There is "no clear link" between secondhand smoke and lung cancer, a study led by researchers at Stanford University has found.
After a decade-long study of more than 76,000 women, the researchers concluded that while there is still a strong association between smoking and lung cancer, there is no significant relationship between the cancer and exposure to passive smoke.
Published in the latest Journal of the National Cancer Institute, the study found that among current smokers, lung cancer was 13 times more common than in non-smokers, and four times more common among former smokers. But for women who had never smoked, it found that exposure to secondhand smoke did not significantly increase the risk of lung cancer.
Among the group of women who had lived with a smoker for 30 years or more, however, the study concluded that there was a relationship of "borderline statistical significance" between exposure to passive smoke and lung cancer.
Ange Wang, the Stanford University medical student who presented the study in June at this year's meeting of the American Society of Clinical Oncology in Chicago, said: "The fact that passive smoking may not be strongly associated with lung cancer points to a need to find other risk factors for the disease [in non-smokers]."
The findings of the study will likely be questioned by Cancer Research UK however, who state on their website that "second-hand smoke can increase a non-smoker's risk of getting lung cancer by a quarter, and may also increase the risk of cancers of the larynx (voice box) and pharynx (upper throat)."