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It may seem paradoxical to claim that stress, a physiological mechanism vital to life, is a cause of illness. To resolve this apparent contradiction, we must differentiate between acute stress and chronic stress. Acute stress is the immediate, short-term body response to threat. Chronic stress is activation of the stress mechanisms over long periods of time when a person is exposed to stressors that cannot be escaped either because she does not recognize them or because she has no control over them. Discharges of nervous system, hormonal output and immune changes constitute the flight-or-fight reactions that help us survive immediate danger. These biological responses are adaptive in the emergencies for which nature designed them. But the same stress responses, triggered chronically and without resolution, produce harm and even permanent damage. Chronically high cortisol levels destroy tissue. Chronically elevated adrenalin levels raise the blood pressure and damage the heart. There is extensive documentation of the inhibiting effect of chronic stress on the immune system.
In one study, the activity of immune cells called natural killer (NK) cells were compared in two groups: spousal caregivers of people with Alzheimer’s disease, and age- and health-matched controls. NK cells are front-line troops in the fight against infections and against cancer, having the capacity to attack invading micro-organisms and to destroy cells with malignant mutations. The NK cell functioning of the caregivers was significantly suppressed, even in those whose spouses had died as long as three years previously. The caregivers who reported lower levels of social support also showed the greatest depression in immune activity — just as the loneliest medical students had the most impaired immune systems under the stress of examinations. Another study of caregivers assessed the efficacy of immunization against influenza. In this study 80 per cent among the non-stressed control group developed immunity against the virus, but only 20 per cent of the Alzheimer caregivers were able to do so. The stress of unremitting caregiving inhibited the immune system and left people susceptible to influenza. Research has also shown stress-related delays in tissue repair.
The wounds of Alzheimer caregivers took an average of nine days longer to heal than those of controls. Higher levels of stress cause higher cortisol output via the HPA axis, and cortisol inhibits the activity of the inflammatory cells involved in wound healing. Dental students had a wound deliberately inflicted on their hard palates while they were facing immunology exams and again during vacation. In all of them the wound healed more quickly in the summer. Under stress, their white blood cells produced less of a substance essential to healing. The oft-observed relationship between stress, impaired immunity and illness has given rise to the concept of “diseases of adaptation,” a phrase of Hans Selye’s. The flight-or-fight response, it is argued, was indispensable in an era when early human beings had to confront a natural world of predators and other dangers. In civilized society, however, the flight-fight reaction is triggered in situations where it is neither necessary nor helpful, since we no longer face the same mortal threats to existence. The body’s physiological stress mechanisms are often triggered inappropriately, leading to disease.
There is another way to look at it. The flight-or-fight alarm reaction exists today for the same purpose evolution originally assigned to it: to enable us to survive. What has happened is that we have lost touch with the gut feelings designed to be our warning system. The body mounts a stress response, but the mind is unaware of the threat. We keep ourselves in physiologically stressful situations, with only a dim awareness of distress or no awareness at all.
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