Associations between Vitamin D Levels and Insulin Resistance in Non-Diabetic Obesity: Results from NHANES 2001-2018.

Objective: Obesity is often accompanied by insulin resistance (IR) and diabetes. We explored the association between vitamin D levels and IR in non-diabetic obesity.
Methods: We conducted a cross-sectional study based on the data of National Health and Nutrition Examination Survey (NHANES) from 2001 to 2018. Non-diabetic individuals (aged ≥20 years) with obesity (BMI ≥ 30kg/m ² ) were included in the study. And HOMA-IR ≥ 2.5 was defined as IR. The multivariable linear regression models were constructed to evaluate the associations between levels of 25(OH)D and HOMA-IR. We calculated the odds ratio (OR) and 95% confidential intervals (CIs) for associations between 25(OH)D deficiency and IR in obesity using multivariable logistic regression models.
Results: Overall, a total of 3887 individuals were included in this study. Serum vitamin D level was significant lower in obesity participants with IR than that of non-IRs. The linear regression models showed that vitamin D level was inversely associated with HOMA-IR in obesity after adjusting for covariables (β=-0.15, 95%CI (-0.28, -0.02), p  = 0.028). And the multivariable logistic regression models indicated an association between vitamin D deficiency and IR in obesity ((OR= 1.38, 95%CI (1.09-1.73), p  = 0.007)). The further stratified regression analyses among different BMI demonstrated that vitamin D deficiency (OR = 1.4, 95%CI (1.05,1.86), p  = 0.022) only contributed to developing IR in class I obesity.
Conclusion: This study suggested an association of vitamin D levels with IR in obesity. And vitamin D deficiency contributed to IR in class I obesity.