A recent study published in the online issue of Neurology shows that smoking increases the risk of multiple sclerosis (MS) in people who carry certain established risk factors for the disease.
The research took in 442 people with MS and 865 people without the disease from 3 studies - the Nurses' Health Study I and II, the Tasmanian MS Study and the Swedish MS Study.
The scientists first assessed whether participants had known risk factors for MS that include high level of antibody to Epstein-Barr virus in their blood or having a HLA-DR15 gene.
Epstein-Barr virus is a common herpes virus that can be contracted by most people but it is also observed to be related to a small number of MS patients. The HLA-DR15 gene is present in 20 per cent of the human population, but the percentage in MS patients is as high as 60 per cent.
The results of the study showed that in the category of participants who had high levels of the antibody to the Epstein-Barr virus, smokers were twice as likely to develop MS compared to those who had never smoked.
However, similar correlation was not observed in participants with low antibody level to the virus. Among participants with or without the HLA-DL15 gene, the risk of MS associated with smoking was not significant.
The author of the study, Claire Simon from the Harvard School of Public Health, in Boston said the results of the study were suggestive that it was not due to chance.
The consistency of an association between MS, smoking, and the body's immune response to the Epstein-Bar virus based on these three distinct geographically diverse studies suggests this finding is not due to chance, said Claire Simon.
This relationship may provide clues as to why certain individuals develop MS while others do not.