OCCASIONAL TOPIC

TRENDS IN MORTALITY AND POSSIBLE INFLUENCES ON THE DECLINE IN MORTALITY

FROM CARDIOVASCULAR DISEASE

Noel H|ckey, Risteard Mulcahy, la,n Graham and Leslie Daly

Department of Community Medicine and Epidemiology and Department of Preventive Cardiology, St. Vincent's Hospital and University College, Dublin.

Summary

S INCE 1968 mortality from coronary heart disease and most other causes

of death has been declining in the United States, and some other countries. For the first time this century life-expecta- tion in middle-aged people has shown an improvement.

This marked reduction in mortality from coronary heart disease has been accompanied by changes in coronary risk-factors. It is suggested that while no one risk-factor is responsible, the influence of changes in multiple risk- factors could have a direct impact on the improved mortality. Although the data is meagre as yet, similar trends may be occurring in this country during the 1970's.

The importance of monitoring risk- factor trends in Ireland is emphasised. Information concerning trends in mortal- ity and in risk-factors are necessary if conclusions concerning the aetiology of the coronary epidemic are to be reached.

Introduction Epidemics come and go and frequently

physicians are left to wonder what led to their decline. This has been the case with respect to many of the infections common in the earlier part of this cen- tury, notably tuberculosis. In particular, the contribution of preventive and cura- tive medicine to the control of disease has been inadequately understood.

Over the past 40 years we have wit- nessed a widespread increase in mortal-

ity from coronary heart disease (CHD) in most Western countries. Most card- iologists and epidemiologists probably accept that this increase has been real, rather than due to differences in death certification, changing diagnosis or other secular changes (Hickey and Mulcahy, 1970). Extensive clinical, epidemiologi- cal and pathological research has indi- cated that there are many factors which have have influenced the rise of the coronary epidemic. Mortality trends in the United States and a few other coun- tries (Proc. of Conference US Dept. H.E.W., 1979), indicate that the epidemic is now on the wane.

Clearly, it is important to determine what may be influencing the present mortality trend. Because the mortality from CHD in Ireland may be commenc- ing a downward course, it is pertinent that we consider the epidemiological situation in this country.

International Trends in CHD Mortality

It is only now apparent that there has been a general decline in CHD mortality in the United States, at least since 1968, and possibly earlier. This trend was not initially obvious because of failure to appreciate that age-adjusted death rates were necessary to obviate the effect of ageing in the population. The decrease in CHD mortality between 1968 and 1977 was 23.4%. While no other country has exhibited so great a fall in CHD mortality as the United States, similar trends ap-

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TRENDS IN MORTALITY FROM CARDIOVASCULAR DISEASE 405

pear to be taking place in Finland, Can- ada and Australia (Epstein and Pisa, 1979).

Social Class Trends Prior to about 1960, CHD mortality in

the Uuited Kingdom was greatest in the upper and middle classes. Since then, a rise in CHD mortality in working class men and women has resulted in this group now suffering the highest death rate from this condition.

In the United States between 1950 and 1967, the percentage increase from ath- erosclerotic heart disease was greater for non-whites than for whites, especially in males. Since the 1960's, the declining trend for CHD has been most marked in non-whites. Thus, while the earlier in- crease in mortality was most marked in the United States non-whites, the recent decline in mortality is also evident in the same group.

Coronary Risk-Factor Trends There is little doubt that many factors

contributed to the development of CHD epidemics during this century. Although the known risk-factors may not fully explain the increase in CDH mortality, it is clear that cigarette smoking, hyperten. sion and hyperlipidaemia exerted a major influence.

There has been a reduction in the intensity of the major risk-factors in recent years, at least in the United States. The Framingham offspring study (Feinleib et al, 1975) suggests a reduc- tion in mean serum cholesterol of 5-10 ma/dl. Other reports (Abraham et al, 1977; Stamler, 1978) confirm a somewhat lesser or greater reduction in cholesterol. Certain groups have shown a reduction in cigarette smoking, for example, among men aged 45-54 years (Kleinman et al, 1979). Mortality associated with hyper- tension has declined substantially since the 1950's but is evident as far back as 1920. This reduced mortality may in part be the result of improved public educa-

tion and medical care. The hypertension detection and follow-up programme (1977) indicates a changing status of public awareness of hypertension. Re- sults from the same study (1979) show a significantly improved mortality in patients with a 'stepped up care' prog- ramme of hypertensive management.

Such apparently modest reduction in risk-factors might not exert a detectable influence on the longevity of the individ- ual but would be expected to appreciably reduce mortality in a large population. Based on Framingham data a multiple logistic function analysis using 3 major risk-factors has been used to estimate the expected decline in deaths associa- ted with reductions in these risk-factors (Multiple risk-factors Intervention Trial Group, 1977). A population decrease in serum cholesterol of 5 mg/dl predicts a 4.3% decline in CHD mortality. A 2 mm hg reduction in diastolic pressure pre- dicts an 8.7% decline and a 20% reduc- tion in cigarette smoking predicts a 10.5% decline in CHD mortality (Beagle- hole et al, 1979). Taken together, the expected mortality reduction would be 21.8%, close indeed to the observed re- duction in CHD deaths in the United States.

No single risk-factor change can ac- count for the decline in CHD mortality in the United States. The relationship be- tween changes in smoking habits and mortality are particularly complex, For example, smoking can hardly account for the reduction in CHD among women, as American women have not reduced their cigarette consumption. Utah, a pre- dominantly non-smoking State, has shown a similar decline in CHD mortality to the rest of the United States. On the other hand, Doll and Peto (1976) have related the redu6ed mortality from CHD among doctors to a reduction in cigar- rette smoking.

