Smoking cuts at least 10 years off lifespan but quitting before age 40 regains most of that time, a large new study suggests.

Canadian, American and British researchers analyzed smoking histories and death records for 113,752 women and 88,496 men in the U.S. over seven years.

"Those that quit by age 40 avoid about 90 per cent of the risk of continuing to smoke," said study author Dr. Prabhat Jha, head of the Centre for Global Health Research at St. Michael’s Hospital in Toronto.

"Those that quit by 30 are close to never smoker death rates," after considering their risks of heart attack, stroke, and lung and other cancers.

The message is that it's never too late to quit, he said.

But the researchers cautioned it is not safe to smoke until 40 and then stop because the risk is still substantial compared with those who never smoked and had similar levels of education, body fat and alcohol use.

Women who smoke like men die like men, researchers say. (Jonathan Alcorn/Reuters)

Dr. Graham Berlyne, a respirologist and chief of medicine at St. Joseph's Health Centre in Toronto, called the study important for its size that likely reflects the wider U.S. and Canadian population, and for its focus on the first generation of women who started smoking when they were young and continued through their adult lives.

"The years of smoking are not erased but the damage done is halted and the lungs have a huge capacity so that we can still function even having lost some capacity," Berlyne said.

Tracy Hager, 39, of Toronto, is using nicotine patches and lozenges to quit. She hasn't lit up in six weeks but her two teenagers have started.

"I was so disappointed, but I can't really blame anybody else but myself," said Hager, who is using the study's findings as further motivation.

Previous studies drew similar conclusions. The researchers noted evidence emerging from China and India points to a similar trend in declining life expectancy for smokers. In most high-income countries, there are more former smokers than current smokers, but that's not the case in low- and middle-income countries.

They called for higher prices for cigarettes through excise taxes, restrictions on smoking in public places, bans on tobacco advertising and promotion, and easy access to cessation efforts.

The study was funded by U.S. National Institutes of Health, the Canadian Institutes of Health Research and the Bill and Melinda Gates Foundation.

With files from CBC's Kim Brunhuber