(After all, who would remember the scientist who discovered that vegetables did not cause cancer? And who remembers the study that showed that saccharine does not cause bladder cancer?) The scientific journals then play up the results to the newspapers to get their names in lights, and many of the newspapers will, in turn, as last week’s events showed, cause as big a sensation as they can. The controversy it may cause is nothing to be frightened of.” Unfortunately, something that starts as a robust debate in the scientific world may cause a public panic. Two cases are not enough for epidemiologists to start looking at the cause of their illness The biological evidence, however, is much more worrying. BSE can be transmitted from sheep to cows and on to cats and zoo animals. Evolutionarily speaking, are we distant enough to escape infection?The real strength of epidemiology is, paradoxically, its biggest weakness.

It functions in the real world, dealing, as Sir Richard Body, an Oxford University epidemiologist puts it, “with things that acutely affect people. Indeed, the recent fear that two boys who have developed brain-wasting Creutzfeld-Jakob disease may have caught it from beef infected with BSE points out the limits of epidemiology. Several researchers have suggested that for a study to be taken seriously, it should demonstrate that a factor increases the risk of disease at least three or four fold But smaller risks are still important – if they are real. The size and especially the design of the study should also be considered critically, but, ideally, an effect should be consistently demonstrated in a number of studies using a variety of research methods.

Most importantly, a plausible biological mechanism for the effect must exist if the link is real, and proof for this mechanism requires an experimental approach in the laboratory. Thus, poor housing, smoking, poor diet and alcohol consumption may all appear to “cause” a whole host of diseases, although only one, or even none, of these factors may be the true cause.But what can be done instead? The challenge for the future is to uncover the smaller risks that remain significant because they are widespread and affect many people. The search to uncover the smaller risk factors continues, as the huge number of epidemiology studies published every year shows. However, recent studies have often been contradictory and have linked cancer with anything from yoghurt to stress. Epidemiology is grinding to a halt and the public is losing confidence. Is there a way forward?To carry out an ideal study you would first select a large group of people from a wide range of backgrounds. Expose half of them to the potential risk you are interested in, and then wait and see how many more people in the risk group die than those in the control group.