A body under stress is a chemically altered body. It is a body awash in hormones and other substances that are normally kept under tight control. In the right proportions, hormones such as catecholamines - including dopamine, epinephrine (adrenaline) and norepinephrine (noradrenaline) - glucocortoids such as cortisol and androgens such as dehydroepiandrosterone (DHEA) keep our bodies healthy. But too much or too little of these substances and they become a form of slow poison, leading to a staggering list of stress-related disorders.

The list now includes fatigue, indigestion, infections, irritability, diarrhoea, eczema, headaches, constipation, psoriasis, muscle tension, peptic ulcer, allergies, neck and back pain, irritable bowel, asthma, atherosclerosis, loss of appetite, nutritional deficiencies, high blood pressure, anorexia nervosa, premenstrual symptoms, diabetes, weight changes, sexual problems, arthritis, insomnia, psychological problems, cancer and depression. Indeed, no part of our lives remains untouched by stress.

The key to stress survival is allostasis - the body’s ability to achieve harmony through change (N Engl J Med, 1998; 338: 171-8). Through allostasis, two adaptive pathways - the hypothalamic-pituitary-adrenal (HPA) axis and the sympatho-adrenal-medullary (SAM) axis which controls the sympathetic nervous system - are initiated. Activation of these pathways leads to many neuroendocrinological changes, such as raised hormones and proteins such as cortisol, epinephrine, norepinephrine, calcitonin, gastrin and insulin, which can result in common fight-or-flight responses such as elevations in blood pressure, heart and sweat rate, coagulation time and blood-glucose levels.

Of these, cortisol and DHEA have been the most widely studied. During episodes of acute stress, hormones such as cortisol at first protect us by activating the body’s defences through a complex chain of biochemical events. But, when these same protective hormones are produced repeatedly or in excess, they create a gradual and steady cascade of harmful physiological changes.

As levels of cortisol rise in response to chronic stress, levels of another hormone - DHEA - drop. The result can be hypothyroidism, heart disease, prostate and breast cancer, menstrual irregularities, osteoporosis and autoimmune disorders such as systemic lupus erythmatosus (SLE) and rheumatoid arthritis (Clin Exp Immunol, 1995; 99: 251-5; Clin Exp Rheumatol, 1992; 10: 25-30).

Most of us think of stress as being emotional in origin. Indeed, most major assessments of life stress take into account events such as bereavement, marriage and unemployment. But the body does not differentiate between these and other kinds of stress, such as physical, chemical, nutritional, traumatic and even psychospiritual. In addition, it is not just major stressors that cause problems. There is evidence that high numbers of small daily hassles can also take their toll (Psychosom Med, 1994; 56: 216-24).

Whatever the source and intensity, the body responds when under attack by releasing a flood of stress hormones to help it maintain balance. The problem is that a body that is constantly adjusting itself to stressors is subject to a great deal of wear and tear. In all this overactivity, the allostatic systems become worn out, leading to an inability to either adapt or shut off (and thus reduce levels of circulating stress hormones) after the resolution of a stressful event (Endocrinol Rev, 1994; 15: 233-60). When this happens, the usual recommendations, such as relaxation and exercise, may no longer be enough to counteract the effects of stress.