Adiposity in the Relationship between Serum Vitamin D Level and Insulin Resistance in Middle-Aged and Elderly Korean Adults: The Korea National Health and Nutrition Examination Survey 2008.

Background: The role of adiposity in the relationship between serum vitamin D levels and insulin resistance has not yet been fully studied. This aim of this study is to clarify the role of adiposity in the relationship between serum vitamin D level and insulin resistance among middle-aged and elderly Korean adults.

Methods: We used data from 2,710 individuals aged ≥50 years based on national data from a representative sample of the fourth Korea National Health and Nutrition Examination Survey IV-2 in 2008.

Results: After adjustment for potential confounders, body mass index (BMI) was significantly associated with 25(OH) vitamin D (P=0.008). However, waist circumference was not significantly associated with 25(OH) vitamin D. In the stratified analyses, 25(OH) vitamin D was found to be negatively associated with fasting insulin and homeostasis model assessment estimate of insulin resistance (HOMA-IR) in participants with BMIs ≥25 kg/m(2) (P=0.003 for both insulin and HOMR-IR) but was not found to be associated in those with BMIs <23 kg/m(2). However, we observed a significant inverse in the association of 25(OH) vitamin D with fasting insulin and HOMA-IR in both the normal (P=0.001 and P<0.001 and the abdominally obese group (P=0.010 and P=0.009) in the stratified analyses according to abdominal obesity.

Conclusion: Our results support that the idea that endogenously-produced vitamin D might be stored in subcutaneous fat deposits. In addition, the association of vitamin D with insulin resistance in middle-aged and elderly Korean adults was stronger when it was stratified by BMI than when abdominal obesity status.