There's still more to learn about the risks of smoking and the benefits of quitting.
Studies in this week's New England Journal of Medicine show that the risk for women has been under-appreciated for decades. New data also quantify the surprising payoffs of smoking cessation especially under the age of 40.
Dr. Prabhat Jha of St. Michael's Hospital in Toronto, an author of one study, says before now it hasn't been possible to gauge female smokers' true risks. Not enough women had been smoking long enough.
"The group of women that started smoking seriously in and around 1960 can be followed up only now fully five decades later to understand what are the full consequences of smoking among women," Jha tells Shots.
In the 1980s, it looked like women who smoked were about 13 times more likely to die from lung cancer than women who never did. But one new analysis finds that female smokers are more than 26 times more likely to die of lung cancer than nonsmoking women twice the rate calculated 30 years ago.
And women's risk of death from any cause is 50 percent higher than previously thought.
The new data also quantify more precisely than ever the terrible costs of smoking for all smokers.
"What we found in studying over 220,000 adult Americans is that smoking leads to the loss of about a decade of life," Jha says.
Long-term smoking also reduces by half a smoker's chances of living to the age of 80.
But Jha says there are also bigger benefits from quitting than most people thought. A long-term smoker who quits before age 40 actually turns back the clock on his risk of dying gaining back nine out of the 10 years of life he'd have lost if he hadn't stopped.
"It's a very encouraging message," Jha says. "If you think about the average 45-year-old smoker in the United States, they probably started when they were age 15. They might be smoking for a quarter of a century. And they might think, 'Oh, it's too late. There's no point for me to quit because the damage is done.' But that's not true."
Dr. Michael Eriksen of Georgia State University, a longtime researcher on smoking and health, says looking at it this way might motivate more people to quit because they can relate it to their own lives.
"They're not stupid," Eriksen tells Shots. "They want a full life. They want to enjoy their grandchildren, their retirement. And realizing their life may be shortened by a full decade puts the risk in clear and stark terms."
Dr. Nancy Rigotti, who runs smoking cessation programs at Massachusetts General Hospital, agrees it might be more effective to emphasize what people have to gain if they stop smoking.
"The positive is a much better, more positive message," she tells Shots, "much more persuasive."
But she worries that some may interpret the message as saying it's OK to smoke until their 30s or even age 40, because if they quit then, they can reverse all or most of the damage.
"A lot of young women think, 'I can smoke until I get pregnant,' and people say, 'I can smoke until I'm 40.' But it's certainly easier to quit earlier rather than later," Rigotti says.
Rigotti says she'll start using the new findings right away in her everyday practice.
"I'm going to tell my patients that quitting is really important," she says, "they should be thinking about it now, but also that it's never too late to quit."
She also says the new information will come in handy as new Affordable Care Act provisions will require all health insurers to start covering smoking-cessation programs.