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-hydroxyvitamin D [25(OH)D] concentrations.

Overweight and obese postmenopausal women (n = 439) were randomly assigned to 1 of 4 groups: 1) diet modification (n = 118), 2) exercise (n = 117), 3) diet + exercise (n = 117), or 4) control (n = 87). The diet intervention was a group-based reduced-calorie program with a 10% weight-loss goal. The exercise intervention consisted of 45 min of moderate-to-vigorous intensity aerobic activity daily for 5 d/wk. Serum 25(OH)D concentrations were measured by using a competitive chemiluminescent immunoassay at baseline and 12 mo.

No significant change in serum 25(OH)D was found between the intervention and control groups. Women who lost <5%, 5-9.9%, 10-14.9%, or ≥15% of baseline weight had mean increases in 25(OH)D of 2.1, 2.7, 3.3, and 7.7 ng/mL, respectively (P for trend = 0.002). Baseline vitamin D status did not modify the effect of the interventions on weight loss or body-composition changes at the 12-mo 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. This trial is registered at as NCT00470119.