Cigarette Smoking and Mortality Risk

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Abstract
DESPITE WIDESPREAD agreement that cigarette smoking is harmful for health,1-12 some observations in the Seven Countries Study have raised the question whether this is universal. Keys' monograph13 points out that cigarette smoking was much less predictive of coronary heart disease (CHD) and all-causes death in 10 years of follow-up in southern Europe and Japan than in the United States and northern Europe. A more recent analysis of 25-year follow-up data reported that number of cigarettes smoked per day was significantly related to death from stroke both in pooled data and in 3 cohorts, but was statistically significantly inversely related to death from stroke in 1 Greek cohort.14 Besides area of residence,13 it has been suggested that level of lifetime exposure to cigarette smoking, the manner of smoking, the type of cigarette smoked, and the typical CHD rate and serum cholesterol level or blood pressure level in a culture might modify the effects of smoking.13,15,16 On the other hand, chance may explain the few findings in which never smokers had a higher cause-specific death rate than smokers. First, some of the Seven Countries Study areas are small, and never smokers were a relative rarity in the early 1960s when the baseline data were collected. Second, no specific hypothesis exists that smoking is unrelated or inversely related to diseases such as cardiovascular disease or cancer in specific areas; therefore, statistical significance in country-specific analyses should be computed with adjustment for multiple comparisons. Third, data are often more variable in studies that pool data across diverse centers than in studies from a single center.