Jan. 30 (HealthDay News) -- Exposure to secondhand smoke worsens lung function in people with cystic fibrosis (CF), especially those with certain genetic variations, say U.S. researchers.

"Despite public health warnings, including a recent U.S. surgeon general's report stating that there is no risk-free level of secondhand smoke exposure, substantial numbers of individuals with CF are exposed to secondhand smoke. Unfortunately, published studies have been inconsistent in associating poorer clinical outcomes in patients with CF with secondhand smoke exposure," the Johns Hopkins University researchers wrote.

The researchers looked at several areas involving secondhand smoke and CF, a fatal disorder that affects more than 30,000 people in the United States. They analyzed data on hundreds of CF patients, and found that secondhand smoke exposure was associated with decreases in all measures of lung function studied. Socioeconomic status did not worsen the relationship between secondhand smoke and reduced lung function.

The researchers also found that certain mutations in the CF-causing gene (CFTR) determine the degree of effect that secondhand smoke has on lung function in CF patients.

The study is published in the Jan. 30 issue of the Journal of the American Medical Association.

"CF may be a good model for uncovering gene-environment interactions that are detrimental to lung function. This study also raises the specter that healthy children bearing certain genetic variants may be at much higher risk for worse outcomes as a result of secondhand smoke exposure," the study authors wrote.

"Demonstration that genetically defined subsets of patients with CF exposed to secondhand smoke in the home have a substantial lifetime reduction in lung function provides potent justification for eradication of cigarette smoke exposure for all individuals with this life-limiting disorder," they concluded.

SOURCE: Journal of the American Medical Association, news release, Jan. 29, 2008