The role of stress in illness
The immune system is a collection of billions of cells, which help defend the body against antigens (foreign agents), like bacteria, viruses and cancerous cells, with the major type of cells being leucocytes (white blood cells). Some immune cells produce antibodies, which bind to antigens and destroy them. When stressed the body’s ability to resist antigens is weakened, increasing vulnerability to infection. Stress does not cause infection, but increases the body’s susceptibility to infectious agents through immunosuppression, the temporary reduction of immune functioning. Stress is associated with conditions like influenza, herpes and chronic-fatigue disorder. Occasional release of cortisol does not damage the immune system, but if produced continually, as with chronic stress, it impairs leucocyte activity and the production of antibodies. Therefore cortisol etc. helps protect against viruses and heal damaged tissues, but too much cortisol etc. suppresses the immune system’s ability to protect the body. Stress also causes damage to the heart and blood vessels, which can result in cardiovascular disorders (CVDs), like hardened arteries, hypertension (high blood pressure) and coronary heart disease, which results from arteries becoming clogged up with fatty deposits. Stress can lead to CVDs directly by bodily stress systems, or indirectly through unhealthy lifestyle, like smoking and drinking.
Fig 14.2 The immune system produces cells in the body that help fight infection
Kiecolt-Glaser (1984) assessed immune system functioning in response to stressful events. 49 male and 26 female volunteer first-year medical students gave blood samples 1 month before sitting their final exams and then again on the first day of their exams, after sitting 2 exam papers. Blood samples were analysed for leucocyte activity, specifically killer cell activity, which are known to fight off viruses and cancerous cells. Questionnaires were also completed to assess psychiatric conditions, loneliness and life events. Killer cell activity was found to be greatly reduced in the second blood samples compared to the first blood samples. Immune activity was also found to be lowest in participants who scored highly for loneliness, stressful life events and psychiatric conditions, such as depression and anxiety. Therefore it was concluded that stress is particularly associated with immunosuppression, especially in those individuals who are exposed to certain types of stressor.
• Cobb & Rose (1973), from comparison of medical records, found that air traffic controllers (in a very stressful job) had higher levels of hypertension and risk of heart disease than other air traffic personnel, illustrating how chronic stress is linked with CVDs.
• Melamed et al. (2006) found that burn-out, characterised by physical, emotional and cognitive fatigue, resulting from prolonged exposure to work-related stress, was associated with heightened levels of CVDs and other cardiovascular-related ailments, illustrating the link between chronic stress and CVDs.
• Kiecolt-Glaser et al. (1995) found that the healing process in women given small wounds took longer in those who cared for senile relatives, suggesting that prolonged, chronic stress weakens immune system functioning.
• Cohen et al. (1993) found that participants were more likely to develop a cold after being subjected to the virus if they had high stress scores, suggesting that stress leads to immunosuppression.
Although prolonged, chronic stress can lead to immunosuppression and infection, short-term acute stress can be enjoyable, like watching horror films, and actually strengthen the immune system and therefore incur greater protection against immunosuppression and illness.
Research has allowed psychologists and clinicians to gain a greater knowledge of how the immune and cardiovascular systems function and, more importantly, how they are affected by short-term and long-term stressors.
There is a wealth of evidence to suggest that stressful lifestyles can have a negative impact upon the immune and cardiovascular systems, which has led to initiatives to encourage people to live more healthy and stress-free lifestyles.
Research investigating the immune system and stress is only correlational and cannot show cause and effect relationships. Other factors may be involved, such as smoking.
Individual differences in personality, age and gender have been seen to affect vulnerability to developing CVDs in response to prolonged stress, which means there is no universal explanation for the role of stress in illness.
Changes in immune system functioning as a response to stress can take time to occur and are not immediately identifiable by research. Longitudinal studies could help to show the functioning of the immune system, in response to stress, over extended periods.
A practical application of research into stress and the immune system is that health practitioners can use knowledge gained to help anticipate problems that occur as a response to stressful situations, like post-operative stress, and use appropriate treatments.