The healthy effects of vitamin D on our body do not seem to be the same for everyone. According to a team of researchers at Brigham and Women’s Hospital, vitamin D appears to be metabolized differently in people with a high body mass index (BMI).
The study, which appears in “JAMA Network Open,” is a new analysis of data from the VITAL triala large clinical trial that investigated whether taking marine-based omega-3 or vitamin D supplements could reduce the risk of developing cancer, heart disease or stroke.
“Analysis of the original VITAL data found that vitamin D supplementation was correlated with positive effects on several health outcomes, but only among people with a IMC inferior a 25», says Deirdre K. Tobias. “It appears that something different occurs with vitamin D metabolism at higher body weight, and this study may help explain the decreased results of supplementation in individuals with a high BMI.”
Vitamin D is an essential nutrient that is involved in many biological processes, especially in the absorption of minerals such as calcium and magnesium. Although some of the vitamin D we need is produced in the body from Sun light, vitamin D deficiencies are often treated with supplements. Laboratory studies, epidemiological research, and clinical research have also suggested that vitamin D may play a role in the incidence and progression of cancer and cardiovascular disease, and it was this evidence that prompted the original VITAL trial.
The VITAL trial was a randomized, double-blind, placebo-controlled trial in 25,871 American participants, among which there were men older than 50 years and women older than 55 years. All participants were free of cancer and cardiovascular disease at the time of enrollment. Although the trial found little benefit of vitamin D supplementation in preventing cancer, myocardial infarction or stroke in the overall cohort, a statistical correlation was observed between BMI and cancer incidence, cancer mortality, and incidence of autoimmune diseases. Other studies suggest similar results for type 2 diabetes.
The new study aimed to investigate this correlation. The researchers analyzed data from 16,515 original trial participants who provided blood samples at baseline (prior to random assignment to vitamin D), as well as 2,742 with a follow-up blood sample taken after two years. The researchers measured levels of total and free vitamin D, as well as many other novel vitamin D biomarkers, including its metabolites, calcium, and parathyroid hormone, which helps the body use vitamin D.
Other studies suggest similar results for type 2 diabetes.
“Most studies of this type focus on the total blood level of vitamin D,” says JoAnn E. Manson, the study’s lead author. “The fact that we were able to look at this expanded profile of vitamin D metabolites and new biomarkers gave us insight. unique perspective on availability and activity of vitamin Dand whether vitamin D metabolism might be altered in some people but not in others.”
The researchers found that vitamin D supplementation increased most biomarkers associated with vitamin D metabolism in people, regardless of weight. However, these increases were significantly less in people with high BMIs.
“We observed striking differences after two years, indicating a blunted response to vitamin D supplementation with higher BMI,” Tobias said. “This may have clinical implications and potentially explain some of the observed differences in the efficacy of vitamin D supplementation based on obesity status.”