| Sumario: | Individuals with spinal cord injury (SCI) are at increased risk for insufficient 25(OH)D levels and associated adverse health outcomes, highlighting the need for vitamin D supplementation. However, the optimal dosing strategy for vitamin D supplementation in this population remains unclear. To evaluate the efficacy of medium-dose (MD) and high-dose (HD) vitamin D3 supplementation in raising 25(OH)D levels above the sufficiency threshold of 75 nmol/L in individuals with SCI. A 12-month randomized, double-blind, placebo-controlled, superiority clinical trial was conducted in 42 individuals living with SCI for at least 3 years and who had insufficient 25(OH)D levels at baseline. Participants (7 female, 35 male; age 48 ± 10 years; 32 with paraplegia, 10 with tetraplegia) were randomly assigned to the placebo, MD intervention (24,000 IU D3 once every 4 weeks), or HD intervention (24,000 IU D3 once every 2 weeks) group. Baseline 25(OH)D levels (43 ± 16 nmol/L) did not differ between intervention groups (P =.8). Supplementation was well tolerated, and 25(OH)D levels remained well below the excess threshold. A dose-response effect on 25(OH)D levels was observed [F(2, 40) = 8.21, P <.001]. In the HD group, 46% of the participants reached sufficient levels. Participants having an incomplete lesion, higher baseline 25(OH)D levels, lower body mass index, supplementation during summer, autumn, or winter, or higher sun scores were more likely to reach sufficient 25(OH)D levels. Vitamin D3 supplementation effectively increased 25(OH)D concentration to sufficient levels in participants with specific characteristics. Higher supplementation doses are needed to successfully increase 25(OH)D levels in all individuals with chronic SCI.
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