Multiple sclerosis (MS) is more common in black women than in white women, according a new study.

The research was conducted by Kaiser Permanente and was published in the journal Neurology. The results contradict the widely believed notion that black people are less vulnerable to the disease.

The electronic health records of over 3.5 million members of Kaiser Permanente Southern California were analyzed from the beginning of 2008 to the end 2011. A total of 496 patients newly diagnosed with MS were identified.

Of these new cases, black patients had a 47% greater likelihood of MS compared to white patients. Results also showed that Hispanics had a 50% reduced risk compared to white patients, and Asians had a 80% lower chance than whites.

Seventy percent of MS cases occurred among females, the researchers said. However, "this preponderance of females diagnosed was more pronounced among black patients than white patients."

Black females had an increased prevalence of multiple sclerosis compared to both white males and females, the authors pointed out. Black men, on the other hand, had a comparable probability of MS riskto white men.

Additionally, the reduced risk among Hispanic and Asian patients was true for both males and females.

Leading author Annette Langer-Gould, MD, PhD, of the Kaiser Permanente Southern California Department of Research & Evaluation, said:

"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.

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."

Approximately 19,000 Americans are diagnosed with MS each year, or 250 each week, according to the report. The mean age of MS diagnosis among the subjects was 41.6 years, however, onset can occur between 8.6 and 78.3 years.

Although the average time from the start of symptoms to MS diagnosis was 4 months, it could be as long as 40 years, the authors explained

Overall, Hispanic and Asian patients were younger at the time of their diagnosis than whites and African-Americans.

Worldwide prevalence reports as well as a single study of Korean War veterans in the 1950s, which showed that white males had a two times higher chance of receiving disability compensation for MS than blacks, are responsible for the idea that MS is not common in black people.

Dr. Langer-Gould concluded:

"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.

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."

What is Multiple Sclerosis?

According to the National MS Society, MS is a chronic, sometimes disabling disease that attacks the central nervous system, which includes the brain, spinal cord, and optic nerves.

The development, severity, and particular symptoms of MS are unforeseeable and differ from one patient to the next. Symptoms could be mild - numbness in the limbs - or severe - paralysis or loss of sight.

Over 2.1 million people around the world are affected by MS, according to estimates from the National MS Society.

The prevalence of MS among Americans can only be estimated, the authors explained, because the CDC (Centers for Disease Control and Prevention) does not ask doctors to report novel MS cases and symptoms can go unnoticed.

A previous study from October 2012 showed that marijuana extract can relieve symptoms of the disease.

A different report from March 2013 informed that the U.S. Food and Drug Administration (FDA) approved Tecfidera (dimethyl fumarate) capsules to treat adults with relapsing forms of MS.

Written by Sarah Glynn