Low vitamin D level is a risk factor for various late-onset CNS demyelinating disorders. We investigated whether vitamin D deficiency influences disease in twitcher mice (GALCtwi/twi; twi), a murine model of Krabbe disease (KD), an inherited disorder caused by galactocerebrosidase (GALC) deficiency that leads to psychosine accumulation, oligodendrocyte (OL) loss, and CNS demyelination. We found that the in situ 1,25-dihydroxyvitamin D3 level was reduced, with a parallel increase in the expression of inflammatory cytokines and vitamin D-catabolizing enzymes in the brains of KD and twi mice compared with age-matched controls. Pups maintained on milk from lactating heterozygous (GALCtwi/+) mothers that were fed a vitamin D3-supplemented diet until weaning and then fed a vitamin D3-supplemented diet demonstrated delayed body weight loss and development of disease in twi mice. This delayed the onset of tremors and locomotor disabilities that eventually impacted the life span of twi mice (50 ± 2 days). Accordingly, the expression of antioxidant enzymes was increased with delayed psychosine accumulation, lipid peroxidation, and inflammatory response that eventually protected CNS myelin and axonal integrity in twi mice. In vitro studies revealed that 1,25-dihydroxyvitamin D3 enhances antioxidant defenses in OLs deficient for GALC or incubated with psychosine. Together these data provide the first evidence that vitamin D deficiency affects disease development in twi mice and that vitamin D3 supplementation has the potential to improve the efficacy of KD therapeutics. © 2014 Wiley Periodicals, Inc.