Relationship of serum 25-hydroxyvitamin D with the metabolic score for insulin resistance in Korean adults.

Vitamin D has been linked to insulin sensitivity and glucose metabolism. However, few studies have separately examined the association between serum 25-hydroxyvitamin D2 (25(OH)D2) and 25-hydroxyvitamin D3 (25(OH)D3) levels and insulin resistance. Therefore, we investigated the associations of serum 25(OH)D2, 25(OH)D3, and total 25-hydroxyvitamin D (25(OH)D) levels with the metabolic score for insulin resistance (METS-IR) in a nationally representative sample of Korean adults. This cross-sectional study analyzed data from 9,297 adults aged ≥19 years who participated in the 2022-2023 Korea National Health and Nutrition Examination Survey. Linear regression was used to examine the associations of serum 25(OH)D2, 25(OH)D3, and total 25(OH)D levels with the METS-IR. Total 25(OH)D (β = -0.0843, 95% confidence interval [CI]: -0.0995 to -0.0691) and 25(OH)D3 levels (β = -0.0831, 95% CI: -0.0983 to -0.0680) showed significant, linear inverse associations with the METS-IR. However, serum 25(OH)D2 levels were not significantly associated with the METS-IR. Stratified analyses revealed that the inverse association between the 25(OH)D3 level and METS-IR was significantly stronger in participants with obesity, diabetes mellitus, or hypercholesterolemia than in their counterparts. These findings were consistent across all the sensitivity analyses. In this nationally representative study of Korean adults, total 25(OH)D and its principal component 25(OH)D3 were inversely associated with the METS-IR. In contrast, 25(OH)D2 was not associated, a finding most likely attributable to its very low circulating concentrations. Because total 25(OH)D performed comparably to 25(OH)D3, it remains a practical measure of vitamin D status in metabolic care.