Health Check: I think I'm sick, therefore I am

A neighbour of ours was mugged not long ago. Walking home, somewhat worse for wear, he was jumped on by three youths, knocked to the ground, glasses sent flying, wallet nicked. A typical London scenario.

Typical, as I say. I know this is happening, in other streets, in other cities all over the country every day. But try as I did, for several weeks after, I could not put it from my mind. Like thousands of others, when walking home in the dark, I found myself glancing over my shoulder, checking who was coming towards me, flinching at sudden sounds. Fear of crime, as we know, is infectious – and now I was infected.

It is often impossible to resist these fears. In March 1996, we gave up eating beef in our household after the Government announced that BSE had spread to humans. In spite of the fact that the period of maximum risk up to 1989 had long since passed, when the use of the spinal cord and other unsavoury bits was banned, we chose to remove steak from the menu.

It was against my better judgement, but the family prevailed. In the years since, I am glad to say, beef has made a reappearance on the household shopping list, as the public commotion around it has abated. The risk hasn't changed, but our fears have.

Our beliefs about facts can be as important to our state of mental and physical health as the facts themselves. But there are also cases in which beliefs can alter the facts.

There was an intriguing study of Gulf war veterans published in the British Medical Journal last week which showed that 17 per cent of them believed they were suffering from Gulf war syndrome.

Given that soldiers are young and selected for their health and fitness, it is remarkable that so many of them report suffering illness which left them distressed, fatigued and miserable. The researchers found that the strongest factor associated with the belief that they had Gulf war syndrome was knowing someone else who had it. The belief, in other words, was infectious.

The researchers, from the Gulf war research unit at King's College School of Medicine, had earlier shown that there is no identifiable cluster of symptoms that could be called "Gulf war syndrome."

Gulf war veterans suffered more illness than those who served in Bosnia or remained at home in the UK, but the illnesses ranged from mild fatigue and headaches to severe urinary and sexual problems and could not be classified together as a single syndrome. Equally, it was unlikely that they had a single cause. Their conclusion was that the beliefs may have been transmitted from one soldier to another, like an infection, because of the army's "buddy" system, which fosters close-knit groups.

"Concern over one's health may lead a person to seek support from peers in a similar position. As a result, a system of beliefs around the illness in which the veterans shared ideas about the nature and cause of their symptoms may have evolved," researchers say.

This goes further. Professor Simon Wessely, consultant psychiatrist at King's College Hospital who led the research, tells me that many veterans are worried they may pass their condition on to their children. They believe they may have been affected by radiation, they know this can affect their genes and they fear similar symptoms emerging in the next generation.

Although studies to date have been reassuring on this point, many veterans have delayed starting a family until the question is settled. But the effect of delay is to increase the likelihood of babies with congenital abnormalities being born, because the risk increases with increasing parental age. So here, a belief about an illness – that it may be passed down the generations – may become self-fulfilling.

The infectious nature of beliefs has been uppermost in my mind since I received a torrent of e-mails in response to piece I wrote on the Comment pages of this paper last week challenging those who claim the MMR (Measles, mumps, rubella) vaccine is unsafe.

While some supported my argument, the majority accused me of being ignorant, unfeeling and insensitive to the plight of parents with autistic children.

None, I regret to say, caused me to change my view. But the heart-rending stories from parents who believe their children were damaged by the vaccine, and the passion with which they were expressed, left me shaken. The fear of vaccination, like the fear of crime, is spreading like a virus. Who, I wondered, exposed to those beliefs could submit their child to the needle without a frisson of anxiety?

Yet I am convinced that the fear of the vaccine will end up doing more damage than the vaccine itself.