Narrator: This is Science Today. Researchers at the University of California, San Francisco say there's a crucial link between the age a person starts smoking and how much DNA damage is present in their lungs. Epidemiologist John Wiencke explains.
Weincke: Our evidence strongly indicates that if a person starts smoking very early in life, before adolescence, the damage that accumulates persists much longer than if a person starts smoking, say when they're 20 years or so. It may actually take many years for it to clear out of the lungs and of course, once mutations are induced, theoretically, they're around forever.
Narrator: Many lung cancer patients studied began smoking before age ten.
Weincke: It's always been controversial about whether when you start smoking is an independent risk factor for lung cancer as opposed to how much you smoke, because people that start smoking very early in life tend to smoke more cigarettes per day and they tend to be heavier smokers, so there's this confounding with age and how much you smoke.
Narrator: For Science Today, I'm Larissa Branin.