Body Weight Loss Boosts Vitamin D Levels in Obese Women

Overweight or obese women with less-than-optimal levels of vitamin D who lose more than 15% of their body weight experience significant increases in circulating levels of this fat-soluble nutrient, according to a new study by researchers at Fred Hutchinson Cancer Research Center.

“Since vitamin D is generally lower in persons with obesity, it is possible that low vitamin D could account, in part, for the link between obesity and diseases such as cancer, heart disease, and diabetes,” says Caitlin Mason, PhD, lead author of the paper published online in the American Journal of Clinical Nutrition.

“Determining whether weight loss helps change vitamin D status is important for understanding potential avenues for disease prevention,” says Mason, a postdoctoral research fellow in the Hutchinson Center’s Public Health Sciences Division.

The year-long study involved 439 overweight-to-obese, sedentary, postmenopausal, Seattle-area women, aged 50 to 75, who were randomly assigned to one of four groups: exercise only, diet only, exercise plus diet, and no intervention.

Those who lost 5% to 10% of their body weight—equivalent to approximately 10 to 20 lbs for most of the women in the study—through diet and/or exercise saw a relatively small increase in blood levels of vitamin D (about 2.7 ng/mL), whereas women who lost more than 15% of their weight experienced a nearly threefold increase in vitamin D (about 7.7 ng/mL), independent of dietary intake of the nutrient.

“We were surprised at the effect of weight loss greater than 15% on blood vitamin D levels,” says senior author Anne McTiernan, MD, PhD, director of the Hutchinson Center’s Prevention Center and principal investigator of the study. “It appears that the relationship between weight loss and blood vitamin D is not linear but goes up dramatically with more weight loss. While weight loss of 5% to 10% is generally recommended to improve risk factors such as blood pressure, cholesterol, and blood sugars, our findings suggest that more weight loss might be necessary to meaningfully raise blood vitamin D levels.”

About 70% of the participants had less-than-optimal levels of vitamin D when the study began; at baseline, the mean blood level of vitamin D among the study participants was 22.5 ng/mL. In addition, 12% of the women were at risk of vitamin D deficiency (blood levels of less than 12 ng/mL).

“It is always best to discuss supplementation with your doctor, because circulating levels can vary a lot depending on factors such as age, weight, where you live, and how much time you spend outdoors,” Mason says. Vitamin D levels tend to decrease as people age and are generally lower among those with dark skin.

It is thought that obese and overweight people have lower levels of vitamin D because the nutrient is stored in fat deposits. During weight loss, it is suspected that the vitamin D that is trapped in the fat tissue is released into the blood and available for use throughout the body.

Source: Fred Hutchinson Cancer Research Center