smoking may boost teens' asthma risk

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NEW YORK, (Reuters) Teenagers who smoke are more likely than their peers to develop asthma, a finding that highlights the immediate danger of the habit, researchers reported.

Experts have suspected that smoking is a risk factor for asthma, but studies have been inconclusive.

One of the problems is that most studies have looked at adults.

It's difficult, for instance, to separate asthma symptoms from emphysema and chronic bronchitis, which are common in older smokers.

So for the current study, researchers at the University of Southern California in Los Angeles followed 2,609 children between the ages of eight and 15 who were initially asthma-free.

They found that kids who said they regularly smoked were four times more likely than non-smokers to develop asthma over the next eight years. Children whose mothers had smoked during pregnancy were particularly vulnerable.

The findings are among the first to show that some health consequences of smoking emerge quickly, the study authors report in the American Journal of Respiratory and Critical Care Medicine.

Unlike the case with heart disease and lung cancer, ''the risk of asthma is now,'' said Dr. Frank D. Gilliland, the study's lead author yesterday.

And that knowledge, he told Reuters Health, might persuade more teens to quit smoking or never start. ''This is an important public health message to get out,'' Gilliland said.

During the study, the adolescents completed yearly interviews and questionnaires on smoking habits and asthma symptoms. The four-fold higher risk of asthma persisted in the smokers, regardless of several other factors -- including race, family income and family history of asthma.

Children whose mothers had smoked during pregnancy were nearly nine-times more likely than non-smokers to develop asthma.

The finding, according to Gilliland's team, suggests that fetal exposure to tobacco smoke makes children's airways more susceptible to damage from active smoking.

A second study published in the same journal suggests that certain adults are especially vulnerable to the respiratory effects of secondhand smoke.

More than 1,600 adults who never smoked were followed for 11 years. Dr Margaret W Gerbase of University Hospitals of Geneva and colleagues found that those who were persistently exposed to secondhand smoke were more likely to develop a chronic cough.

But secondhand smoke was particularly troublesome for adults with bronchial hyperreactivity -- where the airways tend to constrict to a greater-than-normal degree in response to irritants.

They were more likely to report chronic breathing difficulty, and their lung function tended to decline over time.

These individuals, according to the study authors, may be at particular risk of chronic lung disease. But because many people with bronchial hyperreactivity wouldn't know it, Gerbase's group concludes, policies that protect everyone from secondhand smoke are the ''only way'' to go.