Association between vitamin D status and insulin resistance in Korean adolescents: differential effects of obesity using non-insulin-based indices

OBJECTIVE: This study evaluated the relationship between vitamin D status and insulin resistance (IR) among Korean adolescents, focusing on the differences between normal-weight and overweight/obese groups using non-insulin-based IR indices. METHODS: In this cross-sectional study, data from 3,838 adolescents (age: 12-18 years) who participated in the Korea National Health and Nutrition Examination Survey (KNHANES) from 2008 to 2014 were included. Using this nationally representative dataset, serum 25-hydroxyvitamin D (25(OH)D) levels were measured, and the prevalence of vitamin D deficiency (25(OH)D < 20 ng/mL) was estimated at the population level. The subjects were divided into the normal-weight and overweight/obese groups. We used the triglyceride-glucose index (TyG), triglyceride-to-high-density lipoprotein cholesterol ratio(TG/HDL-C), TyG with body mass index (TyG-BMI), and metabolic score for IR (METS-IR) as non-insulin-based IR indices. To evaluate the mean differences between groups and the associations with vitamin D status, we used a survey-weighted generalized linear regression model, adjusting for age, sex, household income, and strength training. RESULTS: The prevalence of vitamin D deficiency among adolescents was 78.5%. In particular, the mean vitamin D levels were higher in boys, individuals who engaged in strength training, and individuals with waist circumferences below the 90th percentile. Vitamin D levels were significantly negatively associated with IR markers, particularly METS-IR in the normal-weight group and TyG-BMI and METS-IR in the overweight/obese group. The sensitivity analysis revealed that higher vitamin D levels were associated with a more substantial reduction in IR, especially in overweight/obese adolescents. CONCLUSIONS: Vitamin D deficiency is significantly associated with higher IR in adolescents, as measured by non-insulin-based indices. This association appears to be strong in overweight/obese individuals.