SERUM VALIDATED TOBACCO USE AND SOCIAL INEQUALITIES IN RISK OF ISCHEMIC-HEART-DISEASE

Background. We have previously shown that the inverse social gradient in risk of ischaemic heart disease (IHD) was not explained by self-rep orted smoking habits. We pursued the issue in a follow-up study 15 yea rs later, where use of tobacco was validated by serum cotinine. Method s. Some 3216 men aged 53-75 years were included in a study on the asso ciation between self-reported tobacco use and serum cotinine concentra tion. The men had their morbidity and mortality recorded over 4 years. Some 2833 men without overt cardiovascular disease were included in t he incidence study. Potential confounders examined were serum lipids, serum selenium, alcohol consumption, physical activity, hypertension, blood pressure, and body mass index. Results, There was a strong posit ive correlation between serum cotinine level and self-reported tobacco smoking: r = 0.68, P < 0.0001. The misclassification rate of smokers as non-smokers was apparently higher in low social class. However, a l arger proportion of men in low social class were users of chewing toba cco or snuff, and, when taking this into account, there was no social gradient (i.e. trend) in the estimated misclassification rates from so cial class I to social class V: 1.0%, 3.8%, 3.2%, 2.0%, 2.3%, P = NS. After validation of use of tobacco with serum cotinine measurements, c ompared with social class I, social class V had an overall significant ly increased risk of IHD, relative risk = 4.5 (95% confidence interval : 1.6-12.9), P < 0.01, which was slightly higher than when no validati on was performed. Conclusions. We conclude that, (i) social difference s in use of tobacco validated by measurements of serum cotinine did no t account for social inequalities in risk of IHD in middle-aged and el derly men, (ii) no significant social differences existed in the miscl assification of smokers as non-smokers, (iii) reclassification of self -reported non-smokers should not be done without due consideration of the use of chewing tobacco and snuff.