Relationship of serum vitamin D levels with diabetic microvascular complications in patients with type 2 diabetes mellitus

BACKGROUND: Vitamin D deficiency has been reported to be associated with diabetic microvascular complications, but previous studies have only focused on the relationship between vitamin D and specific complications. Therefore, we aimed to explore the relationship between vitamin D level and diabetic microvascular complications in general, including diabetic retinopathy (DR), diabetic nephropathy (DN), and diabetic peripheral neuropathy (DPN). METHODS: This was a cross-sectional study of 815 patients with type 2 diabetes mellitus (T2DM). Clinical information and laboratory results were collected from the medical records. The relationship between vitamin D and the three diabetic microvascular complications was investigated. RESULTS: The serum 25-hydroxyvitamin D (25 [OH] D) level of patients with DPN and/or DN was significantly lower than that of T2DM patients without any microvascular complications (P < 0.01). Univariate analysis showed that the 25 (OH) D level was related to DPN and DN, but not DR. After adjustment, the 25 (OH) D level was confirmed to be an independent protective factor for DPN (odds ratio [OR]: 0.968, P = 0.004]) and DN (OR: 0.962, P = 0.006). The prevalence of DPN and DN increased significantly as the serum 25 (OH) D levels decreased. Furthermore, patients with both DPN and DN had the lowest concentration of serum 25 (OH) D (P < 0.001), and the prevalence of macroalbuminuria increased more abruptly than that of microalbuminuria across the 25 (OH) D tertiles. Among the patients with vitamin D insufficiency, those with DPN presented more comorbid macroalbuminuria than those without DPN (15.32% vs. 4.91%; P = 0.001). CONCLUSIONS: Vitamin D deficiency is independently associated with higher risk of DPN and DN, but not DR, in T2DM patients. Further, it may be a potential predictor for both the occurrence and severity of DPN and DN.