Those lacking this capability and exposed to secondhand smoke may have a four-fold increased risk of lung cancer.

Researchers at The University of Texas M. D. Anderson Cancer Center in Houston say that compared with nonsmokers whose DNA repair capacity is considered normal -- nonsmokers with less efficient DNA repair capacity are almost twice as likely to develop lung cancer.

The study found participants showing the lowest ability to repair their DNA had a more than a three-fold increased risk of developing lung cancer.

"Our findings demonstrate that suboptimal DNA repair capacity together with secondhand smoke exposure are strong lung cancer risk factors in lifetime never smokers," study lead author Olga Gorlova said in a statement.

DNA repair capacity may be affected by genetics. First-degree relatives of those with lowest DNA repair capacity were 2.5 times more likely to develop lung cancer than were first-degree relatives of people with efficient DNA repair capacity.

The study is published in the journal Cancer Epidemiology, Biomarkers and Prevention.