Adiposity, vitamin D requirements, and clinical implications for obesity-related metabolic abnormalities.

This review was conducted to clarify both the complex interrelationship between adiposity and vitamin D and the clinical implications of vitamin D status on metabolic abnormalities associated with obesity. Obesity increases the risk of vitamin D deficiency, a finding consistently reported across all ages and in different population groups. According to genetic studies, this is driven by the effect of higher adiposity, which causes a reduction in circulating concentrations of 25-hydroxyvitamin D [25(OH)D, used as an indicator of vitamin D status]. Conversely, higher concentrations of 25(OH)D do not appear to affect the risk of obesity. Evidence from clinical trials using vitamin D supplementation to achieve weight reduction is limited. Some trials, however, have suggested that concomitant supplementation with vitamin D and calcium potentially reduces central fat deposits, especially in individuals with low dietary calcium intakes. Adiposity has important implications for the efficacy of vitamin D supplementation, and increases in 25(OH)D concentrations are generally lower in obese than in normal-weight individuals. Active hormonal vitamin D has many mechanistic effects, both physiologically and biochemically, that could counteract the harmful effects of obesity on metabolism and reduce the risks of metabolic abnormalities and tissue damage consequent to adiposity. Whether improvements in the overall obesogenic metabolic profile can be achieved by vitamin D supplementation, however, is still unknown.