Health Day Reporter
TUESDAY, Jan. 24, 2023 (HealthDay News) — Vitamin D is widely touted for improving health, but if you’re overweight, you may not benefit from it.
In a new study, researchers found that among people with a lower body mass index (BMI) who took vitamin D supplements, the incidence of cancer, cancer death, and autoimmune disease was 30% to 40% lower, but For those with a higher BMI, the benefit was small.
“Obese patients had lower responses despite taking the same amount of supplementation,” said lead researcher Deirdre Tobias, an assistant professor in the Department of Nutrition at the Harvard School of Public Health in Boston.
The study authors noted that the cutoff was a BMI of less than 25, which is considered a healthy weight.
It’s not clear why being overweight or obese affects levels of the so-called “sunshine vitamin,” but according to the U.S. Centers for Disease Control and Prevention.
“It’s not clear whether this is due to their weight itself, or some other factor related to the individual’s weight. It could be due to obesity itself. Lower body weight may lead to higher internal doses of vitamin D,” Tobias said. Obesity is excess fat tissue in the body.
The next step in the research, she noted, is to try to tease out what body weight actually affects vitamin D metabolism.
Tobias also said it was unclear whether overweight and obese people could offset the lower effects of vitamin D supplements by taking higher doses.
“It’s not one of those vitamins that you can take in unlimited amounts. If you take too much, you’re going to pass it out primarily in your urine,” she said. “Therefore, taking higher doses just to be on the safe side is not implied or recommended by this study.”
For the study, Tobias and her colleagues used data from the Vitamin D and Omega-3 Trial (VITAL), which randomly assigned nearly 26,000 older adults to receive vitamin D supplements or a placebo. Although the trial showed little benefit in preventing cancer, heart attack or stroke from taking vitamin D supplements, there appeared to be a correlation between body weight and the risk of developing cancer, cancer death and autoimmune disease.
The researchers decided to dig deeper into the data. They looked at about 16,500 participants who provided blood samples at the beginning of the trial and nearly 3,000 participants who provided follow-up blood samples two years later.
The researchers found that signs of vitamin D metabolism were seen in all participants regardless of body weight, but far fewer were overweight or obese.
“Vitamin D has been shown to reduce the risk of osteoporosis and other chronic diseases,” said Emma Lane, director of nutrition at the University of Georgia and national spokesperson for the College of Nutrition and Dietetics.
Lane noted that scientists have come up with some ways in which vitamin D supplements might be less effective in larger people. “Because vitamin D is a fat-soluble vitamin, people with higher levels of adipose tissue may store more vitamin D in these tissues and thus have less vitamin D detected in the blood. Another hypothesis is that adipose tissue suppresses enzymes and receptors that are responsible for how vitamin D works in the body,” she said.
Laing does not recommend taking vitamin D supplements without first consulting your doctor because of the possible side effects of the supplements. “If you take more than recommended doses, take a variety of supplements, or take supplements that interact negatively with medications, adverse events ranging from less serious to life-threatening can occur,” she said.
Still, Laing notes that supplements can be helpful in some cases.
Taking a vitamin D supplement may be appropriate if you’re unable to obtain the necessary amounts through your diet, or if you limit sun exposure due to climate, skin tone, or use of sunscreen, she says.
“Supplements may be needed if a person removes food groups from their eating pattern, is diagnosed with a vitamin or mineral deficiency, or takes medications that affect appetite or interfere with nutrient digestion and absorption,” Lane said. In these cases, she suggests, it may be necessary to obtain vitamins and minerals from supplements.
Additionally, when food choices are severely restricted due to food allergies or intolerances, a strict diet, or a medical condition such as celiac disease, supplements are often recommended to prevent vitamin and mineral deficiencies, Laing explains.
Also, people who have had weight loss surgery may need supplements. “Competitive athletes and the military may also need supplements if they serve, if their physical performance demands make it difficult to meet their nutritional needs from food alone,” Lane said.
The report was published online January 17 at JAMA Network is open.
For more information on vitamin D, go to the US National Library of Medicine.
Sources: Deirdre Tobias, ScD, Assistant Professor, Department of Nutrition, Harvard School of Public Health, Boston; Emma Laing, PhD, RDN, Director of Nutrition, University of Georgia, Athens, National Speaker for the School of Nutrition and Dietetics; JAMA Network OpenOnline, January 17, 2023