The largest and longest international study looking at the consequences of cigarette smoking concludes that those who quit dramatically reduce their risk of dying in middle age. The authors of the 25-year study also found some benefit for long time smokers who quit.
According to the World Health Organization, smoking is the major preventable cause of death among adults, claiming about 5 million lives globally each year.
About half of the deaths occur in people under the age of 70, with 13 percent of those between the ages of 30 and 60, mostly from cancer or heart disease.
What's not really been known is the risk of dying prematurely, particularly in middle age, as a result of smoking. In the largest study of its kind to date, Norwegian researchers followed 50,000 rural men and women born between 1925 and 1941.
The participants were divided into two groups that included smokers and non-smokers. Both groups were surveyed and underwent physical examinations in 1974, and the volunteers were periodically questioned about their smoking habits.
By the end of the study in 2000, 7,000 participants who had been between of 35 to 49 years old when the study began, had died.
"The key finding is that cigarette smokers are much more likely to die in middle age compared to people who have never smoked or compared to people who have smoked and have quit," said Ron Davis, a preventive medicine physician at the Henry Ford Health System in Detroit, Michigan.
Writing in the journal Annals of Internal Medicine, the authors report that 41 percent of men who smoked two or more packs of cigarettes a day during middle age died of lung cancer compared to 14 percent of non-smoking men.
Twenty-six percent of women who were heavy smokers developed lung cancer compared to only nine percent of non-smoking women. Cigarette smoking is considered the leading risk factor for lung cancer.
The Norwegian researchers found that mortalities related to cigarette smoking from any cause, including heart disease and alcoholism, were highest among those in their sixties.
But Davis, who wrote a commentary in Annals of Internal Medicine, notes the study also showed a significant reduction in the risk of dying the earlier that a smoker quit.
"In the 40s and 50s," he said. "However, it's important to note that even people who quit at old ages will enjoy better health and a longer life expectancy."
The risk of death among smokers age 40 and and older was nearly double that of never-smokers or those who had stopped, prompting Davis to conclude that the study should provide a powerful incentive to quit.