Multiple sclerosis, long considered a disease of white females, has affected more black women in recent years, a new study finds. Hispanic and Asian women, who have previously seemed to be at less risk of MS, remain so, researchers report May 7 in Neurology. The findings bolster a theory that vitamin D deficiency, which is common in people with dark skin in northern latitudes, contributes to MS.
MS is a debilitating condition in which the protective coatings on nerves in the central nervous system get damaged, resulting in a loss of motor control, muscle weakness, vision complications and other problems. The National Multiple Sclerosis Society estimates that 2.1 million people worldwide have the condition.
The researchers scanned medical information from 3.5 million people who were members of the health maintenance organization Kaiser Permanente Southern California and found that 496 people received diagnoses of MS from 2008 through 2010. Of these patients, women comprised 70 percent, not an unusual fraction for people with MS. Surprisingly, the patients included 84 black women. That means the annual incidence of MS in black women was 10.2 cases per 100,000 people. That’s not a great risk for an individual, but it was higher than the annual rates for white, Hispanic and Asian women, which were 6.9, 2.9 and 1.4 per 100,000 people, respectively.
Among blacks, women had three times the incidence as men; in the other racial and ethnic groups, the MS rate in women was roughly double that of men.
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“This study actually confirms what clinicians practicing in African-American areas have already suspected,” says study coauthor Annette Langer-Gould, a neurologist in Kaiser’s Department of Research and Evaluation in Pasadena, Calif. A 2012 study of military personnel found a similar trend, but the Kaiser database includes a broader cross-section of the population and wider age range, she points out.
“This is a good study, an important study,” says George Ebers, a neurologist at the University of Oxford in England. Ebers says other work suggests that MS is on the rise.
The cause of MS is unknown, but it is widely thought to be a combination of genetic predisposition and environmental factors. Langer-Gould says that women’s higher MS frequency might be related to hormones since the disease rarely strikes females before puberty or after menopause.
The two studies showing a relative rise in blacks getting diagnosed with MS raise the specter of vitamin D deficiency. MS could be linked to a lack of sunlight exposure, she says. It’s well established that many dark-skinned people living in North America and northern Europe have trouble maintaining adequate vitamin D levels in winter (SN: 7/16/2011, p. 22).
Obesity may play a role, too, Ebers says, since excess fatty tissue lowers vitamin D levels in the blood. “But there’s no single factor” that can explain why some people get MS and others don’t, he says. Smoking and exposure to Epstein-Barr virus, which in some people causes infectious mononucleosis, add to MS risk, he says. And the biggest long-term contributor might be overzealous cleanliness in a child’s early years. Citing the hygiene hypothesis (SN: 1/29/2011, p. 26; SN Online: 5/2/2013), Ebers notes that greater attention to hygiene in the West has coincided with the rise of MS and other immune-related conditions in recent decades.
In any case, he says, the new data suggest that multiple sclerosis is a moving target. “The MS rate in blacks has obviously changed.”