The harm to benefit ratio of treating mild or moderate hypertension is, in the present state of our ignorance, adverse that is, the probability of harm outweighs the possibility of good. The authors of the Medical Council ResearchTrial, which is the best, if imperfect, evidence available, concluded that if 850 mildly hypertensive patients are given antihypertensive drugs for a year, about one stroke will be prevented. It is, however, impossible to predict which people are most likely to have a stroke if untreated, "so this benefit can be achieved only at the expense of involving a substantial percentage of people in adverse reactions to the drugs, mostly but not all minor".

The likelihood of diagnosing non hypertension increases with age. Dr F. H. Messerli and others from the Ochsner Clinic in Louisiana (New England Journal of Medicine, 13 June 1985) found that half of 24 hypertensive patients over the age of 65 had "pseudo-hypertension". Pseudo-hypertension is a false alarm caused by increased resistance to compression of the artery by the blood pressure cuff because of hardening of the arterial wall. The difference between cuff pressure and true pressure (as measured by direct intra arterial measurement), ranged from 10 to 54 mm Hg with a mean of 16 mm Hg for both systolic and diastolic pressures. This would suggest that about half the patients over 65 whose mean cuff blood pressure was 180/100 had a true blood pressure of less than 165/85, which is normal for their age and would not justify treatment. If these patients' blood pressure were to be lowered by drugs it would not only be inappropriate and wasteful of resources but would also place these people at the risk of side effects and even of death.

Those who advocate the identification of risk markers and who believe that coronary heart disease is preventable often cite the North Karelia experiment. North Karelia is a county in Finland, which had the highest known mortality rates from coronary disease. It was decided that there should be a major county wide campaign in North Karelia to reduce risk markers and that the results would be compared with a neighbouring control county, Kuopio. While morality fell in North Karelia, it also fell in Kuopio and in all the other counties of Finland, where there had been no equivalent attempt to alter risk status.

The other argument which is often used in favour of early intervention is the fall in mortality rates which has occurred in the United States and Australia and some other English speaking countries, and which is ascribed to healthier lifestyle, dietary changes, less smoking, treatment of blood pressure and, maybe, better management of heart attacks. These data are based upon what is written in death certificates. However, a recent careful study in Minnesota showed no change in the rates of heart attacks between 1970 and 1980, a time when national rates were said to be falling. In Sweden, despite a reduction in known "risk factors", coronary mortality in men aged between 40 and 74 is increasing. Another discordant finding is that in a number of countries mortality rates in men and women are moving in opposite directions.

A more probable reason for the failure to show that this disease is preventable is insufficient knowledge about its cause. The long list of risk markers is a tribute to our ignorance, rather than a proof of our knowledge. Coronary disease may not be a single disease; relatively young men's heart attacks may not have the same cause as heart attacks in eighty year old women and both may be different from those people who get heart pain on exertion (angina pectoris) but do not suffer heart attacks.