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 these diagnosed 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 compared to white patients, respectively.
The study also found that 70 percent of MS cases occurred in females, but this preponderance of females diagnosed 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, while black men had a similar risk of being diagnosed with MS compared to 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, MD, PhD, of the Kaiser Permanente Southern California Department of Research & 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 19,000 people per year — or 250 per week — are newly diagnosed with MS in the U.S. The researchers identified the average age of MS diagnosis as 41.6 years, but found onset occurred anywhere between 8.6 and 78.3 years among the study participants. The study also found the median time from symptom onset to MS diagnosis was four months, but could be as long as 40 years. Hispanic and Asian patients were generally younger at the time of MS diagnosis than white and black patients.
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 white men were twice as likely to receive disability compensation for MS as black men.
"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," said Dr. Langer-Gould. "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."
The National MS Society defines MS as a chronic, often disabling disease that attacks the central nervous system, which is made up of the brain, spinal cord and optic nerves. 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 from one person to another. The organization 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 symptoms can be invisible, the prevalence of MS in the U.S. can only be estimated.