randomized, controlled trial that addresses an important hypothesis in diabetes prevention. “ Although Dr. Wexler was not involved in the study, she is an associate professor of Medicine at Harvard Medical School and co-clinical director of the Massachusetts General Hospital Diabetes Center, located in Boston.

She adds, “Any benefit of vitamin D for diabetes prevention, if present, is modest and clearly does not pertain to a vitamin D-sufficient population.”

The authors explain that in this study, the ability of vitamin D supplementation to prevent type 2 diabetes could be because of the high number of people in the trial that already had sufficient vitamin D levels.

Dr. Staten said, “If you’re vitamin D deficient, you should take vitamin D to get up to sufficient levels. Our trial hints that it may prevent diabetes if you’re deficient. But we can’t be firm in that result. That finding is a very soft finding.”

Staten also reports that the data implies how vitamin D supplementation may confer a lower level of risk, like a 10 percent reduction. She continues, “The trial was designed to be able to detect a 25 percent reduction,” explaining that there is also a change that vitamin D reduces diabetes risk by a smaller percentage, except the team didn’t test for that.

But they also shared that the results of the D2d study weren’t completely surprising. A review that was published in the October 2014 copy of the Journal Endocrinology & Metabolism also looked at studies that compared the effect of taking vitamin D supplements with a non-vitamin D supplement or placebo in adults that had normal glucose levels, prediabetes, or type 2 diabetes, finding no effect from taking the vitamin D supplements on either glucose levels or diabetes prevention.

Important Facts to Know on How to Help Prevent Type 2 Diabetes

As explained by Dr. Wexler in the NEJM commentary, for now, people that are at a higher risk for diabetes should practice lifestyle modifications, like eating a healthy diet and exercising regularly in order to help lessen their risk. The National Institute of Diabetes and Digestive and Kidney Diseases shares that a healthy diet is described as one that’s high in fresh, whole foods rich in nutrients, while being low in processed and packaged foods that tend to be high in trans or saturated fat, sodium, and added sugars. When it comes to exercise, the Department of Health and Human Services recommend doing a mix of cardiovascular exercise with strength training, which is equal to around two hours and 30 minutes a week.

The Centers for Disease Control and Prevention (CDC) also notes that their Diabetes Prevention Program is one of the highest and most effective public-private partnerships that’s aimed at helping individuals at risk for type 2 diabetes by helping them avoid developing getting the disease through simple methods such as diet and exercise.

Dr. Wexler adds, “In the Diabetes Prevention Program, the risk of progression to type 2 diabetes over a period of 2.8 years was lower by 58 percent with a lifestyle intervention than with placebo, and lower by 31 percent with metformin than with placebo, with similar-sized treatment groups as in the D2d trial.” 

Despite the result of the study, the D2d researchers will continue to look at the role of vitamin D on the body, and how it uses it and creates insulin, as well as how it impacts other conditions like cancer and heart disease.

Dr. Staten also says, “There are other disciplines that are looking at those types of outcomes. Maybe we didn’t have a major effect, but who knows for them?”