A new study shows that smoking may increase the risk of multiple sclerosis (MS) in people who also have specific established risk factors for multiple sclerosis. The research is found in the April 7, 2010, online issue of Neurology®, the medical journal of the American Academy of Neurology.
The research involved 442 people with multiple sclerosis and 865 people without the disease from 3 studies: the Nurses' Health Study I/Nurses' Health Study II, the Tasmanian MS Study, and the Swedish MS Study. Researchers first determined whether participants had known risk factors for multiple sclerosis, including having a high level of antibody in the blood to the Epstein-Barr virus (a common herpes virus that infects most people but is associated with multiple sclerosis in a small fraction of those infected), or having an immune-system-related gene called the HLA-DR15 gene (which is present in 20% of the population at large but 60% of patients with multiple sclerosis).
The study found that among those with high levels of the antibody to the Epstein-Barr virus, smokers were twice as likely to have multiple sclerosis as those who had never smoked. The same association was not seen in those with low antibody levels. The risk of multiple sclerosis associated with smoking was not different in people with and without the HLA-DR15 gene.
"The consistency of an association between MS, smoking, and the body's immune response to the Epstein-Barr virus based on these 3 distinct, geographically diverse studies suggests this finding is not due to chance," said study author Claire Simon ScD, with Harvard School of Public Health in Boston. "This relationship may provide clues as to why certain individuals develop MS while others do not."
In the United States, the average lifetime risk of developing multiple sclerosis is approximately 1 in 200 for women and 1 in 600 for men. Among those with high antibody levels to the Epstein-Barr virus, smokers may have up to a 2-fold increase in multiple sclerosis risk compared to nonsmokers.
Multiple sclerosis is the most common nontraumatic disabling neurologic disease in the United States.
The study was supported by the National Institutes of Health, the National Health and Research Council of Australia, the Australian Rotary Health Research Fund, and MS Australia.
Source: News Release
American Academy of Neurology
April 7, 2010