Smoking and Multiple Sclerosis Risk

Published on September 7, 2009 12:46 PM

An estimated 350,000 Americans suffer from MS. Older studies suggest that it affects about 1.1 million people worldwide. The incidence appears to be increasing in women.
Multiple sclerosis befalls worldwide but is most common in Caucasian people of northern European origin, especially those of Scottish descent. It is extremely rare among Asians, Africans, and Native Americans. Specific groups (e.g., gypsies, Eskimos, Bantus) have never reported a case.
As it is known, smoking cigarettes increases the risk of multiple sclerosis (MS), but recent Swedish study found that the substance that makes cigarettes addictive, nicotine, doesn't seem to be at fault.
While male smokers were 1.8 times as likely to have MS as non-smokers, and MS risk increased 1.4-fold for women who smoked, people who used Swedish snuff were actually less likely to have the disease, Dr. Anna K. Hedstrom of the Karolinska Institute and her colleagues found.
"It's not a healthy thing, it's better than smoking, but it still has negative effects in the long run," the researchers added.
Not only one study but eight out of nine studies investigating smoking and MS risk have found an increased probability of developing the disease among smokers. But only the last study looked at "cumulative dose," or how long and how much people smoked, and MS risk.
In the last study, researchers compared smoking and snuff use among 902 people diagnosed with MS and 1,855 healthy individuals drawn from the general population.
Fifty-seven percent of the MS patients reported being "ever-smokers" in the year before diagnosis, compared to 48 percent of controls at an equivalent point in time.
At the end of the investigation they found that "ever-smokers" were 1.5 times more likely to have MS than "never-smokers," while the risk was 1.6-fold greater for current smokers and 1.4 times greater for past smokers compared with never-smokers.
But for snuff users, risk of MS was 20 percent lower than it was for people who had never used any kind of tobacco.
Researchers concluded that the longer they'd used snuff, the lower their risk, and the longer a person smoked, the higher their risk.
Hedstrom noted that as far as any potential benefit of nicotine it's possible the chemical may have some protective effect on the nervous system. She added that some research has linked nicotine use to a reduced risk of Parkinson's disease.
It's not clear yet why cigarette smoking might encourage MS risk, although there are many theories, she said.