Letter: Coronary puzzle

Sir: Jeremy Laurance is delighted at expert puzzlement over results of the World Health Organisation Monica Project, but Monica researchers would not agree that "there was no link - no link at all" between trends in standard risk factors of smoking, blood pressure and cholesterol and trends in heart disease, and that the results are "astonishing".

It is true that there is not a strong relationship, but most trends are down. This creates a statistical problem in estimating how great or how small is the contribution of known risk factors, and therefore how much room is left for other animals in the jungle.

At Monica's launch standard risk factors were known to predict individual risk within populations, but the absolute levels of risk varied between populations more than known risk factors could explain. The project asked how well trends over time in these population levels were explained by changes in standard risk factors. The answer - "not very well" - was more negative than many expected, but had we known the answer beforehand we would not have mounted the project!

Health promotion is about what is known. Many diseases of unknown causation have been controlled by entirely empirical means (eg Jenner and vaccination against smallpox). Prevention is not all-or-nothing. It is the major risk factors which determine whether a chronic disease is common or rare and whether it occurs in young or only elderly people.

Research is about what is not known. Only a fool would use the latter as an argument for complete inaction, for disregarding or going against reasonable advice. Jeremy Laurance's reaction is akin to someone who uses the news that a good driver has been killed in a car accident to justify and encourage bad driving. The Monica findings are certainly a challenge for researchers as to what exactly is going on at a population level but do not change the advice to individuals as to how they might modify their personal risk.

HUGH TUNSTALL-PEDOE

Rapporteur WHO Monica Project

Cardiovascular Epidemiology Unit

University of Dundee