to be infected with cold viruses than those with the least stress, and twice as likely to develop a cold. Moreover, these associations between stress, infection and illness held up even after the data had been adjusted statistically to remove any effects of other potentially relevant factors, including the subjects’ age, sex, prior health, allergies, smoking and drinking habits, sleep and exercise patterns, diet, weight and education.
The technique of deliberately exposing the subjects to viruses ensured that they all had an equal opportunity to be infected. But you can be exposed to viruses without being infected. When you travel in a crowded train or bus you are regularly showered with exotic bacteria and viruses, but fortunately infection does not inevitably follow. Most of the time the bugs fail to make it past your skin or penetrate your inhospitable orifices. To establish that you have actually been infected it must be possible to recover viruses from your blood or body fluids, or show that your immune system has generated antibodies against the virus.
Exposure to viruses and subsequent infection are not the only steps along the path to illness, however. Not every infection develops into a clinical disease. The number of colds you will suffer in a lifetime represents a minuscule fraction of the number of cold virus infections you have had.
Detailed analysis of this experimental data enabled Cohen and his colleagues to tease apart the influences of stress on these two distinct components of disease. Whether or not someone was infected by the cold viruses depended primarily on how they were feeling at the time, especially their current perception of stress and negative emotions. But once they had been infected their chances of going on to develop a clinical cold depended more on their previous exposure to stressful life events than their current emotional state.
These results illustrate a general point: an individual’s psychological state can exert different influences on the various steps in the pathway to disease, from initial exposure to disease-causing viruses or bacteria, through infection by those viruses or bacteria, to the development of disease symptoms and the behavioural response to those symptoms.
We have sampled some of the extensive evidence that what goes on in people’s minds really does affect their chances of becoming ill or dying. The next question is how. It is time to consider the question of mechanism.
3 Psyche’s Machine: The Inside Story
Her pure and eloquent blood
Spoke in her cheeks, and so distinctly wrought,
That one might almost say, her body thought.
John Donne, Of the Progress of the Soul,
‘Second Anniversary’ (1612)
By what means does the mind influence human susceptibility to disease? How can insubstantial thoughts or emotions produce a cold, let alone heart disease or cancer? After all, colds are caused by viruses not thoughts. We have seen evidence that our mental and physical states affect each other; what we need now is an explanation of how they do this. We need a mechanism.
In this chapter we shall explore the biological and psychological pathways by which the mind influences physical health – and, as we shall see, how physical health in turn influences the mind. This is the inside story of how the mind and body interact. There are three main strands to this story. First, our minds can make us believe we are ill, whether or not we really are ill in any objective, clinical sense. Our psychological and emotional state affects our perception of bodily symptoms and our reaction to those symptoms. This is the familiar (and generally misleading) connotation behind terms such as ‘psychosomatic’. But the mind does more than influence our perception of physical wellbeing: it can genuinely affect our physical health. We come now to the second and third strands of the story.
The mind impinges on physical health in two fundamentally different ways: through our behaviour and, more directly, through our body chemistry. Psychological and emotional factors can lead us to behave in unhealthy or self-destructive ways which increase the risks of disease, injury or death. Smoking is an obvious example. Meanwhile, beneath the surface, our mental state can alter our susceptibility to disease by influencing the body’s biological defence mechanisms, most notably the immune system.
There is a fundamental distinction between illness – the sufferer’s belief that something is wrong with them – and disease, which is a definable medical disorder that can be objectively identified according to agreed criteria. You can have a disease (such as early-stage cancer or coronary heart disease) yet not feel ill. Conversely, you can feel ill even though a doctor cannot detect any evidence of disease.
Many people who end up presenting themselves to a doctor have no identifiable organic disease. There is apparently nothing physically wrong with them. Yet they are still there in large numbers, claiming (and, in most cases, genuinely believing) that they are unwell. They are often referred to in rather loaded terms as ‘the worried well’. But the majority of those who are suffering from vague, undiagnosed illnesses are not malingering. They really do feel ill and their ability to lead a normal life may be significantly impaired.
According to a report by the Royal College of Physicians and the Royal College of Psychiatrists, as many as half of all those who present themselves as out-patients for ostensibly medical reasons are suffering from psychological problems. Although they have physical symptoms such as pains, palpitations or breathlessness they have no detectable physical disease. Doctors perhaps understandably focus on the physical symptoms rather than the psychological problems. One consequence is that huge amounts of time and money are wasted on diagnostic tests and treatments for elusive diseases.
A substantial proportion of patients – a fifth or more – prove very difficult for doctors to deal with. Either their illness cannot be diagnosed at all, or, when a diagnosis is proposed, they find it unacceptable. Their treatment, if any, is frequently ineffective and they keep returning to the doctor over and over again, distressed and dissatisfied. These are the so-called heartsink patients. To make sense of what is going on we must once again turn to the mind.
Health and illness lie along a continuum. Often the dividing line between the two is arbitrary, and as much a reflection of our perceptions and expectations as it is of our true state of physical health. Our psychological and emotional state affects our sensitivity to bodily symptoms, our perception and interpretation of those symptoms and, finally, our propensity to seek medical help – whether or not those symptoms reflect a genuine disease.
Those who seek medical care do so because they have noticed certain symptoms, concluded that these symptoms constitute a real or potential illness, and decided to take action. Each of these steps is open to psychological and emotional influences. Individuals differ enormously in the extent to which they monitor their own health; in their willingness to put up with pain, discomfort and worry; and in their readiness to do something about it. The processes that culminate in a decision to visit the doctor depend on factors that are unique to each individual, including their social and financial circumstances, personality, experience, cultural background and genetic make-up. A lot can also depend on their current psychological and emotional state.
When a person is stressed or anxious they may become preoccupied with their health. There is a greater likelihood that they will notice (or imagine) physical symptoms; interpret those symptoms as indications of disease; and become sufficiently anxious about them to visit a doctor. They may also be more in need of the personal attention that they are perhaps not getting from others.
The heightened arousal that accompanies anxiety can make subtle bodily symptoms more noticeable. Moreover, the physiological changes that often accompany anxiety, such as headaches, churning guts or palpitations, may be interpreted as symptoms of disease. The mind can unconsciously create a medical mountain out of a molehill.