Hospital Care It is possible that Coronary Care Units,

rehabilitation and secondary prevention

406 IRISH JOURNAL OF MEDICAL SCIENCE

programmes may have contributed to the decline in CHD mortality. Until there is good evidence that not only mortality, but also morbidity, has declined, it is difficult not to believe that medical care has contributed, at least in part, to the reduced mortality. This contr ibution is, however, l ikely to be small.

Rose (1975) estimates that the impact of Coronary Care Units on the overall reduction in CHD mortality in the com- munity would not exceed 4%, despite the reduction in coronary care unit mor- tality since the late 1960's. The majority of CHD deaths occur outside of hospital. There is no good evidence that a reduc- tion in mortal i ty among survivors of acute CHD has occurred over the period 1961 to 1976. This might suggest that efforts at secondary prevention and re- habil i tation have not influenced the pre- sent trend of decl ining mortality from CHD. It has been suggested that drugs, including beta-blockers and sulfinpyra- zone (Anturan) may improve prognosis and reduce mortality. Beta-blocking drugs are not widely used in the United States and sulfinpyrazone was intro- duced too late to have influenced mor- tality trends.

Aortocoronary bypass surgery has been increasingly employed in the man- agement of angina pectoris since the 1960's. No scientif ical ly acceptable study has demonstrated a reduction of overall CHD mortality after this procedure, al- though the longevity of certain sub- groups, such as those with left main lesions and those with 3-vessel disease (Graham, 1978) may be increased.

increase in total cancer mortality is due entirely from lung cancer.

Excluding cancer and cardiovascular disease, overall mortality in the United States has been fall ing since the 1960's. This reduction in mortality includes a 3-fold reduction in mortality from influ- enza and pneumonia and a 2.5% reduc- tion in deaths from accidents and "al l other diseases". This overall reduction in mortality has led to an improvement in life-expectation at birth, from 69.7 years in 1960 to 72.8 years in 1976; and at age 45 years, from 29.4 years to 31.5 years. For the first time this century an increase in life-expectation has been demonstra- ted for middle-aged people.

With the exception of lung cancer, chronic lung disease and suic ide/homi- cide, most causes of death are decl ining in the United States at about the same rate as that from CHD. This may suggest that one or a number of generally healthy influences are operating in the commun- ity.

Mortality Trends from CHD In Ireland Table I shows the overall mortality rate

in this country over the period 1960-1978 for CHD, total cardiovascular disease, cancer and all causes. Caution must be expressed in interpreting these data. Mortality rates for 1978 were based upon the 1979 census of population of 3,311,000. The estimated population in

TABLE I

Mortality rates (per 1,000) for selected causes of death in Ireland. Men and women of all ages.

Total All Year CHD CVD Cancer causes

Mortality Trends for Non-Cardiovascular Disorders 1960

By the 1950's in the United States, 1965 cardiovascular disease and cancer were 1970 the principle causes of death. With the exception of lung cancer, mortality from 1975 cancer commenced fall ing from the 1978 1940's up to the present. The continued

3.15 4.63 1.67 11.53

3.01 4.40 1.73 11.50

3.36 5.70 1.80 11.44

3.36 5.40 1.97 10.61

2.66 3.50 1.84 9.90

TRENDS IN MORTALITY FROM CARDIOVASCULAR DISEASE 407

1975 was 3,127,000 and in 1970 was 2,944,000. Populat ion growth may have occurred ear l ier than expected. Assum- ing that this growth operated s ince the ear ly 1970's, the ef fect on overal l mor- ta l i ty could be substant ia l . This ef fect would be to accentuate an ear l ier trend of decreas ing total morta l i ty , mor ta l i ty f rom CHD and total ca rd iovascu la r mor- tal i ty. However, because age-adjusted rates are not ava i lab le at present, it is of course, possib le that the trend of de- creas ing mor ta l i ty f rom al l causes and for card iovascu la r d isease observed in the table, is apparent rather than real.

Risk-Factor Trends in Ireland

There is some ev idence that c igaret te smoking, hyper tens ion and elevated cholestero l levels have shown a reduc- t ion in I reland dur ing the past 2 decades. Pat ients with acute CHD at tending one hospi ta l have shown a progress ive re- duct ion in r isk- factor status between 1971 and 1976. These changes in cigar- rette smoking habits, b lood pressure and cholestero l levels among hospi tal pat- ients may be ref lect ing s im i la r t rends in the general populat ion. The consumpt ion of tobacco has also decreased in I reland and this probab ly more apparent in soc- ial c lasses I and II than in social c lasses IV and V. Data f rom the Ir ish Heart Foundat ion blood pressure screening p rogramme (unpubl ished, 1980) suggests that the f requency of undetected hyper- tension has fa l len s ince ear ly 1970's.

If ca rd iovascu la r mor ta l i t y has shown an improvement over the 1970's, it is of cons iderab le impor tance that research be devoted to ascer ta in ing with certainty, if cor responding t rends in coronary risk- fac tors have occurred. Only in this way can there be re l iab le in format ion con- cern ing the possib le fac tors in f luencing the dec l ine in morta l i ty . Otherwise, the vast expense of t ime and money which has been incurred in researc ing the ae t io logy of coronary heart d isease wi l l end in confusion and controversy.

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