Black women have a higher incidence of multiple sclerosis than white women

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Multiple sclerosis is more common in black women than in white women, according to a Kaiser Permanente, Oakland, USA, study published in Neurology. The findings run contrary to the widely accepted belief that black people are less susceptible to multiple sclerosis, according to the authors of the study.

The authors 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 multiple sclerosis. Of the diagnosed cases, black patients had a 47% higher risk of multiple sclerosis than white patients. Hispanic and Asian patients had a 50% and 80% lower risk compared to white patients, respectively.

In the study it was also found that 70% of multiple sclerosis cases occurred in females, but the preponderance of females diagnosed was more pronounced among black patients than white patients. In addition, black women had a higher incidence of multiple sclerosis than white patients of both genders, while black men had a similar risk of being diagnosed with the disease 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 black patients have a lower risk of multiple sclerosis than white patients, but that multiple sclerosis risk is determined by complex interactions between race, ethnicity, sex, environmental factors and genotypes,” said study lead author Annette Langer-Gould, of the Kaiser Permanente Southern California Department of Research and Evaluation, USA. “Although additional research is needed, possible explanations for the higher incidence of multiple sclerosis 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 estimated that 19,000 people per year—250 people per week—are newly diagnosed with multiple sclerosis in the USA. The researchers identified the average age of multiple sclerosis 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 multiple sclerosis diagnosis was four months, but could be as long as 40 years. Hispanic and Asian patients were generally younger at the time of multiple sclerosis diagnosis than white and black patients.

According to the researchers, the belief that multiple sclerosis 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 multiple sclerosis 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 multiple sclerosis. However, this does not explain why Hispanic patients and Asian patients have a lower risk of multiple sclerosis than white patients, or why only black women but not black men are at a higher risk of multiple sclerosis,” said Langer-Gould. “Our findings indicate that including persons from different racial and ethnic groups in future studies of multiple sclerosis susceptibility and prognosis will likely reveal important insights into the causes of this often debilitating disease.”

This study is part of Kaiser Permanente’s ongoing investigations into diverse and representative member population as a way to better understand multiple sclerosis, according to a press release. In January, a Kaiser Permanente study, also published in Neurology, found obesity in teenage girls was associated with an increased risk of developing multiple sclerosis. Researchers are also currently recruiting patients for the MS Sunshine Study to examine the complex interactions between multiple sclerosis risk factors such as sunshine, low vitamin D, skin tone, infections, other environmental and genetic factors across racial/ethnic groups. Researchers expect to release findings of this study in 2015.