The Role of Vitamin D Levels in Patients with Painful Diabetic Neuropathy

Rebekka Schrecengost, Pharm.D., Essentia Health 

Background: Low vitamin D levels have been linked to numerous health conditions including diabetic peripheral neuropathy (DPN). Vitamin D’s role in pain may be attributed to its action in the small nerve fibers of the dorsal root ganglia.

Purpose: The study by Shillo et al. sought to further differentiate patients with painful and painless neuropathy to investigate if there was a significant difference in 25-hydroxyvitamin D levels in patients with differing severities of DPN.

Study Design: The study included 59 white Europeans into four groups – patients without diabetes (n=14), Type 2 diabetes with no neuropathy (n=14), painless DPN (n=14), and painful DPN (n=17). Patients were placed in the different groups using standardized neuropathy assessment tools. Participants completed a sunlight exposure questionnaire, vitamin D assay, and skin biopsy procedure.

Results: Compared to healthy volunteers and the no-DPN and DPN groups had a higher mean BMI (P=0.02, DPN M=32.8 mg/kg2, no-DPN M=30.1 mg/kg2, healthy M=26.1 mg/kg2), were older (P=0.009, DPN M=61.8 years, no-DPN=55.4 years, healthy M=52.1 years), and had longer median duration of diabetes (DPN m=15 years, no-DPN m=6.5 years); but there were no significant differences in HgbA1c or estimates of sunlight exposure between groups (P=0.63). After adjusting for age, BMI, activity score and sunlight exposure, vitamin D levels were significantly lower in the 17 participants with painful DPN (P=0.03). Skin biopsy data revealed a significant positive correlation between sub-epidermal nerve density and vitamin D levels (P=0.01, r=0.42) indicating those with the lowest nerve fiber density had the lowest vitamin D levels. Researchers additionally found a significant negative correlation between vitamin D levels and pain scores; meaning people with the highest pain scores had the lowest serum vitamin D levels (P=0.02, r=-0.3).

Conclusion: The results demonstrated that patients with lower nerve fiber density had lower vitamin D levels. Clinically, those with painful DPN had the lowest vitamin D levels. Results may suggest a role for vitamin D supplementation in painful DPN compared with painless DPN as indicated by lower serum vitamin D levels.

Key Point: Additional research is needed to determine if supplementation with vitamin D helps improve the severity of painful DPN.

References:

1. Shillo P, Selvarajah D, Greig M, et al. Reduced vitamin D levels in painful diabetic peripheral neuropathy. Diabet Med. 2018;00:1-8. doi: 10.1111/dme.13798