Self-reported smoking, cigarette yields and inhalation biochemistry related to the incidence of coronary heart disease: results from the Scottish Heart Health Study.

Background: Smoking is a well-known risk factor for coronary heart disease (CHD). The components of tobacco that cause CHD have not yet been established; nor have the relative dangers of cigarettes of different strengths.

Methods: This is a cohort study of 2,849 men and 2,900 women with no symptoms of CHD at baseline in the Scottish Heart Health Study.

Results: In a 7.7 year follow-up, to 1993, there were 123 male and 49 female CHD events. After adjusting for age, cholesterol and blood pressure, men who smoke > or = 20 cigarettes per day have a relative hazard [95% confidence interval (CI)] of 1.93 (1.15-3.24) compared with non-smokers; for women the corresponding relative hazard is 3.81 (2.00-7.27). Biochemical measures (cotinine, thiocyanate and expired-air CO) are closely correlated with self-reported smoking (0.67 < or = r < or = 0.72), and have similar relationships with CHD. Amongst cigarette smokers, relative hazards (third to first tertile), for tar yield are 1.05 (0.54-2.07) for men and 4.00 (1.13-14.18) for women. Nicotine and CO yields give similar results. Hazard ratios associated with heavy smoking and strong cigarettes are thus much higher for women.

Conclusion: Although smoking was found to have a detrimental effect, this study was unable to suggest a single major cause of CHD. The excess effects found in women compared with men could be due to differences in former smoking habits. Furthermore, risk differences for smoking are slightly greater for men, explained by the relatively low incidence of CHD amongst women.