Increased Circulating Vitamin D Levels Associated with Weight Loss

Caitlin Mason, from the Fred Hutchinson Cancer Research Center in Seattle, Washington writes, "Low concentrations of circulating vitamin D are common with obesity and may represent a potential mechanism explaining the elevated risk of certain cancers and cardiovascular outcomes observed in individuals who are overweight or obese. "The objective of this study was to investigate the effects of 12 mo of weight loss through caloric restriction, exercise intervention, or both on serum [25(OH)D] concentrations."

In this study, 438 overweight and obese postmenopausal women were randomly assigned to dietary modification (n = 118), an exercise intervention (n = 117), diet plus exercise (n = 117), or to a control group (n = 87). Women receiving the dietary intervention had a 10% weight loss goal using a group-based reduced-calorie program, and those receiving the exercise intervention underwent 45 minutes of moderate to vigorous intensity aerobic activity daily for 5 days/week. Using an immunoassay, the investigators measured serum 25(OH)D concentrations at baseline and at 12 months.

The intervention and control groups did not differ significantly in serum 25(OH)D concentrations. Women who lost less than 5%, 5% to 9.9%, 10% to 14.9%, or 15% or more of baseline weight had mean increases in 25(OH)D levels of 2.1, 2.7, 3.3, and 7.7 ng/mL, respectively (P for trend = .002). Vitamin D status at baseline was not associated with any modulation of the interventions' effects on weight loss or changes in body composition at 12-month follow-up.

"A greater degree of weight loss, achieved through either a reduced-calorie diet or increased exercise, is associated with increased circulating 25(OH)D concentrations," the study authors write.

Limitations of this study include inability to determine whether vitamin D status influences successful weight loss, low mean concentrations of 25(OH)D overall, and inadequate range of serum concentrations to detect an effect. In addition, sun exposure was not assessed in this trial.

Although greater adiposity is associated with lower concentrations of circulating vitamin D, our findings suggest that lifestyle-based weight loss of 5% to 10% body weight is associated with a modest increase in serum 25(OH)D.  However, baseline vitamin D status had little effect on the achievement of weight loss in a sample of overweight and obese postmenopausal women. Ongoing research to better understand the role of vitamin D in pathways influencing energy balance may lead to a clearer understanding of optimal vitamin D concentrations for promoting health in human populations.

Am J Clin Nutr. Published online May 25, 2011