VANCOUVER - A study published Thursday found smokers who quit when they are young adults can significantly reduce their risks of dying sooner.

"Quitting smoking before age 40, and preferably well before 40, gives back almost all of the decade of lost life from continued smoking," ?said the study's lead author Dr Prabhat Jha.

However, Dr Jha, who is also the head of the Centre for Global Health Research at St Michael's Hospital in Canada, said that does not mean it is safe to smoke until one turns 40 and then stop.

"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," he said.

Dr Jha's team obtained smoking and smoking-cessation histories from more than 200,000 people who were interviewed between 1997 and 2004 in the US National Health Interview Survey, and related these data to the causes of deaths that occurred by the end of 2006.

They found 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.

According to the researchers, about 30 million young adults begin smoking each year worldwide and most do not stop. On current trends, smoking will kill about 1 billion people in the 21st century as opposed to 100 million in the 20th century.

Dr Jha noted that smoking rates in the United States, China and India would decline much faster if those 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 added.

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