Fat Distribution as a Determinant of Vitamin D Status: A Cross-Sectional Study of Adults in the United States.

Background: This study aimed to elucidate correlations between obesity-related indicators and vitamin D (VD) status in a nationally representative sample of U.S. adults.

Methods: We analysed data from 9168 adults aged 20-59 years obtained from the 2011-2018 National Health and Nutrition Examination Survey. Serum 25 hydroxyvitamin D [25(OH)D] levels were measured and categorised into quartiles. Anthropometric measurements, including weight, waist circumference, and fat mass in various body regions quantified through dual-energy X-ray absorptiometry, were collected. Multiple imputation was employed to replace missing data. The importance of obesity-related indicators and serum 25(OH)D concentration was explored using multiple linear regression adjusted for demographics, lifestyle factors, dietary intake, and clinical biomarkers, and stepwise regression.

Results: Weight, waist circumference, and fat mass across all body regions were inversely associated with serum 25(OH)D levels (all p < 0.001). Notable differences were observed between men and women. Stepwise regression revealed a strong inverse correlation between visceral adipose tissue and serum 25(OH)D concentration in men [β 95% CI: -13.04 (-18.10, -7.99), p < 0.001], whereas in women, only weight was significantly correlated with serum 25(OH)D concentration [β 95% CI: -0.20 (-0.28, -0.12), p < 0.001]. Demographic attributes, seasonal sunlight exposure, dietary VD, calcium, phosphorus, and magnesium intake, and biomarkers including alkaline phosphatase and creatinine also emerged as significant predictors.

Conclusions: Besides conventional obesity measures, abdominal fat metrics exhibit robust associations with VD deficiency, especially in men. Public health initiatives and clinical management strategies for hypovitaminosis D in obese populations should consider nuanced aspects of adiposity distribution alongside other demographic, lifestyle, and dietary factors influencing VD.