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Smokers who quit when they are young adults can live almost as long as people who never smoked, groundbreaking new research has found.

Smoking cuts at least 10 years off a person’s lifespan. But a comprehensive analysis of health and death records in the United States found that people who quit smoking before they turn 40 regain almost all of those lost years.

“Quitting smoking before age 40, and preferably well before 40, gives back almost all of the decade of lost life from continued smoking,” said Prabhat Jha, head of the Centre for Global Health Research at St. Michael’s Hospital and a professor in the Dalla Lana School of Public Health at the �ؿ�ζSM.

“That’s not to say, however, that it is safe to smoke until you are 40 and then stop,” said Jha. “Former smokers still have a greater risk of dying sooner than people who never smoked. But the risk is small compared to the huge risk for those who continue to smoke.”

His findings were published today in the New England Journal of Medicine.

Jha’s team found that people who quit smoking between ages 35 and 44 gained about nine years and those who quit between ages 45-54 and 55-64 gained six and four years of life, respectively.

The study is unique as it examines the risks of smoking and the benefits of stopping among a representative sample of Americans.  Earlier studies had examined specific groups such as nurses or volunteers who are healthier than average Americans overall.  Importantly, the study is among the first to document the generation of women who started smoking when they were young and kept smoking through their adult lives.

“Women who smoke like men, die like men,”Jha said. For women, the risks of dying from smoking-related causes are 50 per cent greater than found in the studies conducted in the 1980s.

Women and men who smoke both lost a decade of life. Current male or female smokers ages 25-79 had a mortality rate three times higher than people who had never smoked. Never smokers were about twice more likely to live to age 80 than were smokers.

This study adds to recent evidence from Britain, Japan and the United States that smoking risks involve about a decade of life lost worldwide. This includes a review of 50 years of smoking mortality in the United States published in the same issue of the New England Journal of Medicine and led by Dr. Michael J. Thun and other researchers from the American Cancer Society.

While about 40 million Americans and 4 million Canadians smoke, most of the world’s estimated 1.3 billion smokers live in low- and middle-income countries. Worldwide about 30 million young adults begin smoking each year (about half of all young men and 10 per cent of young women) and most do not stop.

In many high-income countries more than half of people who ever smoked have quit, cessation remains uncommon in most low- and middle-income people. On current trends, smoking will kill about 1 billion people in the 21st century as opposed to ‘only’ 100 million in the 20th century.

Professor Amartya Sen, the noted Harvard University economist who won the 1998 Nobel Prize in economics, said “the inability to develop an appropriate public policy about smoking has been one of the bigger failures of public action in India, China and most other developing countries, in contrast to strong tobacco control in most western countries.

“This study brings out how great the threat actually is, and shows that risks of death from smoking are even larger than previously thought,” said Professor Sen, who was not involved in the study.  “The result is of great global significance.”

Jha noted that smoking rates in the United States, China and India would decline much faster if their governments levied high taxes on tobacco, as seen in Canada and France. Taxation is the single most effective step to get adults to quit and to prevent children from starting, he said.

Jha’s research used data from the U.S. National Health Interview Survey in which a representative cross-section of the population is surveyed every year about a broad range of health topics. More than 200,000 survey participants were linked to the National Death Index, which includes death certificate information for all Americans since 1986.  The researchers related about deaths of about 16,000 people to their past reported smoking.

Jha advises various governments around the world on disease control strategies.  He is the principal investigator of the Million Death Study in India, one of the largest studies of premature deaths in the world.

The research was funded by the National Institutes of Health, the Canadian Institutes of Health Research and the Disease Control Priorities-3 project of the Bill and Melinda Gates Foundation.