DM and its related complications are increasing worldwide. DPN is considered a major micro-vascular complication, which is estimated to affect up to half of these diabetic patients and represent a main cause of mortality and morbidity in these patient. The complex pathogenesis of DPN is still not clear [8]. However, increased blood glucose level, decreased blood flow, hypoxia, hypoxia-induced pro-angiogenesis, and pro-inflammatory responses may play an important role in the pathogenesis. Moreover, pro-inflammatory cytokines, like interleukins, affect nerves and glial cells and are supposed to be involved in the pathology of diabetic neuropathy. Vitamin D deficiency is linked to the presence of inflammation and hyperglycemia, so it could be considered as a high risk factor for DPN [9].
The current study was conducted on 80 patients with type 2 DM aiming to evaluate the association between vitamin D level and diabetic neuropathy development and to assess if there is a relationship with certain subtypes of diabetic neuropathy.
In the current study, we found that 100% of lower limb nerves are affected in patient groups and this affection is seen mostly in sensory nerves, which is in accordance with the rule that diabetic neuropathy affects mostly long sensory nerves earlier and this is in accordance with Vinik and colleagues [10].
We found that common peroneal nerve involvement predominates and this was supported by Kong and his colleagues [11], while Kakrani and colleagues [12] assumed that tibial nerve involvement is more likely to be found in DPN.
Our results are in agreement with a study of Shillo and his colleagues [13], who studied vitamin D level in patients with painful DPN, painless DPN, and diabetics without DPN and it showed that significant deficiency in patients with painful DPN more than patients with painless DPN and those without DPN.
In addition, this was in accordance with a previous study of Usluogullari and coauthors [14], who evaluated vitamin D level in 557 patients having type two diabetes and healthy controls randomly selected and revealed that vitamin D deficiency is more common in diabetic patients with micro-vascular complications including neuropathy. Vitamin D levels were found to be lower in patients in whom these complications were more severe.
In a study of Oraby and colleagues [15], who compared patients with DPN to healthy controls, vitamin D deficiency was found to be a suspected risk factor for DPN as the results of this study ensured that vitamin D levels in DPN patients were lower than those in the control group, especially in patients with severe neuropathy.
Also, Martin and colleagues [16] tried to assess the effectiveness of vitamin D supplementation on patients with DPN and found that vitamin D supplementation together with exercise reduced both symptoms and complications of DPN. As well, Papanas and Ziegler [17] analyzed risk factors for DPN in a major study and they concluded that vitamin D deficiency had a significant risk factor for development of DPN.
Moreover, Qu and his colleagues [18] directed a meta-analysis to evaluate the role of vitamin D deficiency in DPN over ten studies. They found that vitamin D level was significantly reduced in patients with DPN, but more in Caucasian than Asian races. This meta-analysis also assumed that it is clear that vitamin D is involved in the development of DPN, and vitamin D deficiency is very likely to be associated with increased risk of DPN. Appropriate vitamin D supplements also can be an effective tool to delay the development of DPN in diabetic patients.
Furthermore, another study was done by Greenhagen and colleagues [19] to evaluate vitamin D in patients with diabetic foot complications. In 100 patients involved in the study, it was found that 75% of patients had vitamin D deficiency, but no significant difference between patients with Charcot joints and those without. In another meta-analysis by Zhang and coauthors [20], involving more than 13 studies including about 2800 patients all with type two diabetes, heterogeneity test showed significant relation between vitamin D and development of DPN in T2DM patients. Most previous studies confirmed that there was vitamin D deficiency in diabetic patients with DPN. Also, more studies are needed to evaluate the definitive role of vitamin D deficiency in development of DPN.
There were no previous studies confirming the results against our study.