Beard C M (Department of Health Sciences Research, Section of Clinical Epidemiology, Mayo Clinic and Mayc Foundation, 200 First Street SW, Rochester, MN 55905, USA), Orencia A, Kottke T and Ballard D J. Body mass index and the initial manifestation of coronary heart disease in women aged 40-59 years. International Journal ol Epidemiology 1992; 21: 656-664. A population-based case-control study was conducted to evaluate body mass as a coronary heart disease (CHD) risk factor among women 40-59 years of age. Cases were women aged 40-59 whose first manifestation of CHD was angina (No. = 133), nonfatal myocardial infarction (No. = 90), and sudden unexpected death (No. = 18) during 1960-1982. Two randomly selected controls were matched on age and time of the initial disease manifestation of the case. The adjusted relative risk for weight and body mass index respectively demonstrated a moderate association with all CHD as well as with angina, but no association with definite CHD (myocardial infarction or sudden unexpected death). To determine if the observed association between body mass index and angina was possibly attributable to differential misclassification bias (i.e. obese women were, in contrast to non-obese women, preferentially labelled as having coronary artery disease) data for angina were stratified by confirmed versus unconfirmed cardiac origin. In the unconfirmed angina analysis, the 75th percentile for weight contrasted with the 25th percentile was associated with a 50% increase in the risk of being labelled as having angina (adjusted odds ratio (OR) = 1.59, 95% confidence interval (Cl): 1.11-2.28), while a similar contrast for Quetelet Index was also associated with a nearly 2-fold increase in the risk ol being labelled as having angina (adjusted OR = 1.74, 95% Cl: 1.18-2.57). A 3-fcrfd statistically significant increase in risk of being labelled as having angina was also observed for similar contrasts of weight and Quetelet Index among women with confirmed cardiac origin for their symptoms. These data from the Rochester Coronary Heart Disease project suggest that anthropometric attributes are independent risk factors for angina but not for first myocardial infarction and sudden unexpected death among women aged 40-59 years old. These findings cannot be explained by differential misclassification of obese women. Additional studies of the association between body mass index and CHD among women age 40-59 should precisely define CHD and obesity measures to avoid possible differential misclassification bias.
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ACKNOWLEDGEMENT This project was supported by research grants (HL24326 and AR30582) from the National Institutes of Health, Dr Ballard is supported, in part, by a career development award from the Merck, Sharp & Dohme/ Soriety for Epidemiology Research Clinical Epidemiology Fellowship Program.