Serum vitamin D levels and their association with glycemic control and insulin resistance in type 2 diabetes

Abstract

Numerous studies have demonstrated the role of vitamin D in patients with type-2 diabetes mellitus (T2DM), but evidence regarding its association with glycemic control and insulin resistance among T2DM patients in Indonesia is still limited. This study investigated the association between serum 25-hydroxyvitamin-D [25(OH)D] levels, glycemic control, and insulin resistance among patients with T2DM. A cross-sectional study was conducted among 129 T2DM patients aged 30–80 years in Semarang, Indonesia. Serum 25(OH)D and insulin levels were measured using ELISA, fasting plasma glucose (FPG) with the GOD-PAP method, glycated hemoglobin (HbA1c) using enzyme immunoassay, and insulin resistance assessed with HOMA-IR. Correlation tests and multivariate linear regression analyses were performed, adjusting for age, body mass index, and sex. Vitamin D deficiency was found in 48.8% of subjects, predominantly in females. Serum 25(OH)D levels were inversely correlated with HbA1c (r = –0.257, p = 0.003) and FPG (r = –0.173, p = 0.050). After adjustment, significant negative associations remained for HbA1c (B = –0.020, p = 0.009) and FPG (B = –0.942, p = 0.007). Sex-stratified analyses showed that these inverse associations were significant only in females, while in males, 25(OH)D was positively associated with fasting insulin. No significant relationship was found between 25(OH)D and HOMA-IR. These findings suggest that serum vitamin D levels are associated with glycemic control in patients with T2DM, with potential sex-specific differences, underscoring the need to consider vitamin D status in diabetes management strategies.