Serum 25-hydroxyvitamin D levels and peripheral neuropathy in patients with type 2 diabetes: a systematic review and meta-analysis

Vitamin D is a multifunctional pro-hormone and has widespread actions in human body. Several studies showed a possible association between vitamin D deficiency and diabetic peripheral neuropathy (DPN) in patients with type 2 diabetes, but no definite conclusion was available. A systematic review and meta-analysis was performed to comprehensively assess the association between serum 25-hydroxyvitamin D [25(OH)D] levels and DPN in patients with type 2 diabetes. Data from eligible studies were pooled using meta-analysis. Six studies that involved a total of 1,484 type 2 diabetic patients were finally included into the meta-analysis. Meta-analysis showed that there were obviously decreased serum 25(OH)D levels in DPN patients [weighted mean difference (WMD) = −6.36 ng/ml, 95 % confidence interval (95 % CI) −8.57 to −4.14, P < 0.00001]. Vitamin D deficiency was also significantly associated with increased risk of DPN in patients with type 2 diabetes [odds ratio (OR) 2.88, 95 % CI 1.84–4.50, P < 0.00001]. Meta-analysis of three studies with adjusted estimates showed that vitamin D deficiency was independently associated with increased risk of DPN in patients with type 2 diabetes (OR 2.68, 95 % CI 1.67–4.30, P < 0.0001). Sensitivity analysis showed that there was no obvious change in the pooled estimates. Vitamin D is involved in the development of DPN in type 2 diabetic patients, and vitamin D deficiency is very likely to be associated with DPN in type 2 diabetic patients. Further studies are needed to validate the association between vitamin D deficiency and DPN.