To evaluate whether vitamin D is associated with multiple sclerosis (MS) status and disease severity in African Americans.

Serum 25-hydroxyvitamin D was compared in a cross-sectional sample of 339 African Americans with MS and 342 African American controls. Correlations between disease severity (Multiple Sclerosis Severity Score [MSSS]) and 25-hydroxyvitamin D levels were sought.

A total of 71% of controls and 77% of patients with MS were vitamin D deficient (<50 nmol/L; <20 ng/mL), and 93% of controls and 94% of patients with MS were vitamin D insufficient (<75 nmol/L; <30 ng/mL). Median unadjusted (29.7 vs 36.6 nmol/L, p = 0.0001) and deseasonalized (p = 0.0013) 25-hydroxyvitamin D levels were lower in the MS group. Multivariable analysis revealed that differences in latitude and ultraviolet index accounted for much of this association. The median (interquartile range) MSSS was 6.1 (4.8-8.1). There was no apparent association between the MSSS and vitamin D status. A greater proportion of European genetic ancestry, a measure of genetic admixture, was positively correlated with 25-hydroxyvitamin D (p = 0.007).

Levels of 25-hydroxyvitamin D were lower in African Americans with MS than controls, an observation primarily explained by differences in climate and geography. There was no apparent association between vitamin D status and disease severity. These results are consistent with observations in other populations that lower 25-hydroxyvitamin D is associated with having MS, but also highlight the importance of climate and ancestry in determining vitamin D status.