Associations among 25-hydroxyvitamin D, diet quality, and metabolic disturbance differ by adiposity in adults in the United States

Context: Recent evidence indicates that a higher plasma level of 25-hydroxyvitamin D [25(OH)D] is associated with lower adiposity and a reduced number of metabolic disturbances (MetD). Objectives: We examined associations among dietary quality, 25(OH)D, percent body fat (%BF), and MetD, and a pathway linking them, across central obesity. Design: This cross-sectional nationally representative study used extensive data from the National Health and Nutrition Examination Surveys of 2001-2004. Participants: U.S. adults aged at least 20 yr were stratified by central obesity (CO) status. Sample sizes ranged from 1943 (all MetD combined) to 7796 (each component). Main Outcome Measures: %BF was measured using dual-energy x-ray absorptiometry, and MetD was measured with individual continuous nonadiposity outcomes (e.g. fasting plasma glucose) and with a composite count index of binary MetD with prespecified cutoff points (Index I). Results: A higher 25(OH)D was associated with better dietary quality, lower %BF, and lower number of MetD. These inverse 25(OH)D-%BF and 25(OH)D-MetD associations (i.e. fasting blood glucose, homeostatic model assessment of insulin resistance, C-reactive protein, and Index I) were significantly stronger among the CO⁺ group. Finally, the pathway linking the dairy component of the Healthy Eating Index (HEI_dairy) to Index I through 25(OH)D and %BF indicated complete mediation among the CO^- group, but HEI_dairy and 25(OH)D had direct inverse associations with Index I among the CO⁺ group. Conclusions: Due to potential genetic differences between CO^- and CO⁺ groups, empowering U.S. adults with central obesity to make related behavioral changes may be especially effective in improving their vitamin D status and metabolic profile.