Background/Objectives:Although weight loss has been associated with changes in circulating 25-hydroxyVitamin D (25(OH)D) levels, the quantification of the increase in 25(OH)D levels as a function of adipose tissue volume loss precisely assessed by imaging has not been reported before. The objective of this substudy was to describe the effects of a 1-year lifestyle intervention on plasma 25(OH)D levels. The relationships between changes in 25(OH)D levels and changes in adiposity volume (total and by adipose tissue compartment) were studied.Subjects/Methods:This intervention study was performed between 2004 and 2006 and participants were recruited from the general community. Sedentary, abdominally obese and dyslipidemic men (n=103) were involved in a 1-year lifestyle modification program. Subjects were individually counseled by a kinesiologist and a nutritionist once every 2 weeks during the first 4 months with subsequent monthly visits in order to elicit a 500-kcal daily energy deficit and to increase physical activity/exercise habits. Body weight, body composition and fat distribution were assessed by dual-energy X-ray absorptiometry and computed tomography, whereas the 25(OH)D levels were measured with an automated assay.Results:The 1-year intervention resulted in a 26% increase in circulating 25(OH)D (from 48±2 nmol l -1 or 19±0.8 ng ml -1 (±s.e.m.) to 58±2 nmol l -1 or 23±0.8 ng ml -1, P<0.0001) along with a 26% decrease in visceral adiposity volume (from 1947±458 to 1459±532 cm 3). One-year increases in 25(OH)D levels correlated inversely with changes in all adiposity indices, especially Δvisceral (r=-0.36, P<0.0005) and Δtotal abdominal (r=-0.37, P<0.0005) adipose tissue volumes.Conclusions:These results indicate that there is a linear increase in circulating 25(OH)D levels as a function of adiposity volume loss, and therefore suggest a role of adiposity reduction in the management of obesity-associated Vitamin D insufficiency.