Smoking, estrogen, and prevention of heart disease in women.

Despite the remarkable decline in mortality rates from coronary heart disease (CHD) in the United States (and many other Western na­ tions), it nevertheless remains the leading cause of death among both men and women in the United States. This need not be so. Although much remains to be learned about the causes of heart disease, application of available scientific knowledge would dramatically reduce the cur­ rent high mortality rates. Risk factors for a disease often are most clearly delineated among populations with low to medium rates of occur­ rence; in such a situation, a modest difference in the absolute rates of disease can constitute a fairly high relative risk (or odds ratio) that is easy to discern. For heart disease, studies of young and middle-aged women are especially informative because the rates of CHD in this segment of the population are generally low. The case-control study of CHD in young women by Beard and associates, reported in this issue of the Proceedings (pages 1471 to 1480), focused on four risk factors for heart disease: cigarette smoking, hypertension, diabetes, and lack of postmenopausal estrogens. Of great interest is the statistical analysis that provides not only the odds ratio associated with each of these factors but also an estimate of the proportion of disease potentially attributable to each factor. It is important to realize that these proportions need not total 100%. Because CHD is multifactorial, interventions at several points are pos­ sible, whereas the potential reduction in the rate of disease is calculated for each intervention alone. Thus, according to the data of Beard and colleagues, elimination of smoking in this population might reduce CHD by as much as 64%, elimination of hypertension as a risk factor would reduce CHD by 45%, and use of estrogen replace­ ment in all eligible women could reduce the rate of CHD by 45%. Because cigarette smoking is associated with such a pronounced elevated risk of CHD and because the prevalence of this practice remains high, cigarette smoking must be regarded as the leading avoidable cause of heart disease. In the population of young women in Rochester, Min­ nesota, Beard and co-workers found that ciga­ rette smokers had about 5 times the risk of definite CHD in comparison with those who had never smoked. This substantial increase in risk is consistent with other data from women of comparable age. For example, in the Nurses Health Study cohort of more than 120,000 US female nurses, current smokers had approxi­ mately a twofold to threefold increase in risk of nonfatal myocardial infarction and CHD-related death. 1 A pronounced dose effect was apparent in that study, with relative risks of 4.2 for smok­ ers of 15 to 24 cigarettes per day and 10.8 for women who smoked 45 or more cigarettes per day. Even women smoking as few as one to four cigarettes per day experienced a statistically significant doubling in risk. In that study, half the cases of CHD were attributable to smoking. Beard and associates were unable to assess the effects of cessation of smoking, but other inves­ tigators have demonstrated that the bulk of the excess risk disappears after a year or two. 2