If you are at high risk from suffering a heart attack, the chances are that you'll be advised to stop smoking and start a diet that reduces your cholesterol levels.

The trouble is that these long cherished beliefs may not do anything to help you live longer.

This shattering conclusion, which questions the basic assumptions of heart disease prevention treatment, is based on a major American study involving 12,866 men at high risk from developing heart disease. They either joined a special healthcare programme for hypertension or they just carried on with their lives. After seven years, there was virtually no difference in the death rate between the two groups.

So should you keep smoking and avoid changing your diet? Researchers from the Multiple Risk Factor Intervention Trial Research Group, who carried out the study, admit that it is an option that has to be considered. But they suspect that the reason why the death rate was as high in the healthcare group was because of adverse reactions from some of the antihypertensive drugs they were also given.

The researchers say this is "the most likely" reason for the unexpected findings.

So perhaps you should give up smoking and change your diet after all but just keep off the drugs (JAMA, 1997; 277: 582-94).