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.