How does stress cause illness

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252 HEALTH PSYCHOLOGY
DOES STRESS CAUSE ILLNESS?
One of the reasons why stress has been studied so consistently is because of its potential
effect on the health of the individual. Research shows that hypertension rates are more
common in those with high stress jobs such as air traffic controllers (Cobb and Rose
1973) than in less stressed occupations such as nuns (Timio et al. 1988). Further, both
cross-sectional and longitudinal studies show that stressful occupations are associated
with an increased risk of coronary heart disease (Karasek et al. 1981; Lynch et al. 1997;
Kivimaki et al. 2002). In addition, Appels and Mulder (1989) and Appels et al. (2002)
indicated that ‘vital exhaustion’ is common in the year preceding a heart attack. In one
study people were given nasal drops either containing viruses responsible for the common
cold or placebo saline drops. Their level of stress was then assessed in terms of life events
during the past year (Cohen et al. 1991). The results showed that not everyone who was
given the virus contracted the virus and not everyone who did contract the virus actually
exhibited cold symptoms and became ill. Stress was shown to predict first who contracted
the virus and second who developed symptoms. However, these studies involved a crosssectional, prospective or retrospective design which raises the problem of causality as it is
unclear whether stress causes illness or illness causes stress (or stress ratings). To solve
this problem some research has used an experimental design which involves inducing
stress and assessing subsequent changes in health. Because of the ethical problems with
such a design most experimental work has been done using animals. A classic series of
animal studies by Manuck, Kaplan and colleagues (e.g. Kaplan et al. 1983; Manuck et al.
1986) experimentally manipulated the social groupings of Bowman Gray monkeys who
have a strong social hierarchy. The results showed that the monkeys illustrated not only
behavioural signs of stress but also a marked increase in the disease of their coronary
arteries. In addition, stress management, which involves experimentally reducing stress
has had some success reducing coronary heart disease (Johnston 1989, 1992) and at
reducing recurrent cold and flu in children (Hewson-Bower and Drummond 2001).
How does stress cause illness?
Johnston (2002) argued that stress can cause illness through two interrelated
mechanisms and developed his model of the stress illness link which involves chronic
and acute processes (see Figure 11.1).
Fig. 11-1 Chronic/acute model of stress–illness link
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