Effectiveness of a vitamin D regimen in deficient multiple myeloma patients and its effect on peripheral neuropathy.

PURPOSE: Peripheral neuropathy (PN) is common in multiple myeloma (MM) patients. More insight has been gained concerning the role of vitamin D in preventing PN. However, studies evaluating the effects of vitamin D3 supplementation on PN are lacking. The aims of this study are to (1) evaluate the effectiveness of a vitamin D3 regimen on achieving adequate vitamin D levels in deficient MM patients and to (2) exploratively evaluate the effect of vitamin D3 supplementation on PN. METHODS: Thirty-nine MM patients with inadequate (< 75 nmol/L [= 30 ng/mL]) 25-hydroxyvitamin D (25(OH)D) levels were included in this multicenter, prospective, single-arm study, of whom 35 patients completed the study. They received oral vitamin D3 for 6 months according to a dose escalation regimen that consisted of one or two loading doses of 200,000 international units (IU), and maintenance doses of 800, 1600, or 3200 IU/day depending on the 25(OH)D level. A validated questionnaire was used to measure PN. RESULTS: Median 25(OH)D increased from 38 (IQR 32-52) nmol/L at baseline to 77 (IQR 72-87) nmol/L after 6 months (P < 0.001). Adequate 25(OH)D levels were achieved by 66% of the subjects, and 34% were within the range of 50-75 nmol/L. Furthermore, in 37% of the participants, PN severity decreased (P = 0.007). CONCLUSION: The use of substantially higher vitamin D3 doses than recommended in current guidelines resulted in a significant increase in vitamin D levels in MM patients. Furthermore, evaluation of PN showed a significant decrease in PN grading. However, this exploratory evaluation needs further confirmatory research.