Exposure to second hand smoke seems to worsen lung function in people living with cystic fibrosis, especially in those with certain genetic variations, a team of U.S. researchers revealed.

"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 study says.

Cystic fibrosis is an inherited chronic disease that affects the lungs and digestive system of about 30,000 children and adults in the United States, according to the Cystic Fibrosis Foundation. If you are a non-smoker, exposure to second-hand smoke increases your risk of developing either lung cancer or heart disease by 20 percent.

Researchers at Johns Hopkins University School of Medicine in Baltimore studied 812 people averaged 19.5 with the disease and their exposure to second hand smoke. About 188 of them were exposed to second-hand cigarette smoke at home on regular basis. The study discovered that the lung function of those exposed to secondhand smoke was reduced by about 10 percent compared to those not exposed.

“It’s always been suspected that secondhand smoke is detrimental to lung disease patients and now we have a handle on one specific gene that clearly makes it worse for those with cystic fibrosis,” co-author of the study Garry Cutting wrote.

Second-hand smoke in a vehicle can be 23 times more toxic than in a house because of the smaller space.  Rolling down the window does not significantly decrease your exposure to second-hand smoke.

The researchers also looked at lung function in people who also had a specific version of a gene called TGFbeta 1 that affects the severity of this disease and asthma. They found that having this gene variant doubled the negative effects of second-hand smoke on lung function.

The researchers did not include in their study people with cystic fibrosis who are active smokers, but reports showed that “it’s absolutely disastrous for them to actively smoke,” Cutting said in a telephone interview with Reuters.

The researchers also pointed towards the complete “eradication of cigarette smoke exposure for all individuals with this life-limiting disorder,” following this findings.

The study, supported by a grant from the National Heart, Lung and Blood Institute, by the Flight Attendant Medical Research Institute, and by Cystic Fibrosis Foundation funding to Dr. Cutting and one of his co-authors, J. Michael Collaco, M.D., was published in the January 30 issue of the Journal of the American Medical Association.