The association between vitamin D level and diabetic peripheral neuropathy in patients with type 2 diabetes mellitus: An update systematic review and meta-analysis.

AIM: Recently, increasing studies have been carried out to explore the association between vitamin D level and the development of diabetic peripheral neuropathy (DPN) in patients with diabetes mellitus (DM). However, because of the shortcoming in study design and sample size, there is still no clear conclusion. We performed this meta-analysis to examine the exact impact of vitamin D deficiency on DPN in type 2 diabetic patients.

METHODS: Various databases were searched to identify the potential articles which explored the association between vitamin D level and diabetic peripheral neuropathy in type 2 diabetes. We pooled OR to assess the correlation between vitamin D deficiency and DPN using the random-effects model. The standardized mean difference (SMD) with 95% CI of vitamin D was also calculated to evaluate the vitamin D level between DPN and non DPN in T2DM.

RESULTS: There was obvious heterogeneity in those included ten studies (I2  = 94.1%, Cochran Q test P < 0.001) using mean and standard deviation (SD) of vitamin D level. In Caucasian, vitamin D level was significantly lower in DPN patients compared with diabetic patients without DPN (SMD = -0.56, I2  = 16.9%). In Asian, the pooled OR value of vitamin D deficiency was 1.22 (95%CI: 1.17-1.27). Sensitivity analysis showed one study had great influence on this meta-analysis and it still existed after excluded that one. There was no evidence of public bias in meta analysis as showed in Begg test and Egger test.

CONCLUSION: This meta-analysis indicates that vitamin D deficiency is associated with the generation and development of DPN in Caucasian with T2DM, and in Asian, diabetic patients with vitamin D deficiency are 1.22 times to suffer from DPN compared with normal vitamin D level. Vitamin D supplementation is urgently needed to prevent the development of DPN in T2DM.