In 1971-3 data on smoking habits, cigarette brand smoked, morning phlegm production, and lung function were recorded for factory workers as part of the Heart Disease Prevention Project. These men were reassessed in 1984 and those who had always smoked cigarettes from the same tar group were compared with those who had dropped one tar group (mean decreases of 6.6 mg tar, 0.1 mg nicotine) and two tar groups (mean decreases of 11.9 mg tar, 0.5 mg nicotine). Over the 13 years, men who had dropped one tar group were significantly more likely (p less than 0.05) to stop producing phlegm, but the effect was less marked for those who had dropped two tar groups. The mean fall in FEV1 was similar in all three groups, but 95% confidence limits showed that although dropping one tar group could be associated with at most a saving of 84 ml over the follow up period, there could be little extra benefit from dropping two tar groups. In 1984, all three groups of smokers excreted similar amounts of nicotine metabolites in the urine, suggesting that men who had dropped two tar groups compensated for the reduced nicotine yield of their cigarettes. This could account for the lack of a dose response relationship between reduction in the tar yield of cigarettes and cessation of phlegm and fall in FEV1.
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