Benefits of Vitamin D May Depend on Body Weight

Vitamin D is a crucial part of our health, associated with guiding our bodies to absorb and keep calcium and phosphorus. However, a new study suggests that our body weight may affect how we benefit from vitamin D.

The study by the Brigham and Women’s Hospital, published in JAMA Network Open, looked at whether body mass index (BMI) plays a role in vitamin D metabolization. The study is referred to as the VITamin D and OmegA-3 TriaL (VITAL) trial, a comprehensive clinical trial by Brigham.

It was created to further study relationships between vitamin D supplement and its correlation with cancer risk reduction, heart disease, and stroke.

"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,” said co-author Deirdre K. Tobias, ScD, also 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."

One of many functions of vitamin D is to aid the body's absorptions of minerals, including calcium and magnesium. Vitamin D we need is sometimes provided to us by direct sunlight, most vitamin D deficiencies require extra supplementation.

The initial VITAL experiment was spurred by evidence that vitamin D may be involved in the occurrence and development of cancer and cardiovascular disease, per various studies and research.

What did the research find?

In the randomized, double-blind, placebo-controlled VITAL experiment, 25,871 Americans participated, including men over 50 and women over 55. At the time of enrollment, every participant was healthy and free of both cancer and cardiovascular disease.

Despite minimal effect of vitamin D supplementation for preventing cancer, heart attacks, or stroke in the general population, there was a significant association between BMI and cancer incidence, cancer mortality, and the occurrence of autoimmune diseases. Similar outcomes for type 2 diabetes are suggested by other research.

Data from 16,515 study participants who submitted blood samples at baseline and 2,742 who provided blood samples for follow-up after two years were evaluated by the researchers.

They then calculated the total vitamin D, along with others including metabolites, calcium, and parathyroid hormone, which all guide our bodies to effectively use vitamin D.

"Most studies like this focus on the total vitamin D blood level,” said senior author JoAnn E. Manson, MD, DrPH, chief of the Division of Preventive Medicine at the Brigham and principal investigator of VITAL."

The VITAL study established that vitamin D supplementation heightened ultimately most of the biomarkers related with vitamin D metabolism, despite the weight. It did, however, show that the heightened results were noticeably smaller in those with higher BMI.

"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."

The study gathered that the VITAL findings should inspire more study into the possible advantages of vitamin D supplementation in restraining cancer and other complications, as well as encouraging scientists to take BMI into account when evaluating the supplement's potential health impacts.

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

"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,” continued Manson. “These nuances make it clear that there’s more to the vitamin D story."

What can vitamin D deficiency cause?

Vitamin D deficiency is common among the nation, with around 1 billion individuals suffering from it worldwide and about 50 percent having vitamin D insufficiency. In the United States, around 35 percent of adults deal with vitamin D deficiency.

Even infants can have vitamin D deficiency, and can affect everyone despite their age. It is known to be more common in individuals with larger skin melanin content, and those who tend to wear more covering clothing, as it blocks sunlight from touching the skin.

When vitamin D deficiency occurs, many physical symptoms can arrive, including fatigue, pain in the bones, mental health complications, such as depression, muscle cramps, or even joint deformities. It is also possible to have no physical signs despite vitamin D deficiency.

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