May 6, 2008 -- The risk of dying from smoking-related causes drops significantly within just a few years of giving up cigarettes, even for longtime smokers, new research shows.
Within five years of quitting smoking, study participants experienced a 13% reduction in the risk of death from all causes, a 47% risk reduction in heart disease-related deaths, and a 27% reduction in the risk of death from stroke.
Within 20 years of quitting, the risk of dying among former smokers was similar to that of lifetime nonsmokers for most causes of death, with the exception of lung cancer.
The findings suggest that it is never too late to derive health benefits from giving up smoking, says researcher Stacey A. Kenfield, ScD, of the Harvard School of Public Health.
The study appears in the May 7 issue of The Journal of the American Medical Association.
"The most dramatic decreases in mortality were seen within the first five years for many diseases and the risk kept declining over time," Kenfield tells WebMD.
The study included about 105,000 American women participating in the ongoing Nurses Health Study.
The women were between the ages of 30 and 55 at enrollment in 1976. Surviving participants completed detailed health questionnaires every two years for the past three decades.
Between the years 1980 and 2004,12,483 of the women died, with 36% of deaths occurring among women who had never smoked, 29% occurring among current smokers, and 35% occurring among past smokers.
The women in the study who gave up cigarettes smoked for an average of 15 years. Among the major findings from the study:
64% of deaths in current smokers and 28% of deaths in former smokers were attributable to smoking.
The risk of dying from heart disease dropped rapidly within five years of stopping smoking and equalized to that of a never-smoker within 20 years of quitting.
With the exception of lung cancer, the risk of dying from respiratory disease fell to that of a lifetime nonsmoker within 20 years.
The risk of dying from lung cancer dropped by 21% within five years of quitting, but the excess risk did not disappear for a full three decades.
The relationship between the number of cigarettes smoked per day and risk of death varied by disease process. The relationship was weaker for vascular disease, suggesting that "the first few cigarettes account for most of the increased risk," whereas the correlation was stronger for death due to respiratory disease, suggesting that the absolute amount smoked is more critical for these disorders.
Early smokers were most at risk of dying from smoking-related causes. Current smokers who started at age 17 or younger had a significantly higher risk of dying than smokers who took up the habit after age 25. This was especially true for respiratory disease, lung cancer, and other smoking-related cancers.