Researchers are reconsidering the role of vitamin D in preventing type 2 diabetes, after a recent study showed that its effect may be largely dependent on genetics.
The study indicates that vitamin D may help reduce the risk of disease development, but this effect is not seen in everyone, and is linked to specific genetic variations in the vitamin D receptor gene.
The researchers explained that people with prediabetes who carry certain variations in the vitamin D receptor gene had a 19% lower risk of developing diabetes when they took a high daily dose of vitamin D.
The study relied on data from the multicenter D2d clinical trial, which included more than 2,000 American adults with prediabetes. The trial compared taking 4,000 IU of vitamin D daily with a placebo, aiming to assess the vitamin's effect in reducing the risk of developing diabetes.
However, the preliminary results did not show an overall decrease in the risk of infection among all participants.
Bess Dawson-Hughes, the study's lead researcher and senior scientist at the Jan Mayer Center for Human Nutrition Research at Tufts University, explained that these findings raised a question about why some people benefit from vitamin D while others do not.
In a previous analysis within the study, it was found that a blood level of 25-hydroxyvitamin D between 40 and 50 nanograms/ml or higher is associated with a reduced risk of developing diabetes.
Vitamin D is converted inside the body into its active form, and then binds to its receptors found in multiple cells, including pancreatic cells responsible for insulin secretion, which supports the hypothesis of its role in regulating blood sugar.
Based on this, the researchers investigated whether genetic variations in the vitamin D receptor explain the variability in response among individuals. The analysis included genetic data from 2,098 participants in the D2d trial, who were categorized according to their response to supplementation, and then compared based on three common variations in the receptor gene.
The results showed that carriers of the AA genotype of the vitamin D receptor gene ApaI, who were about 30% of the participants, did not show a clear response to vitamin D treatment compared to the placebo.
In contrast, individuals with AC and CC genotypes showed a significant reduction in the risk of developing diabetes when receiving the high daily dose.
Anastasios Pittas, a professor of medicine at Tufts University and one of the study's senior authors, said these findings represent an important step toward developing preventative strategies aimed at people most at risk.
He noted that vitamin D may be a promising option given its low cost and easy availability.
At the same time, the researchers stressed that high doses of vitamin D should not be taken without medical supervision, as excessive intake may lead to harmful effects, including an increased risk of falls and fractures in the elderly.
Current health guidelines recommend a daily intake of 600 IU for adults up to age 70, and 800 IU for those over 70. The study underscores the need for further research to identify the groups that might actually benefit from higher doses.
The study was published in the journal JAMA Network Open.
