A study shows that smoking may increase the risk of multiple sclerosis in people who also have specific established risk factors for multiple sclerosis.
The research involved 442 people with multiple sclerosis and 865 people without the disease from three studies: the Nurses’ Health Study I/Nurses’ Health Study II, the Tasmanian multiple sclerosis Study and the Swedish multiple sclerosis 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 multiple sclerosis, smoking and the body’s immune response to the Epstein-Barr virus based on these three distinct, geographically diverse studies suggests this finding is not due to chance,” said study author Claire Simon. “This relationship may provide clues as to why certain individuals develop multiple sclerosis while others do not.”
In the United States, the average lifetime risk of developing multiple sclerosis is approximately one in 200 for women and one in 600 for men. Among those with high antibody levels to the Epstein-barr virus, smokers may have up to a twofold increase in multiple sclerosis risk compared to non-smokers.
Multiple sclerosis is the most common non?traumatic disabling neurologic disease in the US among young adults.
References:
1. K. C. Simon, et al. Combined effects of smoking, anti-EBNA antibodies, and HLA-DRB1*1501 on multiple sclerosis risk. Neurology, April 7, 2010. doi:10.1212/WNL.0b013e3181dad57e
