Elsevier

The Lancet

Volume 355, Issue 9205, 26 February 2000, Pages 675-687
The Lancet

Articles
Estimation of contribution of changes in classic risk factors to trends in coronary-event rates across the WHO MONICA Project populations

https://doi.org/10.1016/S0140-6736(99)11180-2Get rights and content

Summary

Background

From the mid-1980s to mid-1990s, the WHO MONICA Project monitored coronary events and classic risk factors for coronary heart disease (CHD) in 38 populations from 21 countries. We assessed the extent to which changes in these risk factors explain the variation in the trends in coronary-event rates across the populations.

Methods

In men and women aged 35–64 years, non-fatal myocardial infarction and coronary deaths were registered continuously to assess trends in rates of coronary events. We carried out population surveys to estimate trends in risk factors. Trends in event rates were regressed on trends in risk score and in individual risk factors.

Findings

Smoking rates decreased in most male populations but trends were mixed in women; mean blood pressures and cholesterol concentrations decreased, bodymass index increased, and overall risk scores and coronary-event rates decreased. The model of trends in 10-year coronary-event rates against risk scores and single risk factors showed a poor fit, but this was improved with a 4-year time lag for coronary events. The explanatory power of the analyses was limited by imprecision of the estimates and homogeneity of trends in the study populations.

Interpretation

Changes in the classic risk factors seem to partly explain the variation in population trends in CHD. Residual variance is attributable to difficulties in measurement and analysis, including time lag, and to factors that were not included, such as medical interventions. The results support prevention policies based on the classic risk factors but suggest potential for prevention beyond these.

Introduction

Routinely collected statistics on mortality rates from coronary heart disease (CHD) showed increases in the 1950s and early 1960s in most industrialised countries, but a decline started in the 1960s in the USA and Australia, followed by other countries.1 Key questions were raised at a conference on this decline, convened by the National Institutes of Health in Bethesda, MD, USA, in 1978. Were the mortality changes real, and if so, how much was attributable to change in incidence of coronary events, and how much to change in case fatality? Could the changes in coronary-event rates be related to population trends in the known coronary risk factors of cigarette smoking, blood pressure, and serum cholesterol? Could the changes in case fatality be related to trends in coronary care? These questions could not be answered because of a lack of basic information.2 Consequently, WHO invited investigators with an interest in what was happening to CHD in their own populations in many different countries, to collaborate in an epidemiological study that became the WHO Multinational Monitoring of Trends and Determinants in Cardiovascular Disease (MONICA) Project. Protocols, procedures, and quality-assurance methods were developed for collecting a standard set of data on trends in CHD mortality, non-fatal acute myocardial infarction, coronary care, and major coronary risk factors, in defined populations for men and women aged 35–64 years.3 Apart from fulfilling local needs, the data from the different populations were to be put together centrally to address the unanswered questions from the Bethesda meeting. (For objectives and outline protocol of the WHO MONICA Project see URL: www.ktl.fi/publications/monica/manual/part1/i-1.htm URN: NBN:fi-fe19981147)

In a previous paper, we confirmed the validity of the mortality trends and showed that, in populations in which mortality declined, coronary-event rates contributed two-thirds of the decline and one-third came from change in case fatality.4 The conclusion was that the main determinant of change in CHD mortality was whatever drives changes in rates of coronary events.

The two other questions from Bethesda are now addressed in separate papers. Here we address the first question, formulated for the 1983 protocol as a null hypothesis that for the population reporting units there is no relation between: 10-year trends in the major cardiovascular-disease risk factors of serum cholesterol, blood pressure, and cigarette consumption; and 10-year trends in incidence rate (fatal plus non-fatal attack rates) of CHD.

Relative bodyweight was not originally included in the study protocol for this analysis, but we have included it because of its perceived public-health importance.5

We address the second question, which relates changes in case fatality and other coronary endpoints to changes in coronary care, in another paper in this issue of The Lancet.6 Differences in definitions of populations and in timing of data on risk factors and coronary care inhibit an all-inclusive first analysis of the two questions.

