1 Department of Primary Care and General Practice, University of Birmingham, B15 2TT Birmingham, United Kingdom
2 Department of Social Medicine, University of Bristol, BS8 2PR Bristol, United Kingdom
(e-mail: j.a.macleod{at}bham.ac.uk)
The recent paper by Schernhammer et al. (1) in the American Journal of Epidemiology presents the latest evidence on the importance of job stress as a determinant of health in North American nurses. These authors' findings suggest that job stress doesn't cause breast cancer in this group. An earlier paper (2
) suggested that it does not cause heart disease either. Despite these two negative reports regarding the effects of job stress on important objective indicators of women's health, perceptions of job stress are strongly associated with perceptions of health among participants in the Nurses' Health Study (3
). What might explain this apparent anomaly?
Many people believe that the bad feelings they call stress, particularly those associated with their job, influence their physical health (4). This is hardly surprising since scientists have been telling them as much for some time (5
). In addition, irrespective of conscious beliefs about stress, many people appear to have an essentially negative worldview and perceive that they experience both more stress and more illness symptoms, in the absence of any objective evidence that this is the case (6
). Both of these considerations mean that associations between subjective stress and subjective health are likely to be the rule rather than the exception and that such associations generally tell us little about the etiology of physical disease (7
).
The second part of the explanation probably relates to the social patterning of illness and job stress. Most illness is positively associated with social disadvantage. Further, socially advantaged people tend to like their jobs more and perceive that they expose them to less stress. Thus, one would expect that, irrespective of any true causal processes, confounding by disease-causing factors associated with social position would generate an association between psychosocial adversity and illness (8). However, if stress truly mediated this association, it should be apparent whatever the social distribution of either stress or illness. This is why, in this context, it is interesting to study examples of diseases that are not associated with disadvantage or populations where it is not the disadvantaged who feel more stressed (7
, 8
). In North America, breast cancer is not generally associated with disadvantage (9
). However, job stress appears typically patterned among North American nurses, higher stress being associated with lower social position (1
). Conversely, among Scottish men in the 1970s, heart disease was strongly associated with disadvantage, yet it was the socially advantaged who felt themselves to be more stressed (7
, 8
).
Both of these situations provide ideal opportunities to test the hypothesis that stress genuinely causes disease, perhaps through the neuroendocrine pathways typically invoked in this regard. The fact that no such association is apparent (in fact, in both examples higher stress appears weakly protective) strongly suggests that stress doesn't cause physical disease and that instances where it appears to are products of bias and confounding as discussed above. We are not aware of any instance of a robust positive association between stress and objective physical disease being reported from a population where either stress was associated with social advantage (but disease was not) or disease was associated with social advantage (but stress was not).
Negative findings on stress and disease are often accompanied by scholarly and imaginative speculation by psychosocial theorists as to why, despite a general causal relation, the association is absent in a particular data set (10, 11
). Absent from these special pleadings seems to be consideration of the possibility that, other than in instances where it reinforces unhealthy behavior, stress may have no important direct influence on physical health. It seems to us that this latter conclusion is the interpretation that follows from the evidence, so far presented, from the Nurses' Health Study.
ACKNOWLEDGMENTS
Conflict of interest: none declared.
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