Weight loss among women helps raise blood vitamin D levels

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

“Since vitamin D is generally lower in [people] with obesity, it is possible that low vitamin D could account, in part, for the link between obesity and [such] diseases [as] cancer, heart disease and diabetes,” said Caitlin Mason, lead author of the paper, published online May 25 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.”

According to the National Institutes of Health, vitamin D helps promote calcium absorption and is needed for bone growth and bone healing. Along with calcium, vitamin D also helps protect older adults from osteoporosis. The nutrient influences cell growth and neuromuscular and immune function, and also reduces inflammation. Many gene-encoding proteins that regulate cell proliferation, differentiation and apoptosis (programmed cell death) are modulated in part by the vitamin.

The yearlong study involved 439 overweight to obese, sedentary, postmenopausal Seattle-area women, ages 50 years to 75 years, who randomly were assigned to 1-of-4 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 lbs. 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,” said Anne McTiernan, 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).

The optimal circulating range of vitamin D is thought to be between 20 ng/mL and 50 ng/mL, according to a recent data review conducted by the Institute of Medicine, which found that blood levels under 20 ng/mL are inadequate for bone health and levels higher than 50 ng/mL are associated with potential adverse effects, such as an increased risk of developing kidney stones.

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