Association between serum 25-hydroxyvitamin D levels and cardiometabolic index among overweight/obese U.S. adults: A cross-sectional study.

Obesity is a major driver of cardiovascular disease (CVD) risk, with the cardiometabolic index (CMI) serving as a novel indicator. While vitamin D's potential protective role against CVD is recognized, its precise dose-response relationship with CMI in high-risk overweight/obese individuals remains unclear. This study aimed to systematically evaluate the association between serum 25-hydroxyvitamin D (25(OH)D) levels and CMI in overweight/obese U.S. adults and characterize its dose-response pattern. A cross-sectional analysis was conducted using data from the National Health and Nutrition Examination Survey 2009 to 2018, including 6597 overweight/obese participants aged 18 to 64 years. Serum 25(OH)D levels were categorized into 3 groups: sufficient (≥75 nmol/L), insufficient (50-74 nmol/L), and deficient (<50 nmol/L). CMI was calculated as (triglycerides/high-density lipoprotein cholesterol) × waist-to-height ratio. Multivariable linear regression models were employed to assess the association of 25(OH)D with CMI. Restricted cubic splines and likelihood ratio tests for piecewise regression were used to rigorously test for nonlinearity. Subgroup analyses and interaction tests were performed to evaluate the heterogeneity of the association across different populations. After comprehensive adjustment, serum 25(OH)D levels were significantly and independently associated with CMI in a negative linear manner (β = -0.09, 95% CI: -0.14 to -0.05, P <.001). Compared to the sufficient 25(OH)D group, the deficient group had a significantly higher CMI (β = 0.19, 95% CI: 0.10 to 0.28, P <.001). Both restricted cubic splines (P for nonlinearity = 0.389) and LRT (P = .346) did not support a nonlinear association. Notably, this negative association was significantly stronger in participants with diabetes (P for interaction = 0.038). The effect size (β = -0.21, 95% CI: -0.37 to -0.05) was more than 3 times that of the nondiabetic population (β = -0.06, 95% CI: -0.11 to -0.02) (P for interaction = 0.038). This study found that in overweight/obese U.S. adults, higher serum 25(OH)D levels are linearly associated with better cardiometabolic health (lower CMI), with this association being more pronounced in individuals with diabetes. These findings suggest that improving vitamin D status may be a potential public health strategy for mitigating cardiometabolic risk in the overweight/obese population.