Vitamin D Levels Linked to MS in African Americans

Pauline Anderson

May 27, 2011

May 27, 2011 — The link between low vitamin D levels and multiple sclerosis (MS) holds true for African Americans and white populations, a new study shows.

The largest study of its kind to date shows that levels of 25-hydroxyvitamin D were lower in African Americans with MS compared with controls, with much, although not all, of the association explained by differences in climate and geography.

The study, performed by J.M. Gelfand, MD, and colleagues at the University of California at San Francisco, also found that having more European genetic ancestry was correlated with vitamin D status but found no association between vitamin D status and MS severity.

The study appears in the May 24 issue of Neurology.

Vitamin D Deficiency

The aim of the study was to determine whether vitamin D status in black Americans is associated with having MS and whether lower vitamin D status correlates with MS disease severity.

Researchers used data from the African American Multiple Sclerosis Genetics Project, a study of self-identified African Americans with MS and unaffected African American controls, to select 339 MS cases and 342 controls for the study.

From blood samples, researchers measured the proportion of subjects with European genetic ancestry. They looked at seasonal variation and geographic location at the time that blood was drawn. As well, they analyzed the association between vitamin D status and disease severity using the Multiple Sclerosis Severity Score (MSSS) in the MS group.

The study found that the median unadjusted 25-hydroxyvitamin D level was significantly higher in the MS group vs control subject. In the MS group, more MS patients had 25-hydroxyvitamin D levels in a range considered vitamin D deficient (<50 nmol/L) compared with controls, but there was no difference between groups in those deemed vitamin D insufficient (<75 nmol/L).

Table. Vitamin D Levels in MS vs Control Subjects

Measure MS Group Control Group P
Median unadjusted 25-hydroxyvitamin D level, nmol/L 29.7 36.6 .0001
Vitamin D deficient, % 77 71 .074
Vitamin D insufficient, % 94 93 .78

MS = multiple sclerosis

The proportion of those considered vitamin D insufficient or deficient was very high in both groups though, they note. "This degree of vitamin D insufficiency may have important implications for bone health, cardiovascular, inflammatory, and neoplastic disease, in addition to its possible role in modulating MS," commented the study authors.

The cross-sectional design of the study did not allow for a determination of causality or of the relative contributions of UV radiation and vitamin D status. "Longitudinal studies with larger samples of African Americans will be needed to establish cause-effect relationships between vitamin D status and MS in this population," the study authors write.

The vitamin D association with MS was weakened, but was still present, after controlling for differences in climate and geography.

European Ancestry

European genetic ancestry was correlated with 25-hydroxyvitamin D status, even after adjusting for different latitudes.

"The proportion of European genetic ancestry was one of the stronger predictors of vitamin D status (but not MS status) in this African American study population," write the study authors. This correlation might simply reflect unmeasured differences in skin pigmentation, but genetically influenced differences in vitamin D use can't be excluded, they said.

The study illustrates why it might be wise not to rely on racial classification alone in determining the role of vitamin D, added the study authors. "This observation highlights the potential importance of controlling for genetic admixture in future studies of vitamin D in addition to, or in place of, race."

There was no association between low (≤6) vs high (>6) MSSS and vitamin D status. This could be due to a limited sample size, smaller effect sizes in darker pigmented people, or the use of the MSSS instead of relapse rate as a marker of disease, said the study authors. "It is also possible that the biological consequences of a lower vitamin D status in darker pigmented populations might be different than in lighter pigmented populations."

Studies show that African Americans have a lower vitamin D status than non-Hispanic whites and Mexican Americans probably because of melanin, the primary determinant of skin pigmentation. MS is less prevalent in African Americans than whites, but the disease course tends to be more severe.

The study was supported by the American Academy of Neurology Foundation/National Multiple Sclerosis Society Clinician-Scientist Development Award, the National Institutes of Health (NIH), the National Multiple Sclerosis Society and a University of California San Francisco (UCSF) Resident Research grant. Dr. Gelfand receives research support from the NIH and a UCSF CTSI Resident Research Grant, and his wife is an editorial team member of Neurology. For conflict information on other authors, see the original paper.

Neurology. 2011;76:1824-1830.

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