Randomized, Double-Blind, Placebo-Controlled Study to Assess the Effect of Vitamin D in Patients With Diabetic Peripheral Neuropathy to Alleviate Pain and Improvement of Symptoms

Diabetic peripheral neuropathy is one of the common complications of long-standing diabetes mellitus with a prevalence of 30% to 50%. It accelerates the occurrence of ulcers of diabetic foot and amputation of lower extremities as well as severely affects the quality of life. The treatment of this condition has remained unsatisfactory in spite of a good response to conventional medications. Studies showed that Vitamin D3 exerts a neuroprotective effect through the production of nerve growth factor (NGF) and neurotrophins. However, some recent trials demonstrated that vitamin D3 could be a promising agent in this regard. This proposed study was therefore an effort whether there is any role of vitamin D3 in improving symptoms of diabetic peripheral neuropathy patients. This study was a randomized, double-blind, placebo-controlled trial, conducted in the Department of Pharmacology in collaboration with the Department of Endocrinology of Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka from September 2019 to January 2022. A total of 72 patients suffering from diabetic peripheral neuropathy was enrolled according to inclusion and exclusion criteria. A validated version of the Michigan Neuropathy Screening Instrument (MNSI) and Visual Analogue Scale (VAS) was used to assess peripheral neuropathy. Then the patients were randomly allocated into two arms: control and intervention. The patient in the control arm received the standard antidiabetic medications plus one placebo capsule weekly orally for 8 weeks starting from the day of an initial assessment. On the other hand, the intervention arm received the standard antidiabetic medications plus one capsule of vitamin D3 (40,000 IU) weekly orally for 8 weeks starting from the day of an initial assessment. Data of HbA1c level was recorded and a blood sample was collected to measure serum 25(OH) D level at baseline and after 8 weeks of therapeutic intervention. Confirmation of the regular intake of medicine was ensured over the telephone, pill count, and from the patient's compliance sheet. After 8 weeks each patient was evaluated again using VAS and MNSI tools. Out of 72, 53 patients had completed the study and met the criteria for analysis. Therefore, Intention to Treat (ITT) was 72 and Per Protocol (PP) treatment was 53. The statistical tests used to analyze the data were the chi-square (x2) test, paired t-test, unpaired t-test, and Pearson correlation test. The chi-square (x2) test was used to compare categorical data between two groups. The independent t-test was used to compare the continuous data between two groups. P-value ≤ 0.05 was considered significant. After 8 weeks of treatment, the VAS score of pain in DPN patients in the intervention arm reduced significantly (P=0.00) from 5.50 ± 0.64 to 4.23 ± 0.98. In the intervention arm, statistically significant improvement was also observed in the MNSI score both for the questionnaire (from 8.54 ± 1.15 to 6.00 ± 1.32; P=0.00) and physical assessment (from 3.44 ± 1.22 to 2.40 ± 1.06; P=0.00) respectively. Serum 25(OH)D level significantly improved (P=0.00) after oral administration of vitamin D3 in the intervention arm from 10.83 ± 4.47 ng/ml to 17.79 ± 7.53 ng/ml. The reduction observed in HbA1c level in the intervention arm (from 8.66 ± 1.39 to 7.25 ± 0.87) was significant (P=0.00). This should be noted that a significant reduction of VAS score (P= 0.04) and MNSI questionnaire score (P=0.00) was observed in the placebo arm after 8 weeks, though the difference between the reduction achieved was significant between placebo and intervention arm (for VAS, P=0.00 and for MNSI, P=0.00). However, in the control arm, there was no significant reduction (P=0.69) in MNSI physical assessment score. A negative correlation was observed between serum 25(OH) D level and VAS (r= -0.1) and MNSI score (r= -0.17) respectively. Oral administration of 40,000 IU vitamin D3 weekly for 8 weeks along with standard antidiabetic medications produces a significant reduction of the level of pain and other neuropathic symptoms in the patients with Diabetic Peripheral Neuropathy.