Vitamin D Linked to Modest Decrease in Weight Gain

Additional support for the role of vitamin D in weight regulation was published online this week.

The researchers found that adequate vitamin D levels were associated with less weight gain among women aged 65 years and older during a 4.5-year period, although they failed to find an association for weight loss and vitamin D.

Erin S. LeBlanc, MD, MPH, an epidemiologist and endocrinologist at the Center for Health Research, Kaiser Permanente Northwest, Portland, Oregon, and colleagues tested hydroxylvitamin D status (25[OH]D) and tracked weight among participants who were mostly non-Hispanic white (>99%) and aged 65 years or older were recruited from a long-term Study of Osteoporotic Fractures from 1986 to 1994.

Using a 25(OH)D level of 30 ng/mL or higher as the marker for adequate vitamin D levels, the investigators found an association between lower weight at baseline and adequate vitamin D levels (141.6 pounds for women with 25 (OH)D levels ≥ 30 ng/mL; 148.6 for women with 25 (OH)D levels < 30 ng/mL; P < .001) among 4659 women in a baseline study. The 30 ng/mL cutoff was chosen because of previous research suggesting calcium absorption is most efficient above this level. The Endocrine Society sets its guidelines for vitamin D at this level.

Researchers also found an association between vitamin D levels at baseline and reduced weight gain 4.5 years later in these women. Further, they uncovered an association between long-term vitamin D levels and weight gain among a subset of 1054 women who had 25(OH)D tested both at year 6 and year 10 of the long-term study.

Women with adequate vitamin D at baseline who gained weight gained less weight than those with lower vitamin D, the investigators found. Among women who had 25(OH)D tested only at baseline, those with a vitamin D level of 30 ng/mL or higher gained less weight (16.45 pounds; standard error [SE], 1.17 pounds) than women with 25(OH)D levels lower than 30 ng/mL (18.47 pounds; SE, 0.87 pounds; P = .04). The figures are adjusted for baseline weight, age, season, follow-up years, clinic, and smoking status. There was no association in the weight loss group (P = 0.79) or in the stable weight group (P = .64).

Among the subset of 1054 women in the longitudinal trial, there was also an association between vitamin D levels and amount of weight gained. Women who maintained adequate vitamin D during the 4.5 years between tests, or who increased 25(OH)D levels to 30 ng/mL or more, gained 14.81 pounds (SE, 1.31 pounds). Women whose 25(OH)D levels were consistently lower than 30 ng/mL, or whose levels fell below 30 ng/mL, gained an average of 16.34 pounds (SE, 1.08 pounds; P = .04). The figures are adjusted for baseline weight, age, season, follow-up years, history of diabetes, and smoking status. The association failed to reach significance in the weight loss group (P = .06) in figures adjusted for baseline weight, age, season, follow-up years, and functional status.

The researchers conducted another analysis using 25(OH)D levels of 20 ng/mL as the cutoff and found no association between vitamin D at this cutoff level and weight change.

"Our results extend previous cross-sectional data showing that low 25(OH)D levels are associated with increased body fat and obesity," the authors write. "Some have proposed that increased body fat is associated with lower 25(OH)D levels because 25(OH)D accumulates in fat or because of lifestyle differences between obese and nonobese populations. However, our longitudinal data in older women gaining weight are consistent with the hypothesis that low 25(OH)D levels could actually predispose to fat accumulation."

The authors note that vitamin D supplements are known to reduce fat mass in animals, and that in vitro 25(OH)D directly regulates differentiation and transcription in adipocytes. In its active form, 1,25 dihydroxyvitamin D3 can induce cell death in adipocytes. When 25(OH)D is in short supply, secretions of parathyroid hormone are increased, which increases lipogenesis and decreases lipolysis.

Because the study was conducted in postmenopausal white women, it may not be generalizable to other ethnic groups, age groups, or men, nor may it apply to those with poorer health.

J Womens Health. Published online June 25, 2012.