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Adapted from the NCI Cancer Bulletin, vol. 5/no. 10, May 13, 2008 (see the current issue).

New data from the Nurses' Health Study confirm the lethal effect of long-term smoking and indicate that starting smoking at an earlier age increases the risk of death from cancers caused by smoking. However, the study also confirms that the risk of death from diseases caused by smoking, including lung cancer, heart disease, stroke, and respiratory disease, drops dramatically after sustained periods of cessation.

Overall, the analysis, published in the May 7, 2008, Journal of the American Medical Association (see the journal abstract), found that nearly two-thirds of deaths among current smokers were caused by cigarette smoking, compared with only 28 percent among former smokers.

The new data come from more than 20 years of follow up on approximately 104,000 women participating in this long-running observational study. A similar report in 1993 was based on 12 years of follow up. The new report includes an expanded array of disease endpoints. Current smokers had a 63 percent increased risk of colorectal cancer compared with people who had never smoked, but no significant increased risk of ovarian cancer.

"Smoking cessation was beneficial for each cause-specific mortality outcome examined," wrote the study's lead author, Dr. Stacey A. Kenfield, and her colleagues from the Harvard School of Public Health. For example, within five years of quitting, the risk of death from lung cancer decreased by 21 percent, while the risk of death from coronary heart disease decreased by 50 percent when compared with people who continued smoking.