Several studies have shown that smoking is a major cause of the lower life expectancy of men compared to women, but there has been no research to assess how far international differences in sex differences in life expectancy and changes in these differences can be accounted for by smoking. This paper gives quantitative estimates of the effects of smoking on sex differences in life expectancy at age 35 years in Denmark, Finland, Norway, Sweden and The Netherlands during 1970-1989. The data on cause-specific mortality by age and sex were obtained from standardized computer-tape transcripts of the WHO mortality data bank. An indirect method based on lung cancer mortality as the indicator of the cumulative effects of smoking was used to estimate the numbers of smoking-attributable deaths in 4 periods. The validity of the method was assessed by comparing the relevant parts of the results with those obtained in 8 national follow-up studies. On average, 2.4 years or more than 40% of the total sex difference in life expectancy in 1970-1974 was estimated to be attributable to smoking in the 5 countries. By 1985-1989 the contribution of smoking dropped to 1.8 years or approximately 30% of the total difference. The contribution of smoking to the sex difference was greatest in The Netherlands and smallest in Sweden. As a result of the decline in smoking-attributable male mortality, the sex difference in life expectancy diminished in Finland in the 1980s. In the other countries the difference continued to grow despite the increase in the loss of female life expectancy caused by smoking.
