Smokers who pick up the habit in their early teens may nearly triple their risk of developing multiple sclerosis (MS) later on, according to the first study to look at the relationship between early smoking and MS.

In MS, the immune system attacks the protective myelin sheath that surrounds nerve cells, causing fatigue, movement problems, loss of coordination, and many other symptoms, which typically first appear in a person's 20s, 30s or 40s.

Scientists first proposed in the early 1980s that the autoimmune disease could be triggered by some sort of early-life exposure, although this "mysterious factor" has not yet been identified, explained Dr. Joseph Finkelstein of Johns Hopkins University School of Medicine in Baltimore, the lead researcher on the study.

Because smoking has been linked to MS, he added, he and his colleagues decided to look at whether starting to smoke early in life could boost MS risk. In collaboration with the Veterans Affairs MS Center for Excellence in Baltimore, Finkelstein and his team looked at a nationally representative sample of 30,092 people participating in the 2002 National Health Interview Survey. The research team matched 87 patients with MS to 435 healthy individuals without the disease.

In the general population, the researchers found, 19.3 percent of people had started smoking before age 17, but 32.6 percent of the MS patients had started smoking early. After they accounted for gender, education and other factors that might influence both smoking and MS risk, they found that the early smokers were 2.7 times more likely than never-smokers to develop MS. But for people who started smoking at 17 or older, there was no increased MS risk.

For the many other known health effects of smoking, such as heart disease and chronic obstructive pulmonary disease, Finkelstein noted, both early and late smokers were equally at risk. But for MS, he added, the study "confirms this theory of early exposure."

Smoking is known to damage tissue, promote inflammation and injure the immune system, and this is likely how early smoking might predispose some people to developing MS, the researcher said.

The findings provide yet another reason for people to stay away from cigarettes, he added. "It's very important to continue public health campaigns or any other avenues to ensure that smoking eventually is eradicated."