How effective vitamin D supplements are may hinge on one’s weight

BOSTON — Vitamin D supplements are recommended to help boost health and protect our bodies from a number of ailments, but how much you weigh could play a key role in how effective they are. New research reveals that overweight and obese people don’t reap the same benefits of vitamin D because their bodies process it differently.

Researchers from Brigham and Women’s Hospital say those with a higher body mass index (BMI) metabolize the vital nutrient differently than their skinnier peers. The vitamin’s previously-discovered power to reduce the risk of cancer, heart disease, and stroke appear to be less effective among those with a higher BMI.

The essential nutrient helps the body absorb minerals such as calcium and magnesium. People can absorb it through sunlight as well as certain foods. Vitamin D also comes in supplements for those who are deficient. People who take the supplements had 30 to 40 percent reductions in cancer deaths and autoimmune diseases. However, those with a higher BMI taking the same amount had minimal results, according to researchers.

“Most studies like this focus on the total vitamin D blood level,” says senior author JoAnn Manson, MD, DrPH, chief of the Division of Preventive Medicine at the Brigham and principal investigator of VITAL, in a media release.

“The fact that we were able to look at this expanded profile of vitamin D metabolites and novel biomarkers gave us unique insights into vitamin D availability and activity, and whether vitamin D metabolism might be disrupted in some people but not in others.”

“This study sheds light on why we’re seeing 30-40 percent reductions in cancer deaths, autoimmune diseases, and other outcomes with vitamin D supplementation among those with lower BMIs but minimal benefit in those with higher BMIs, suggesting it may be possible to achieve benefits across the population with more personalized dosing of vitamin D,” Manson continues. “These nuances make it clear that there’s more to the vitamin D story.”

Obese people see a ‘blunted response to vitamin D’ supplements

The Brigham and Women’s Hospital team analyzed 16,515 people who took part in a previous 25,871-person trial on the benefits of vitamin D, known as VITAL. Scientists measured participants’ levels of vitamin D, and other biomarkers for the vitamin including metabolites, calcium, and parathyroid hormones which aid the body utilizing vitamin D.

They discovered that taking the vitamin supplements upped most of its associated biomarkers, regardless of people’s weight. However, the increase was significantly smaller among those with higher BMIs. Over the two-year study period, the reduced response became even more pronounced.

“The analysis of the original VITAL data found that vitamin D supplementation correlated with positive effects on several health outcomes, but only among people with a BMI under 25,” says first author Deirdre Tobias, ScD, an associate epidemiologist in Brigham’s Division of Preventive Medicine.

“There seems to be something different happening with vitamin D metabolism at higher body weights, and this study may help explain diminished outcomes of supplementation for individuals with an elevated BMI.”

“We observed striking differences after two years, indicating a blunted response to vitamin D supplementation with higher BMI,” Tobias concludes. “This may have implications clinically and potentially explain some of the observed differences in the effectiveness of vitamin D supplementation by obesity status.”

The team say their findings, published in the Journal of the American Medical Association (JAMA), are a call to action for people to continue exploring the benefits of vitamin D supplements.

South West News Service writer Pol Allingham contributed to this report.

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