Vitamin D supplements may help reduce the risk of developing type 2 diabetes


ISLAMABAD: Individuals with prediabetes have blood sugar levels higher than what is considered healthy but not high enough to be diagnosed as type 2 diabetes.
It is a common condition — about 1 in 3 American adults have prediabetes, according to the U.S. Centers for Disease Control and Prevention. The good news is individuals with prediabetes can still prevent or delay the onset of type 2 diabetes.
A new systemic review and meta-analysis have found a higher vitamin D intake by individuals with prediabetes was associated with a 15% reduced risk of developing type 2 diabetes.
A paper about the review was published in the Annals of Internal Medicine.

2 different types of vitamin D
For the current review, the authors conducted a systemic review of the published literature looking for randomized, placebo-controlled diabetes prevention trials of vitamin D supplements in adults with prediabetes. That resulted in 3,835 citations from databases PubMed and Embase and 270 records from
Of these, 44 articles and all 270 records were screened. Three trials met the eligibility criteria. These were the 2019 study led by Pittas and the studies out of Norway and Japan.
The study out of Norway looked at 511 participants. The study out of Japan had 1,256 participants. The 2019 study led by Dr. Pittas had 2,423 participants.
The participants were not given the same vitamin D supplementation because of the different locations where the studies were conducted. Participants in the Norway and U.S. study received cholecalciferolTrusted Source, while the Japanese participants received eldecalcitolTrusted Source.
Of the combined 4,190 participants, 44% were women, 51% identified as white or European, 33% identified as Asian, and 15% identified as Black. The mean age of participants was 61. The mean Body Mass Index was 31, and the mean serum 25-hydroxyvitamin D level was 63 nanomoles per liter. The studies had a median follow-up of three years.
A consortium that included subject matter experts and the principal investigator from each study found eligible for the meta-analysis was formed.
Researchers obtained deidentified data sets from each study and gave the databases unified coding. The researchers then performed an IPD meta-analysisTrusted Source of the data.
Low frequency of adverse effects
When the authors of this review compiled individual participant data, they found vitamin D reduced the risk of developing diabetes by 12% in an unadjusted intention-to-treatTrusted Source analysis and 15% in an adjusted intention-to-treat analysis.
The rate of participants experiencing prespecified events like kidney stones, hypercalcemia, and hypercalciuriaTrusted Source was low. In the combined analysis, there were no statistically significant differences between vitamin D and placebo groups of adverse effects.
“We’re not super surprised because. [t]he [three separate] trials were very, very similar in the population they studied, in the outcome they measured and in the result was about the same,” Dr. Pittas told MNT.

“You just never know when you do a study what the final result will be, but we’re not super surprised [b]ecause we essentially increased the statistical power. So meta-analysis is almost like doing original trials, but all of a sudden adding two-thirds more of the population,” he added.
The authors of the review point out that the reduction of risk of developing diabetes is not as great as other diabetes prevention strategies.
Intensive lifestyle modification resulted in a 58% lower risk, and taking the drug metformin resulted in a 31% lower risk of developing diabetes in a 2002 studyTrusted Source.
Safety of vitamin D supplements
An editorial published in the same issue of Annals of Internal Medicine warns that the highest level of vitamin D intake “that carries no appreciable risk for adverse health effects, is set by all government agencies at 100 mcg (4,000 IU).”
The editorial pointed to two randomized clinical trials, including this one from 2018Trusted Source, where adult participants taking 250 micrograms (10,000 international units) of vitamin D daily for one to three years reported increased risk for adverse effects.
The authors go on to advise that “Very-high-dose vitamin D therapy might prevent type 2 diabetes in some patients but may also cause harm.”
That, Dr. Pittas told MNT, is a “reasonable point.”
However, he added a caveat: “[T]he one message I’d like to make that may not be conveyed by this editorial is that the benefit-risk ratio depends on the population and the condition you’re targeting.”
If an individual is at average risk for bone disease, Dr. Pittas provided as an example, the guidelines likely apply to you, “and it’s safe to no risk.”
“But if you are at risk for diabetes, then the guidelines are not very useful if you’re trying to prevent diabetes. And so, according to this meta-analysis, based on the trials, vitamin D at higher doses than typically recommended for the general population for supplement [to] decrease can reduce your risk of diabetes. In the meta-analysis, we did not find any risk.”
— Dr. Anastassios G. Pittas
More research on vitamin D needed
Dr. Elena Zamora, assistant professor of medicine with McGovern Medical School at UTHealth Houston, pointed out that four in ten adults are believed to be vitamin D deficient.
“The literature in the past has not reached a consensus regarding vitamin D and the correlation of chronic disease, so I appreciated that scholarly activity and meta-analysis has been devoted to this topic. And I think that it’s important that we continue this area of research given that there are vitamin D receptors in our muscle, heart and brain and immune system,” she told MNT.
Dr. Zamora cautioned, however, that the majority of dietary supplements are not regulated.
“We’ve heard about contamination with microbes, metals that may be found in supplements. And so, as more and more correlations with vitamin D levels and chronic comorbid conditions. [are reported], I think we also need to parallel the regulation of supplements,” she said.
Dr. Pittas plans to undertake research in the future looking at what dose of vitamin D provides the best reduction of risk of developing type 2 diabetes in adults with prediabetes with few adverse effects.