25-hydroxyvitamin D is associated with islet function homeostasis in type 2 diabetes patients with abdominal obesity

Aim: Islet α-cells input is essential for insulin secretion from β-cells. The role 25-hydroxyvitamin D (25(OH)D) on islet α-cells function is unclear. We aimed to investigate the association between 25(OH)D and islet function homeostasis in type 2 diabetes (T2D) patients. Methods: : Total 4670 T2D patients were enrolled from seven communities in Shanghai, China. Anthropometric indices, biochemical parameters, serum 25(OH)D, and islet function including C-peptide (C-p) and glucagon were measured. Results: : With increase in 25(OH)D level, FPG, HbA1c, glucagon and C-p were significantly decreased in trend in T2D patients. The population were divided into abdominal obesity and non-abdominal obesity group. 25(OH)D level was associated with HbA1c, glucagon and HOMA-β in non-abdominal obesity group after adjustment. As for abdominal obesity group, there was the significant association between 25(OH)D and HbA1c, glucagon, HOMA-IR, baseline insulin and C-p. The OLS regression and quantile regression further showed that 25(OH)D was associated with glucagon and fasting C-p levels in T2D patients with abdominal obesity. In non-abdominal obesity group, the OLS regression showed that the regression coefficients were not significant in 50th percentile for HOMA-β. The moderate analyses revealed significantly interaction effect of 25(OH)D and glucagon on C-p ( P =0.0124), as well as the effect of 25(OH)D and duration of diabetes on glucagon/C-p in abdominal obesity group. According to the range of the duration of diabetes, the conditional indirect effect of 25(OH)D on glucagon/C-p was significantly at 1 SD below the mean ( P =0.0002) and the mean of the duration of diabetes ( P =0.0007). Conclusion: 25(OH)D was negatively associated with glucagon and C-p in T2D patients with abdominal obesity. Duration of diabetes influence the effect of 25(OH)D on the ratio of glucagon/C-p, on behalf of islet function homeostasis, in T2D patients with abdominal obesity.