摘要：Objectives. This study determined the life extension obtained from stopping smoking at various ages. Methods. We estimated the relation between smoking and mortality among 877 243 respondents to the Cancer Prevention Study II. These estimates were applied to the 1990 US census population to examine the longevity benefits of smoking cessation. Results. Life expectancy among smokers who quit at age 35 exceeded that of continuing smokers by 6.9 to 8.5 years for men and 6.1 to 7.7 years for women. Smokers who quit at younger ages realized greater life extensions. However, even those who quit much later in life gained some benefits: among smokers who quit at age 65 years, men gained 1.4 to 2.0 years of life, and women gained 2.7 to 3.7 years. Conclusions. Stopping smoking as early as possible is important, but cessation at any age provides meaningful life extensions. (Am J Public Health. 2002;92:990–996) Despite the reductions in smoking prevalence that have been achieved since the first surgeon general's report on the consequences of smoking in 1964, smoking remains the leading cause of preventable death in the United States. 1, 2 Approximately 45 million Americans and more than 1.2 billion people worldwide continue to use tobacco. 3 A health message commonly provided to smokers as encouragement to quit is that it is never too late. Smoking cessation has well-documented health benefits. 4 Research has shown that for persons who stopped smoking for a relatively long time, the health benefits experienced—as measured both by relative risk (RR) of mortality in comparison with lifelong nonsmokers and by risk of lung cancer—increased in proportion to the number of years since cessation. 4, 5 Recent estimates from Great Britain show that about 90% of the excess mortality attributable to cigarette smoking can be avoided if persons stop smoking before middle age. 6 Life extension associated with smoking cessation may be a more tangible means of representing the reduction of mortality risk associated with quitting at various ages, compared with reductions in the relative or cumulative risk of death. The objective of this article is to quantify, with US-specific data, the benefit to a smoker of stopping smoking earlier rather than later in terms of life expectancy relative to never smokers and continuing smokers. Such estimates are needed to provide a sounder scientific basis for public health messages and clinical advice given to smokers about the effect of smoking cessation earlier in life on life expectancy. Furthermore, such messages need to be as simple as possible to have maximal effect. Our goals were to identify the life-years that could be saved by stopping smoking at various ages and to determine whether even elderly smokers could reap benefits in terms of life years saved from smoking cessation. We used data from the Cancer Prevention Study II to construct a mortality-prediction model that included detailed information on smoking status and other potential confounding variables. 4, 5 We used relative risk of death by smoking category to predict mortality among 35-year-old Americans in 1990 under differing scenarios of age at smoking cessation. We compared life expectancy under the various cessation scenarios with life expectancy for persons aged 35 years in 1990 who had never smoked and for those who continued to smoke. A major benefit of our study in comparison with past work was its use of the Cancer Prevention Study II to obtain relative risks of smoking. The Cancer Prevention Study II sample was large enough (> 10 million life-years of follow-up) to allow detailed modeling of the effect on mortality both of smoking duration and of age at smoking cessation; such controls would not be possible with a smaller database because of small-cell problems. Furthermore, the Cancer Prevention Study II database is somewhat more nationally representative than the Framingham Heart Study database, 7 and in contrast to the British Doctors Study database, 8 it pertains to the United States and includes a much broader population than that study's single group of professional workers. These other databases are the leading alternatives from which one could obtain relative risk estimates. Finally, we projected mortality decreases after cessation with the 1990 census population and the relative risks obtained from the Cancer Prevention Study II, which provides a realistic estimate of the benefits of smoking cessation on longevity in the American context and allowed us to compare our results with recent findings from Great Britain. 6
