The impact of vitamin D supplementation on peripheral neuropathy in a sample of Egyptian prediabetic individuals [version 2; peer review: 2 approved]

Background: Vitamin D deficiency is seen more frequently in diabetic patients with distal symmetrical polyneuropathy. Unfortunately, there is a shortage of data concerning prediabetic individuals with peripheral neuropathy (PN). Therefore, we aimed to study the association of vitamin D deficiency with PN severity and to determine the effect of vitamin D supplementation on PN in prediabetics. Methods: A case-control study was conducted consisting of 89 prediabetic individuals with PN and a control group of prediabetics without PN, recruited from the outpatient department of the National Institute of Diabetes and Endocrinology, Cairo, Egypt. All patients were screened for PN using clinical examination and Douleur Neuropathique 4 diagnostic questionnaire (DN4). Group A (with PN) was assessed for neuropathic severity using the Short-Form McGill Pain Questionnaire (SF-MPQ). In addition, 25-hydroxyvitamin D, ionized calcium, phosphorus, parathyroid hormone (PTH), glycated hemoglobin (HbA1c), fasting blood glucose (FBG), 2-hour post 75g glucose (2h-PPBG) and lipid profile were measured for both groups. Prediabetic patients with PN were given vitamin D3 200.000 IU IM monthly for three months. After three months, clinical assessment, DN4, SF-MPQ and all laboratory measures were repeated. Results: Vitamin D was not associated with the severity of PN patients. However, supplementation of vitamin D resulted in a highly significant improvement in glycemic parameters , p≤0.001. Interestingly, neuropathy score and severity before vitamin D supplementation were (6.4±1.6 and 28.3±7.2) and after became (2.5±0.9 and 17±6.3, p≤0.001). Conclusion: Correction of vitamin D deficiency in prediabetics with PN as well as hypovitaminosis D, improves glycemic parameters, PN score and severity.