Can a decline in the population means of cardiovascular risk factors reduce the number of people at risk?(Statistical Data Included)

Abstract

Objective--To prove the possibility of shifting distribution of cardiovascular risk factors for a whole population over time and thereby to influence the prevalence of the corresponding disease states, according to the theory stated by Geoffrey Rose in 1985.

Design--Examination of standardised data from the German Cardiovascular Prevention Study (GCP), a seven year long, population-based, multicentre intervention trial, concerned with decreasing risk factors for cardiovascular disease. Setting and subjects--three cross sectional surveys of a population 25 to 69 years old in six study regions, and three nationwide cross sectional surveys in the former West Germany in 1984, 1988 and 1991.

Main outcome measures--The relation between the population mean for systolic and diastolic blood pressure, total serum cholesterol, body mass index, and alcohol intake, and the prevalence of the corresponding disease states, as are systolic ([greater than or equal to] 140 and [greater than or equal to]160 mm Hg) and diastolic hypertension ([greater than or equal to]90 and [greater or than or equal to]95 mm Hg), hypercholesterolaemia [greater or than or equal to]250 and [greater or than or equal to]300 mg/dl), overweight (body mass index [greater or than or equal to]30 kg/[m.sup.2]), and heavy drinking (weekly alcohol intake [greater than or equal to]300 g/week). Results are expressed as linear regression equations and Pearson correlation coefficients.

Results--The correlation between the mean population values and prevalence of disease was close for blood pressures and body mass index. The Pearson coefficients, corrected for the influence of values increased above borderlines, were 0.86 and 0.81 respectively for systolic blood pressure, 0.88 and 0.91 for diastolic blood pressure, 0.28 and 0.52 for cholesterol, and 0.86 for the body mass index. The coefficient for alcohol intake was 0.55. Conclusions--It seems possible to shift the risk distribution of a population for some physiological parameters over time with the effect of changing the disease prevalence. This strategy can be used successfully for specific preventive measures, as was strongly advocated by Geoffrey Rose.

Arterial hypertension was proved to widely vary among different geographical regions as well as among different cultural settings. While nomads in Kenya [1] and the Yanomamo Indians in Brazil hardly know this disease, it is quite common in the Western industrialised world. [2]

By looking at the distribution of blood pressure values of these populations, you can see that not only the number of people in the abnormal range differs, but that the whole distribution curve is shifted as well. In this case, the population means of blood pressure and the prevalence of disease states of these--that is, hypertensive blood pressure--will correlate.

In 1990 Geoffrey Rose examined the relation between the population means of several health indicators, like blood pressure, body mass index, alcohol intake and sodium intake, and the corresponding prevalence rates of disease states operationally defined as being above certain values. Using data from a large intercultural epidemiological study (Intersalt) with 52 distinct populations, [2] Rose and Day [3] showed that the population means for physiological as well as for behavioural parameters have an almost linear relation to the prevalence of the corresponding disease states. In this intercultural comparison, populations with higher means also had higher prevalence rates of the diseases. From these results, the authors drew the conclusion that it is possible to predict the number of diseased people in a given population from the mean of the corresponding health indicators in the same population. They stated that the tail of the risk distribution--that is, the high risk people--belongs to its body--that is, t o the "normal" ones. Therefore, they emphasised the collective responsibility of the society for the number of its deviant people.

From this concept, two main preventive strategies can be deduced. The commonly used and traditional strategy in clinical medicine that consists of identifying people at high risk to be treated with appropriate means to reduce individual susceptibility. While this offers a favourable benefit to risk ratio to the patient and makes a cost effective use of medical resources, the underlying causes of the incidence rate within a population are not tackled.

Its aim is to cut off the high end tail of a population's risk distribution by treating only those susceptible to a certain disease.

This so called high risk strategy contrasts with the population strategy, where one tries to change the behaviour or characteristics of the whole population. To this aim, the risk distribution of the entire population has to be moved to a lower risk range. This is a radical approach that has an unexpectedly high potential of prevention for the population, but on the other hand offers only a small benefit to risk ratio to each person. The immediate benefit of the high risk approach can be appreciated easily by the patient and the doctor. The population strategy, however, lacks a large benefit for most people, who would have been well anyway. Its great advantage and challenge lies in the attempt to change the view of what is normal within a population by accepting the population's responsibility for those with deviant values. [4 5]

So far, the underlying theory has been proved only by intercultural comparison of observational data. This paper attempts to add one more piece of evidence to the relation between induced changes of the population mean and prevalence of disease within a population over time. Therefore, the hypothesis of Rose was tested in an intervention study [*]. To this end, we make use of the multiple regional and national surveys in the German Cardiovascular Prevention Study (GCP). [6]

Methods

The GCP was a seven year long, population-based, multicentre intervention trial aiming at reducing risk factors for cardiovascular diseases. In addition to a high risk approach to prevention, a population strategy was also applied. Broad preventive programmes were implemented in overlapping waves in six regions in West Germany. The programmes consisted of educational, behavioural, and medical advice on eating and drinking habits, early detection of hypertension and hypercholesterolaemia, exercise, non-smoking campaigns, and stress …