Cigarette tar content and symptoms of chronic bronchitis: Results of the Scottish heart health study

Abstract

Study objective-The aim was to determine if there was a relationship between cigarette tar yield and rates of chronic cough and chronic phlegm. Setting-22 districts across Scotland were used for the Scottish Heart Health Study (SHHS) which was conducted between 1984 and 1986 and from which the data for this analysis were obtained. Subjects-10,359 men and women aged 40-59 years were studied. Of these, 2801 current cigarette smokers whose brand of cigarette smoked was known were selected. Measurements and main results-Data on self reported smoking habits and prevalence of chronic cough and chronic phlegm were obtained from the SHHS. Tar yield was divided into three groups: low (≤12 mg/cigarette); middle (13-14 mg/cigarette); high (≥15 mg/cigarette) . The average tar yield consumed per person was 13.2 mg/cigarette. Women in the middle and high tar groups had smoked for longer and had significantly higher breath carbon monoxide levels, serum thiocyanate levels, serum cotinine levels, and daily cigarette consumption than the women in the low tar group. This pattern was not seen in men for any of these five smoking variables. Rates of chronic cough and chronic phlegm were higher with higher tar yield of cigarettes smoked for women (low tar v high tar: p < 0.001) but not for men. Daily cigarette consumption and the number of years of smoking were the most significant risk factors for chronic cough and chronic phlegm for both men and women. Tar was still a significant risk factor (p < 0.05) for women after controlling for these two risk factors and social class. Conclusions-Both sexes show strong effects of daily cigarette consumption and years of smoking on respiratory symptoms; women show an additional effect of cigarette tar content while men do not. The spread of tar yield in both sexes was small but there were more women on low tar cigarettes and this may have enabled a weak effect of tar to be seen better in them. On the other hand, tar level in women was confounded with other factors. Statistical methods of controlling for this may not have removed this confounding completely.