Urban-rural differences explain the association between serum 25-hydroxyvitamin D level and insulin resistance in Korea.

Bo Song,Young Yoon,Yumie Rhee,Yoosik Youm,Eun Lee,Ju-Mi Lee,Kyoung Kim,Chang Kim,Hyeon Kim

doi:10.3390/nu6125806

Abstract

An increasing number of studies report associations between low serum 25-hydroxyvitamin D [25(OH)D] level and insulin resistance; however, whether low vitamin D levels directly contribute to increased insulin resistance is unclear. We investigated the impact of residential area on the association between 25(OH)D and insulin resistance in elderly Koreans. Using data from the Korean Urban Rural Elderly study, we conducted cross-sectional analyses in 1628 participants (505 men and 1123 women). Serum 25(OH)D was analyzed as both continuous and categorized variables. Homeostasis model assessment for insulin resistance (HOMA-IR) was calculated using fasting blood glucose and insulin levels. In men, 25(OH)D level was inversely associated with HOMA-IR (standardized β = −0.133, p < 0.001) after adjustment for age, body mass index, waist circumference, smoking, alcohol intake, exercise, and study year. However, we noted significant urban-rural differences in 25(OH)D level (43.4 versus 65.6 nmol/L; p < 0.001) and HOMA-IR (1.2 versus 0.8 mmol·pmol/L2; p < 0.001). When we additionally adjusted for residential area, the association between 25(OH)D and HOMA-IR was attenuated (standardized β = −0.063, p = 0.115). In women, the association between 25(OH)D and HOMA-IR was not significant before or after adjustment for residential area. Environmental or lifestyle differences in urban and rural areas may largely explain the inverse association between serum 25(OH)D and insulin resistance.

Highlights

Vitamin D plays important roles in calcium and phosphate absorption in the intestine, sustaining sufficient concentrations thereof in the blood
Mean Body mass index (BMI) was significantly lower in men than in women; mean waist circumference was significantly higher in men than in women
When we assessed the association between serum 25(OH)D and Homeostasis model assessment for insulin resistance (HOMA-IR), stratified by residential area, we found no significant association for either urban or rural participants (Table 6)

Summary

Introduction

Vitamin D plays important roles in calcium and phosphate absorption in the intestine, sustaining sufficient concentrations thereof in the blood. Access to these minerals at bone-forming sites makes normal mineralization of bone possible [1,2]. Studies from Asian countries, with a few exceptions, have reported a high prevalence of vitamin D deficiency in both sexes and all age groups [4,5,6,7,8,9,10]. Several studies have reported that low serum 25-hydroxyvitamin D [25(OH)D] may be significantly associated with increased insulin resistance [1,15,16]. Whether or not low serum vitamin D concentrations directly contribute to the development of insulin resistance remains controversial

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Conclusion