Michael J. Thun, MD, MS, and colleagues from the American Cancer Society, Atlanta, conducted a study to determine whether controlling for education, occupation, race, alcohol consumption, and various dietary factors, in addition to age and sex, substantially altered the relative risk (compares the death rate among smokers to that of lifelong non-smokers) and attributable risk (estimates the proportion of deaths caused by smoking) estimates associated with tobacco smoking.
Dr. Thun presented the article here today at a JAMA media briefing on tobacco during the World Conference on Tobacco OR Health.
According to background information cited in the study, the U.S. Surgeon General attributes to cigarette smoking approximately 400,000 deaths annually, approximately one-fifth of all deaths that occur in the United States. Tobacco industry defendants criticize these estimates, arguing that the Centers for Disease Control and Prevention (CDC) method of estimating "smoking attributable" deaths adjusts for age and sex, but fails to consider the lower socioeconomic and educational status and associated dietary, occupational, and other risk factors of modern smokers, thereby exaggerating the number of deaths attributed to smoking.
The study consisted of the Nationwide American Cancer Society prospective cohort study of 974,150 U.S. adults, age 30 years and over, enrolled in 1982 and followed through 1988. (The same study is used for the Surgeon General and CDC estimates of smoking-attributable deaths in the United States.)
The researchers found that adjusting for multiple covariates slightly decreased the relative and attributable risk estimates for current smoking in both men and women, but slightly increased the estimates for former smoking in women. The authors define multiple covariates as factors that may affect health and are associated with smoking, such as lower educational attainment, unhealthy dietary patterns (higher consumption of fat and lower consumption of vegetables and fruit), physical inactivity, and more frequent consumption of alcohol. The overall estimate of deaths attributable to smoking in the U.S. decreased by approximately 1 percent, from 401,109 to 396,741 per year.
"These findings are important because they are based upon the same large prospective study and attributable risk calculation methods that the CDC uses to estimate deaths due to smoking in the U.S.," the researchers write. "The absence of evidence of epidemiologic confounding may help resolve at least one aspect of the ongoing tobacco debate." The researchers define epidemiologic confounding as incorrectly overestimating or underestimating the risk from smoking due to other factors that are more or less common in smokers than in nonsmokers. For example, smokers may consume more fat and fewer vegetables and fruit in their diet than do nonsmokers. Dietary factors may increase heart disease risk.
The authors offer several considerations as to why adjusting for these factors only minimally changes the death estimates. "First, the smokers and lifelong nonsmokers are more similar with respect to socioeconomic and educational status in our study than in the contemporary United States. ... Secondly, not all of the behaviors with which smoking was associated in our study were detrimentally associated with survival [i.e., regular consumption of alcohol]. ... Third, the effect of multivariate adjustment among former smokers, especially in women who have stopped smoking, is to decrease the estimate of smoking-attributable deaths, partly offsetting the increase in the estimate that occurs among male current smokers. [The authors define multivariate adjustment as a statistical approach to separate the risk caused by smoking from other health-related factors that may be associated with smoking by comparing smokers to nonsmokers with similar characteristics. The most common adjustment is for age and sex. Other adjustments include education, diet, physical activity, and alcohol consumption]. The higher educational status and healthy behavior of women who have quit smoking contrast sharply with the characteristics of male current smokers."
(JAMA. 2000; 284: 706-712)
Media Advisory: To contact Michael J. Thun, MD, MS, call Joann Schellenbach at 212-382-2169. On Tuesday, August 8, call the Science News Department at 312-464-5374.
For more information about the Journal of the American Medical Association or to obtain a copy of the study, please contact the Science News Department’s Jim Michalski at 312-464-5785.
E-mail: Jim_Michalski@ama-assn.org
Posted by the Center for the Advancement of Health http://www.cfah.org. For information about the Center, call Petrina Chong, pchong@cfah.org 202-387-2829.
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