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People who quit smoking see major gains in life expectancy after just a few years, researchers at Unity Health and the University of Toronto have found.

The study, , shows that smokers who quit smoking before age 40 can expect to live almost as long as those who never smoked. Those who quit at any age return close to never-smoker survival 10 years after quitting, and about half that benefit occurs within just three years.

“Quitting smoking is ridiculously effective in reducing the risk of death and people can reap those rewards remarkably quickly,” said Prabhat Jha, executive director of the Centre for Global Health Research at Unity Health Toronto and a professor at U of T’s Dalla Lana School of Public Health and Temerty Faculty of Medicine.

The observational study included 1.5 million adults in four countries (the U.S., U.K., Canada and Norway), followed over 15 years. Smokers between the ages of 40 and 79 had an almost three-fold risk of dying compared to those who never smoked, meaning on average they lost 12 to 13 years of life.

Former smokers lowered their risk of death to 1.3-fold (or 30 per cent higher) compared to never smokers. Stopping smoking at any age was associated with longer survival, and even those who quit for less than three years gained up to six years in life expectancy.

“Many people think it’s too late to quit smoking, especially in middle age,” said Jha. “But these results counter that line of thought. It’s never too late, the impact is fast and you can reduce risk across major diseases, meaning a longer and better quality of life.”

In particular, the researchers found that quitting smoking reduced the risk of dying from vascular disease and cancer. Former smokers also reduced their risk of death from respiratory disease, but slightly less so – likely due to residual lung damage.

There are currently about 60 million smokers in the four countries involved in the study and over a billion worldwide. The global rate of smoking has fallen by more than 25 per cent since 1990, but tobacco is still a leading cause of preventable death.

Jha said the findings should add urgency to efforts by governments to support people who want to stop smoking.

“Helping smokers quit is one of most effective ways to substantially improve health. And we know how to do that, by raising taxes on cigarettes and improving cessation supports.”

Canada is long overdue for an increase in the federal excise tax on cigarettes, and many other countries could lower smoking rates by raising taxes, Jha said. Cessation supports can include clinical guidelines and patient resources such as helplines, but also a whole-health-system approach.

“When smokers interact with the health-care system in any way, physicians and health professionals can encourage them to quit, pointing out how well quitting works,” Jha said. “This can be done with concern and without judgement or stigma, recognizing that cigarettes are engineered to be highly addictive.”

The research was supported by the Canadian Institutes of Health Research.