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

Abstract

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 (HEIdairy) to Index I through 25(OH)D and %BF indicated complete mediation among the CO- group, but HEIdairy 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.

Figures

Figure 1

Flow diagram for study sample selection, NHANES 2001–2004.

Figure 2

SM stratified by central obesity (CO) status: testing mediation of HEI-Index I MetD through 25(OH)D and %BF. A theoretical model was set up in which sociodemographic and lifestyle factors were exogenous to the main variables of interest. The model consisted of simultaneous equations with outcomes being HEI, 25(OH)D, %BF, and number of MetD (Index I range between 0 and 7), stratified by central obesity status. HEItotal and HEIdairy were considered alternatively. Effect modification by central obesity status was determined for the main associations of interest by comparing 95% CI of path coefficients. The following equations correspond to the general setup of the structural equations model: 1 2 3 4 where HEI (total or dairy component; z-score) was allowed to predict all subsequent outcomes, plasma 25(OH)D level (vitamin D; z-score) was allowed to predict only %BF and number of MetD (Index I; ordinal), and BF was allowed to predict only MetD. Zj is the vector of other exogenous variables (e.g. sociodemographic and lifestyle factors; continuous terms such as age were entered as continuous), whereas e1, e2, e3, and e4 are the error terms. Correlations between all exogenous variables except error terms (assumed to be zero) were estimated.

Figure 3

Mean difference in 25(OH)D by central obesity status (CO+ or CO−): OLS multiple linear regression findings (β with 95% CI), adjusting for sociodemographic, lifestyle, dietary factors, and % BF (NHANES 2001–2004). *, P < 0.05 for null hypothesis that adjusted β = 0 from OLS multiple linear regression, Wald test. For model 1, 25(OH)D is regressed on central obesity, adjusted for age and sex (n = 8184); model 2 adjusted for all sociodemographic, lifestyle, and dietary variables (see Covariates in Materials and Methods) (n = 7300); and model 3 further adjusted for %BF (n = 7278).