A new study disputes the common belief that blacks have a lower risk of developing MS.
The incidence of multiple sclerosis is higher in black women than in white women, according to a Kaiser Permanente study published today in the journal Neurology. The findings are contrary to the widely accepted view that blacks are less susceptible to MS, according to the researchers.
Researchers examined the electronic health records of more than 3.5 million members of Kaiser Permanente Southern California between January 2008 and December 2011, and identified 496 people newly diagnosed with MS. Of those cases, black patients had a 47 percent higher risk of MS than white patients, while Hispanic and Asian patients had a 50 percent and 80 percent lower risk than white patients, respectively.
The study also found that 70 percent of MS cases occurred in women, but that also was more pronounced among black patients than white patients. In addition, black women had a higher incidence of MS than white patients of both genders; black men had a similar risk of being diagnosed with MS compared with white men. The lower risk among Hispanic and Asian patients was true for both sexes.
“Our findings do not support the widely held belief that blacks have a lower risk of MS than whites, but that MS risk is determined by complex interactions between race, ethnicity, sex, environmental factors and genotypes,” said study lead author Annette Langer-Gould, M.D., Ph.D., of the Kaiser Permanente Southern California Department of Research and Evaluation. “Although additional research is needed, possible explanations for the higher incidence of MS in black women include a greater prevalence of hormonal, genetic, or environmental risk factors such as smoking, compared to patients from other racial or ethnic groups.”
The study estimates that in the U.S., 19,000 people per year or 250 per week are newly diagnosed with MS, a chronic, often disabling disease that attacks the central nervous system. Symptoms may be mild, such as numbness in the limbs, or severe, such as paralysis or loss of vision. The progress, severity and specific symptoms of MS are unpredictable and vary in individual patients.
The National MS Society estimates that more than 2.1 million people are affected by MS worldwide. Because the Centers for Disease Control and Prevention does not require U.S. physicians to report new cases of MS and the symptoms can be vague, the prevalence of the disease in this country can only be estimated.
According to the researchers, the belief that MS is rare in blacks is based on worldwide prevalence studies and a single study of Korean War veterans in the 1950s, which found that white men were twice as likely as black men to receive disability compensation for MS.
“A possible explanation for our findings is that people with darker skin tones have lower vitamin D levels and therefore an increased risk of MS. However, this does not explain why Hispanics and Asians have a lower risk of MS than whites, or why only black women but not black men are at a higher risk of MS,” Dr. Langer-Gould said. “Our findings indicate that including persons from different racial and ethnic groups in future studies of MS susceptibility and prognosis will likely reveal important insights into the causes of this often debilitating disease.”