Can our minds really control how we are affected by illness? Jerome Burne looks at a major new study
Try this simple experiment. Shut your eyes and think of the last time you had sex. Really go into the details - naked bodies, the touch of flesh, thrusting. You will almost certainly get turned on. Congratulations. You have just demonstrated to yourself that mental events - thoughts and feelings - can have a direct effect on the body. Curiously this very obvious fact, as Paul Martin points out in his new book, The Sickening Mind, is one the medical profession prefers to ignore or even deny.

You might consider that if thoughts can trigger such clear and definite physical responses as erections, blushing and, in the case of hypnosis, a total insensitivity to pain, it would be reasonable to suppose that they could affect our health as well. But no.

Doctors like to deal with what they can see and measure: a viral infection, a malignant tumour; thoughts and feelings are psychiatric territory. This, for instance, comes from an editorial in the prestigious New England Journal of Medicine: "It is time to acknowledge that our belief in disease as a direct reflection of mental state is largely folklore." Or this, from another leading journal: "We have been too ready to accept that mental state is an important factor in the cause and cure of disease."

As these soundbites imply, the hardline medical view is totally at odds with the popular idea - a case of sceptical Roundheads vs woolly-thinking Cavaliers, as Martin puts it. Newspapers and magazines are awash with articles warning of the dangers to health of stress, unemployment and even moving house. And yet it's not that simple. Even among those who meditate to keep their colds away there is still a streak of Roundhead thinking which says that if your illness is going to be taken seriously then there has to be something organically wrong.

This was perfectly illustrated in the recent row over Chronic Fatigue Syndrome or "Yuppie Flu". The problem here is that although sufferers have all sorts of unpleasant symptoms - chronic tiredness, headaches, stiff joints - doctors can find nothing organically wrong with them. There is no evidence for infection and no malfunctioning organ, and so they are classified as having a psychiatric disorder. In other words, their suffering is all in the mind, with the implication of malingering or hypochondria.

This distinction between "real" and "imaginary" symptoms can be traced back, as can so many psychological misconceptions, to Freud. He distinguished between real illnesses and hysterical ones brought on by unconscious emotional conflicts - asthma as the fear of losing parental love, for example. But this is a false dichotomy, says Martin. It is silly to think in terms of either mental or physical, and to prove it he has distilled a mountain of research showing how mental states can affect our health in very physical ways.

Much of the book deals with the way stressful life events can make us ill, or actually kill us. For instance, men who are widowed in their twenties are 17 times more likely to die prematurely than their happily married fellows. On the first day of the Scud missile attacks on Israel in the Gulf war, the death rate from heart attacks rose by 58 per cent.

Even the apparently hard-nosed germ theory of disease doesn't look quite so mechanistic from this perspective. Take colds: studies have shown that only 20 per cent of those exposed to the virus in fact become infected and of those only 25 per cent develop symptoms. In other words, the efficiency of your immune system plays a big part in determining how the virus will affect you, and purely mental factors in turn, such as how in control you feel, how optimistic you are and even how extroverted or introverted you are, can all affect your immune system.

What's more, it now seems that the process isn't one-way. Not only are the brain and the main centres of the immune system connected by a dense network of nerves, but the two systems talk the same chemical language: neurotransmitters affect immune functions and immune antibodies can affect the brain. There is even a theory that schizophrenia may be the result of antibodies, generated while fighting a virus, going on to damage the brain.

So here we have a paradox. We lay people accept as perfectly reasonable the idea that there are links between stress and heart attacks, but we also want to be told there is something really wrong with us when we go to the doctor. Doctors, on the other hand, despite being able to blush and have erections like the rest of us, don't take much notice of these findings when it comes to clinical practice. Why?

What has happened is that both medics and the general public have fallen into an infamous philosophical trap. It is the mind-body problem which, to summarise 2,500 years of philosophising in a couple of sentences, asks what is the relation of the mind to the body. Are they two totally different things, in which case, how do they interact? Or are they are really only one thing? Is the body really an expression of mind, or is mind really only the body, or more specifically, the brain, at work?

Scientific medicine developed in the shadow of the French philosopher Descartes, who "solved" the mind/body problem by declaring the mind an ethereal thing, of a quite different substance to the body. At the time it was a liberating idea and medicine made enormous strides by ignoring mind and treating the body as a mechanical system. In fact, until even 10 years ago, it wasn't just medics who didn't want to know about the mind or consciousness, psychologists weren't interested in it either.

Now consciousness studies are all the rage and, partly as a result of the sort of research Martin has amassed, mind is making a scientific comeback. A new "solution" to the mind/body split, he fashionably suggests, is to look at ourselves in terms of evolution - we are creatures whose physical and mental abilities have evolved because they have survival value, and he goes in for some interesting speculation as to the function of depression and anxiety.

But there he stops. As a biologist - Cambridge and Stamford - he probably felt that he had gone about as far as he could go. On the subject of how all of this new data might actually change current medical practice he is silent, apart from grudgingly admitting that exercise and relaxation are probably a good thing. He virtually ignores the whole realm of complementary medicine. More seriously, he fails to see how the medical profession's current reliance on drugs works to exclude the mind.

Roundhead medics dismiss many of the claims of complementary medicine on the grounds that it hasn't been subjected to the scientific rigours of the double blind trial - giving one group of patients a new drug and one a placebo without telling them which they have been given. But it's not as simple as that. The whole point of double blind trials is to eliminate the powerful natural healing system that swings into action when we believe that someone is going to make us well.

Traditional systems, such as Chinese or the Indian Ayurveda, as well as homeopathy, don't have the mind/body split that runs through Western medicine. Instead, they follow just the sort of principles implied by the research Martin cites. They may prescribe remedies that will affect both mind and body - herbs and meditation, for instance. But who is going to fund expensive trials to test these treatments? Certainly not the drug companies, when there is no prospect of a patentable product to recoup their costs.

Martin's book lets a very interesting cat out of the bag. But he doesn't dare follow it. Ironically, there is some evidence that conventional medicine is already being pushed in a more complementary direction. Complementary medicines are often far cheaper than the latest drugs, which makes them increasingly attractive to NHS fund managers looking at the bottom line.

'The Sickening Mind' is published by HarperCollins, price pounds 16.99