Standardized serum 25-hydroxyvitamin D concentrations are inversely associated with cardiometabolic disease in US adults: a cross-sectional analysis of NHANES, 2001-2010

Background: Previously reported associations between vitamin D status, as measured by serum 25-hydroxyvitamin D [25(OH) D] concentrations, and cardiometabolic risk factors were largely limited by variability in 25(OH) D assay performance. In accordance with the Vitamin D Standardization Program, serum 25(OH) D measurement was recently standardized in the National Health and Nutrition Examination Survey (NHANES) to reduce laboratory and method related differences in serum 25(OH) D results. We evaluated the overall and ethnic-specific associations between the newly standardized serum 25(OH) D concentrations and cardiometabolic risk in U.S. adults. Methods: This study examined standardized 25(OH) D data from five cycles of the NHANES (2001-2010). The total sample included 7674 participants (1794 Mexican-Americans, 4289 non-Hispanic whites, and 1591 non-Hispanic blacks) aged >= 20 years who were examined in the morning after overnight fasting. Serum 25(OH) D was directly measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in 2007-2010, and was predicted from LC-MS/MS equivalents for 2001-2006. Serum 25(OH) D levels were categorized into quartiles (< 43.4, 43.4-58.6, 58.7-74.2, >= 74.3 nmol/L). Cardiometabolic risk was defined by the homeostatic model assessment of insulin resistance (HOMA-IR), metabolic syndrome (MetS), and Framingham cardiovascular disease (CVD) risk. Prevalence ratios and 95% confidence intervals were calculated using modified Poisson regression. Results: After full adjustment for confounders, serum 25(OH) D >= 74.3 nmol/L was associated with lower cardiometabolic risk compared to 25(OH) D < 43.4 nmol/L in the overall sample [HOMA-IR: 0.70 (0.59, 0.84); MetS: 0.82 (0.74, 0.91); CVD risk: 0.78 (0.66, 0.91)]. These associations remained significant in Mexican-Americans [HOMA-IR: 0.54 (0.35, 0.82); MetS: 0.73 (0.55, 0.96)], non-Hispanic whites [HOMA-IR: 0.81 (0.68, 0.96); MetS: 0.84 (0.73, 0.95); CVD risk: 0.78 (0.64, 0.93)]; and in non-Hispanic blacks [HOMA-IR: 0.67 (0.45, 0.99); MetS: 0.75 (0.56, 0.97); CVD risk: 0.58 (0.41, 0.81)]. Conclusions: Low vitamin D status is a significant risk factor for cardiometabolic disease in U.S. adults based on standardized serum 25(OH) D results, irrespective of ethnic background. Future studies using standardized 25(OH) D data are needed to confirm these results, particularly amongst U. S. blacks with 25(OH) D concentrations above 75 nmol/L.