AILSA CHANG, HOST:

People who have smoked most of their lives may think it's too late to quit, but a new NIH-AARP study finds that even smokers over 60 can lengthen their lives if they kick the habit. Dr. Sarah Nash, the main author of the study, joins us today from Alaska Public Media in Anchorage. Thank you so much for speaking with us.

SARAH NASH: Thank you for having me.

CHANG: So how old were the smokers you studied, and when did they quit?

NASH: We looked at people who are aged over 70 years, and we looked at current smokers and people who had quit throughout the life course. So we had never-smokers. We had people who had quit in their 30s, 40s, all the way up to the 60s.

CHANG: And for the people who quit smoking in their 60s, how did you measure the benefit to their health? Was it just in terms of extra years that they lived?

NASH: So what we did is we compared the risk of dying among people who had quit in each decade of life and people who had never smoked to the risk of death in people who are still smoking in the 70s. So we basically compared the mortality among those groups.

CHANG: Right.

NASH: And what we found was that people who quit during the 60s had a lower risk of death than people who continued to smoke into their 70s.

CHANG: What about benefits of quitting on things like preventing smoke-related diseases, like heart disease or lung cancer?

NASH: Well, we know that there's definitely a benefit to those diseases from smoking, so what we were looking at was deaths from those diseases. So we actually looked at mortality from a whole bunch of different causes. We looked at death from lung cancer, death from other smoking-related cancers, death from respiratory infection, death from heart disease and death from stroke.

CHANG: And found that the mortality rates were lower for people who quit in their 60s compared to those who quit in their 70s or 80s.

NASH: Exactly.

CHANG: But I would assume the earlier you quit smoking, the better for your health, right? Like, what did you find on that point?

NASH: That's exactly what we found. So we found that the risk of death, obviously, was lower in people who had quit earlier in life. But what was really surprising to us was that even the people, as you say, who had quit during the 60s - it was 23 percent less likely to die during the study than those who continued to smoke. So that's a fairly substantial reduction in mortality risk.

CHANG: I feel like I meet a lot of smokers who - you know, who have counter examples to a study like this in their head. Like, well, I knew Joe so and so, and he never quit smoking, and he lived till he was 93 years old. How do you control for things like genetics?

NASH: So I think we all know some of those people are, right? But I think the important thing is that we're looking at - rather than just taking an anecdote in one person, we're looking at this - we looked at this in 160,000 people.

CHANG: Did you factor in how much, how often the subjects smoked?

NASH: Yes, we did. What we do is we calculate what we call pack years? It's the cumulative exposure over the life course, and that was one of the factors that we adjusted for in our analysis.

CHANG: Did anything surprise you about these findings in the study?

NASH: So we know the risk of mortality is lower among those who quit smoking, so that in itself wasn't surprising.

CHANG: Right.

NASH: But the magnitude of the observed benefit of quitting in one's 60s - that that was remarkable, I think.

CHANG: Dr. Sarah Nash was co-author of a study published in the American Journal of Preventive Medicine. Thank you so much for joining us, Sarah.

NASH: Thank you for having me. Transcript provided by NPR, Copyright NPR.