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Smokers who quit in their 40s or 50s can still reclaim many of the years that would otherwise be lost.

Smoking cuts more than a decade from life expectancy, but there is reason to have hope: Smokers who quit in their 40s or 50s can still reclaim many of the years that would otherwise be lost.

The findings, published on Wednesday in the New England Journal of Medicine, show that people who kick the habit by the age of 40 reduce their risk of smoking-related death by 90 per cent, giving them a near-normal life expectancy. People who stopped smoking at 45 to 54 years old gained about six years of life, compared with those who continued smoking, while those who quit at 55 to 64 gained about four years of life, the study found.

Quit smoking by the age of 30 and life expectancy will be identical to people who have never smoked.

"Many smokers would think, 'I've been smoking for 20 to 30 years and there's no point in me quitting,' but that's not true," said Dr. Prabhat Jha, head of the Centre for Global Health Research at St. Michael's Hospital in Toronto, who led the study. "Quitting is effective pretty much at any age."

That is not to say it is safe to take up the habit. Jha warns against interpreting the findings as a green light to smoke for a number of years before attempting to quit. Although the risks of smoking-related death are lower for people who quit in their 40s and 50s, they still face a higher risk of developing serious health problems, including lung cancer, heart attack, stroke and respiratory illness, compared with those who never smoked. There is "still some leftover damage from being an ex-smoker," Jha said.

The study is valuable on a number of fronts. It is quite large and is based on a representative sample of the U.S. population, which means that the results are likely applicable on a wide scale. More than 113,000 women and 88,000 men 25 and older were included in the study. Researchers examined smoking histories and data about the deaths of individuals in the cohort to make their conclusions.

The study is also one of only a handful that has been able to examine the long-term impact of smoking on the health of women because until the 1960s, the majority of women in countries such as the United States and Canada did not smoke. Now, decades later, researchers such as Jha have the opportunity to look at female smokers in depth.

What scientists have found is that smoking-related mortality is similar, regardless of gender. "Women who smoke like men die like men," Jha said.

The damage from failing to quit is unquestionable. Jha's new study shows that a lifetime of smoking reduces life expectancy by at least a decade. He added that only a minority of smokers reach the age of 80.

Tobacco is responsible for 37,000 deaths in Canada each year, according to the Canadian Lung Association.

"If you don't smoke, you're going to live a longer life," said Margaret Bernhardt-Lowdon, tobacco-issues spokeswoman for the association. "It really makes it very clear when they're talking about having a 10-year less life expectancy."

The association was not involved with the study, which was funded by grants from the U.S. National Institutes of Health Fogarty International Center, the Canadian Institutes of Health Research, the Disease Control Priorities Project and the Bill and Melinda Gates Foundation.

Smoking rates in Canada have come down drastically in recent decades. But in the past few years, the numbers have barely budged. About 17 per cent of Canadians 15 and older smoked in 2011, the same as in 2010. The number of smokers only fell 2 per cent in the five years prior to 2011, which is a much smaller decrease than in previous years.

The Canadian Cancer Society says on its website that the slowdown in progress is the result of the growing availability of contraband cigarettes.

Jha agrees that clamping down on contraband tobacco should be a priority in Canada. But he advocates for another price increase to deter smoking. When cigarette prices were raised in the 1990s, it did more to reduce smoking rates than any other public-health initiative, he said.

"You can really save a huge amount of lives in Canada from very simple things," Jha said.