The news comes from a seven-year study of more than 123,000 European adults. Reported in BMJ Online First, it's the work of researchers including Paolo Vineis, a professor at Imperial College London.
Some of the adults had never smoked. The rest had quit cigarettes at least 10 years earlier. They were asked about their exposure to passive smoke as children and as adults.
During the study, 97 people were diagnosed with lung cancer. Twenty of those cases affected the mouth and throat regions. Chronic obstructive pulmonary disease and emphysemaChronic obstructive pulmonary disease and emphysema killed 14 participants.
A history of exposure to tobacco smoke was an important risk factor. Across the board, former smokers were more likely to have lung problems than lifelong nonsmokers. But that wasn't the only factor. Secondhand smoke also had a lingering legacy.
Childhood Smoke Exposure and Adult Cancer
Secondhand smoke bided its time. It didn't cause lung cancer right away. But over the years, it took its toll.
Childhood exposure to secondhand smoke raised lung cancer risk, even for people who never smoked. The more secondhand smoke a child breathed, the more likely he or she was to grow up to have lung cancer.
Kids who breathed secondhand smoke for many hours every day were 3.6 times more likely to have lung cancer when they became nonsmoking adults than those raised in smoke-free homes.
Smaller amounts of secondhand smoke were also damaging.
Children who had daily (but not constant) exposure were twice as likely to have lung cancer when they became nonsmoking adults. Those whose parents smoked a few times per week were 50% more likely to have lung cancer when they became adults, even though they themselves had never smoked.
Former Smokers More Vulnerable
The study also addressed adult exposure to secondhand smoke. Those cases focused on smoke in the workplace.
Former smokers fared worst. They were up to twice as likely to have lung problems when exposed to secondhand smoke as nonsmokers in similar conditions. The researchers say the reasons why aren't clear. Yet former smokers could have a higher susceptibility to diseases and cancer due to prior cell damage from past smoking.