Changing mortality from coronary heart disease among smokers and nonsmokers over a 20-year interval

A comparison of coronary heart disease (CHD) mortality in two large American Cancer Society studies, Cancer Prevention Study (CPS) I (1959-1965) and CPS-II (1962-1968) suggests that surprisingly large declines occurred in two groups so defined to minimize the influence of change of smoking status. CHD mortality fell essentially in half when comparing nearly 300,000 persons who were actively smoking cigarettes at entry into CPS-I with about 228,000 persons who were similarly actively smoking at entry into CPS-II, about 20 years later. CHD mortality also declined by more than 50% among nearly half a million lifelong nonsmokers recruited for CPS-I in the early 1960s and for CPS-II in the mid-1980s. Possible explanations for these large declines include unmeasured decreases in smoking related to trial design, errors in ascertainment of causes of death, greater improvement among smokers of other risk factors for CHD, and changes in cigarettes or the pattern of smoking that have been salutary for CHD, but not for lung disease or lung cancer; none of these putative explanations can be supported by data from these studies. CHD mortality, much lower in absolute terms in recent years, is still much higher among smokers vs nonsmokers, so that the beneficial trends observed from CPS-I to CPS-II should stimulate further exploration of how CHD is related to smoking, and not serve as an excuse to ignore continued smoking.