Psychoneuroimmunology

“How stress impacts the immune system”

Modern psychological conceptions of stress emphasize discrepancies between demands on an individual and resources for coping with those demands, and focus on the psychological processes that lead to an event being experienced as stressful. When demands exceed resources, stress is considered to be the result. This is a definition that Sarafino offered in a recent textbook of health psychology: “Stress is the condition that results when person-environment transactions lead the individual to perceive a discrepancy-whether real or not-between the demands of a situation and the resources of the person’s biological, psychological or social systems” (Sarafino, 1998 p. 70) {Sarafino, E.P. (1998). Health psychology: Biopsychosocial (3rd ed). Wiley.}

A great deal of research has been undertaken to understand the psychological processes involved in the appraisal of stress. Research on stress in relation to the immune system, however, has generally adopted a much more simplistic approach to the assessment of stress. Studies have often employed very crude measures of stress, by counting life events or daily hassles that would be expected to produce stress or by simply asking people about the levels of stress they experience.

There are two basic strategies for investigating stress-infectious illness relationships. One is to conduct experiments in which people are deliberately exposed to infection (“viral challenge” studies), the other is to examine patterns of naturally occurring infections. Evidence about the relationships between stress and susceptibility to infectious illness was reviewed by Cohen & Williamson (1991). Here are some examples of those studies that focused on Upper Respiratory Tract (URT) infections, the most common of which are colds and influenza, both viral infections. Other types of infectious illness they reviewed were recurrences of herpes virus infections, and bacterial infections. {Cohen S. & Williamson, G.M. (1991). Stress and infectious disease in humans. Psychological Bulletin, 109, 5-24.}

These studies focus as much on the timing as on the incidence of colds. Typically, people are asked to keep diaries of life events, and the investigators look for associations between the timing of positive and negative life events and people becoming ill with colds. Studies like these show reductions in positive events and increases in hassles 2 to 4 days before the person becomes ill. That period corresponds more or less to the incubation period of colds.

For example, in an early study of this kind, Meyer & Haggerty (1962) followed 100 members of 16 families over a period of one year, using family diaries to record stressful events, and taking throat cultures every three weeks and at times of reported illness. Daily events that disrupted family life were 4 times more likely to precede than to follow new infections.

In another example, Glaser et al. (1987) followed students through the academic year and compared the numbers of infectious illnesses during exam periods with non-exam periods. Predictably, there were more such illnesses during the exam periods. In a third example, Stone et al. (1987) followed 79 married couples over 3 months, during which time they completed daily checklists of events. Undesirable events increased 3 to 4 days prior to the onset of illness, and desirable events decreased 4 to 5 days prior to onset of illness. {Glaser, R., Rice, J., Sheridan, J., Fertel, R., Stout, J., Speicher, C.E., Pinsky, D., Kotur, M., Post, A., Beck, M. & kiecolt-Glasrer, J.K. (1987) Stress-related immune suppression: health implications. Brain Behavior and Immunity, 1, 7-20}
{Meyer, R.J. & Haggerty, R.T. (1962) Streptococcal infections in families. Pediatrists 9, 539-549}
{Stone, A.A., Reed, B.R. & Neale, J.M. (1987). Changes in daily life event frequency precede episodes of physical symptoms. Journal of Human Stress, 13, 70-74}

Because the common cold is not life-threatening, volunteers can be asked to be exposed to cold viruses without breaching the ethics of research. The basic strategy for this line of investigation is to expose a group of volunteers to cold viruses and examine the extent to which they are infected or go on to become ill with a cold. Those rates can then be compared with other measures like their levels of stress before infection, or baseline psychological variables. {Cohen, S., Tyrell, D.A.J. & Smith, A.P. (1993). Negative life events, perceived stress, negative affect, and susceptibility to the common cold. Journal of Personality and Social Psychology, 64, 131-140.}

Stress has been associated with a number of behavioral changes, many of which have health implications. When we consider the role of the immune system in the effects of stress on health, therefore, we need to be aware of factors other than immune functions that could also mediate a stress-illness association. In her Health Psychology: A Textbook, Jane Ogden (1996) describes studies showing of health-related behaviors associated with stress that included smoking, drinking, and risk taking.
Smoking: Stress has been associated with starting to smoke, amount smoked, and success of attempts to give up. For example, children who changed secondary schools were more likely to begin to smoke than those who did not. Higher levels of stress have also been associated with relapses to smoking after a period of absence.
Alcohol: People have been shown to be more likely to drink when they are feeling anxious or depressed, and work stress in particular has been associated with increased alcohol consumption.
Risk taking and health behaviors: There is evidence that stress is associated with increased risk of accident involvement, and reductions in health promoting behaviors, including healthy eating and exercise. {Ogden, J. (1996). Health Psychology: A Textbook. Open University Press}

References:
1. www.city.londonmet.ac.uk/psychology/”Stress” as a psychological concept;
2. www.city.londonmet.ac.uk/psychology/Studies of naturally occurring infections;
3. www.city.londonmet.ac.uk/psychology/Experimental studies of exposure to infections;
4. www.city.londonmet.ac.uk/psychology/Behavioral responses to stress;
5. (Sarafino, 1998 p. 70) {Sarafino, E.P. (1998). Health psychology: Biopsychosocial (3rd ed). Wiley.}
6. {Cohen S. & Williamson, G.M. (1991). Stress and infectious disease in humans. Psychological Bulletin, 109, 5-24.}
7. {Glaser, R., Rice, J., Sheridan, J., Fertel, R., Stout, J., Speicher, C.E., Pinsky, D., Kotur, M., Post, A., Beck, M. & kiecolt-Glasrer, J.K. (1987) Stress-related immune suppression: health implications. Brain Behavior and Immunity, 1, 7-20}
{Meyer, R.J. & Haggerty, R.T. (1962) Streptococcal infections in families. Pediatrists 9, 539-549}
{Stone, A.A., Reed, B.R. & Neale, J.M. (1987).
8. {Cohen, S., Tyrell, D.A.J. & Smith, A.P. (1993). Negative life events, perceived stress, negative affect, and susceptibility to the common cold. Journal of Personality and Social Psychology, 64, 131-140.}
9. {Ogden, J. (1996). Health Psychology: A Textbook. Open University Press}