Evans (1997) argued that acute stressors - i.e. sources of short term stress such as sitting an exam, or a public speaking engagement - have little or no effect on the immune system, but that chronic stressors - that is, long term or persistent sources of stress - do result in more cortisol production and therefore have a knock-on effect in terms of phsyical disease.
Sweeney (1995) looked at people who were chronically stressed (in this case, people who were caring for relatives suffering from dementia), and found that wounds took longer to heal for these people than for non chronically stressed individuals. This does provide support for Evans, although it is difficult to know for certain whether it is a simple cause-and-effect issue.
Most research into the link between stress and illness has been carried out on animals. Riley (1981) put rats on a turntable, and observed that their white-blood cell count went down. He then injected the rats with cancer cells, and found that they were much more likely to develop tumours compared to a control-set of rats who weren't stressed by being subjected to the turntable. This suggests that (assuming the rats found the turntable stressful), the stress made them more susceptible to disease.
H+R developed the Social Readjustment Rating Scale (SRRS) by asking a large set of people to rate a list of life events in terms of how stressful they were. Using this list, an individual can rate how much stress he's been subjected to in the past twelve months; H+R argued that the score given by the scale correlated to levels of physical illness. The list contains such events as "death of spouse", "divorce", "death of close friend", "minor violations of the law".
In a study on navy personnel, H+R assessed stress levels for individuals prior to a term of duty, and then measured how many times each individual visited the doctor while away at sea. They found that there was a correlation between the stress score and number of visits, although this was low (0.118).
SRRS may be criticised because:
One response to criticism of SRRS was Lazarus' list of "daily hassles" which he thought had a cumulative effect and correlated with ill health.
Generally speaking, it has been found that workers occupying lower ranking jobs suffer more stress than their managers. This appears largely to be due to the lack of a sense of control over time and work. While managers have a lot of control over the way that they do their jobs, workers in lower levels are more constrained in the choices they have in how they get their jobs done.
Marmot (1997) found that lower-level clerical workers are four times more likely to experience CVD than their managers. The single biggest predictive factor in their study was the degree of control the person had over their work.
Ganster et al (2001) found that nurses who had little control over their work had higher levels of stress and physical illness compared to nurses who had more control.
This view is supported by an experiment that Weiss conducted in which pairs of rats were subjected to electric shocks that were delivered at regular intervals, with one rat in each pair being able to control the shocks, and the other rat unable to exercise control. Despite the fact that each member of every pair received the same shocks, those rats "in control" developed fewer ulcers than their counterparts.
On the other hand, Brady's "executive monkey" experiment (1958) paired monkeys in a similar way, and delivered shocks at random intervals. In this case, the monkey who had control over the shocks developed more ulcers than the helpless monkey. The key difference here appears to be that the shocks were unpredictable, and the "executive monkey" was on tenterhooks the whole time waiting for the shock so that he could turn it off, while the helpless monkey was resigned to his fate and so less stressed.
Too much, or too difficult, work might be a cause of stress.
Where a person is uncertain about their responsibilities, and may experience stress as a result of trying to cope with conflicting or ambiguous demands.
Cooper (1999) found that black Americans were more prone to hypertension than white Americans - he argued this was "acculturative stress" - due to social factors such as racism and discrimination.
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