Accumulated evidence of causality through the consistency, strength and reversibility of the classic coronary risk factors in individuals has increased substantially since 1983. The null hypothesis is, therefore, of less importance than estimating the size of the effect. We attempted to estimate the extent to which trends in classic risk factors are driving the change in coronary-event rates at population level. Since the units in this paper are populations, the analysis was ecological.7, 8

Section snippets

Study populations

Study populations consisted of residents of geographically defined areas aged 35–64 years. There was no follow-up of individuals beyond the 28-day duration of a coronary event. The 38 populations in 21 countries were mostly in Europe, but three were in Asia, three in Australasia, and two in North America (table 1). Short descriptions of the populations have been published elsewhere.9 The populations are almost the same as in our previous paper on coronary events,4 except for six that cover

Trends in coronary-event rates and risk factors

The average annual coronary-event rates in the last 5 years of event registration, the means of the risk factors, the risk score in the final survey, and the trends in these are shown in Table 2, Table 3. An average annual change in daily cigarette smoking of 0·5% means that over 10 years, the prevalence of smoking increased by 5 percentage points; likewise an average annual change of systolic blood pressure of −0·69 mm Hg means that, over 10 years, the mean systolic blood pressure of a given

Rationale for the study

From the 1950s onwards, epidemiological studies, led by Framingham in the USA,24 identified personal characteristics as risk factors for the development of premature CHD in previously healthy people. Of these modifiable factors, distinct from age and sex, cigarette smoking, blood pressure, and total blood cholesterol were most consistently and powerfully implicated.25, 26, 27 In the Seven Countries study,28 investigators showed these risk factors to be important within populations in different

Conclusion

The apparent contribution of the classic risk factors to the trends in CHD over 10 years across the WHO MONICA Project populations has been less precisely estimated than had been hoped. Estimates for women were less reliable than those for men because of greater imprecision in the estimation of trends in event rates. Estimates are low, with perhaps 15% in women and 40% in men of the variability of trends in coronary-event rates being “explained” by trends in the major risk factors. How much of

References (52)

  • The World Health Organization MONICA Project (Monitoring Trends and Determinants in Cardiovascular Disease): a major international collaboration

    J Clin Epidemiol

    (1988)
  • FX Pi-Sunyer

    Medical hazards of obesity

    Ann Intern Med

    (1993)
  • G Rose

    Sick individuals and sick populations

    Int J Epidemiol

    (1985)
  • H Morgenstern

    Uses of ecologic analysis in epidemiologic research

    Am J Public Health

    (1982)
  • H Tunstall-Pedoe et al.

    Myocardial infarction and coronary deaths in the World Health Organization MONICA Project: registration procedures, event rates and case fatality in 38 populations from 21 countries in 4 continents

    Circulation

    (1994)
  • U Keil et al.

    WHO MONICA Project: Risk factors

    Int J Epidemiol

    (1989)
  • A Dobson et al.

    Changes in cigarette smoking among adults in 35 populations in the mid 1980s

    Tob Control

    (1998)
  • HK Wolf et al.

    Blood pressure levels in the 41 populations of the WHO MONICA project

    J Hum Hypertens

    (1997)
  • HW Hense et al.

    Assessment of blood pressure measurement quality in the baseline surveys of the WHO MONICA Project

    J Hum Hypertens

    (1995)
  • A Döring et al.

    Methods of total cholesterol measurement in the baseline survey of the WHO MONICA Project

    Rev Épidémiol Santé Publique

    (1990)
  • A Molarius et al.

    Smoking and relative body weight: an international perspective from the WHO MONICA Project

    J Epidemiol Community Health

    (1997)
  • A Dobson et al.

    Changes in estimated coronary risk in the 1980s: data from 38 populations in the WHO NONICA Project

    Ann Med

    (1998)
  • R Clarke et al.

    Underestimation of risk associations due to regression dilution in long-term follow-up of prospective studies

    Am J Epidemiol

    (1999)
  • MR Law et al.

    Systematic underestimation of association between serum cholesterol concentration and ischaemic heart disease in observational studies: data from the BUPA study

    BMJ

    (1994)
  • K Kuulasmaa

    Dobson A for the WHO MONICA Project. Statistical issues related to following populations rather than individuals over time: bulletin of the International Statistical Institute—proceedings of the 51st Session

    (1997)
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