Psychological Stress as a Public Health Problem: How Much Do We Know?

C O M M U N I T Y HEALTH STUDIES V O L U M E XII. N U M B E R 2, I988

PSYCHOLOGICAL STRESS A S A PUBLIC HEALTH PROBLEM: HOW MUCH DO W E KNOW? Neil M. H. Graham

Department

of Community Medic.int., Lhiversitv of Adelaide, S. A , . 5000. interchangeably. Stressors ( sources of stress) can be defined as: 'sociological, psychological and physiological problems with which an individual has been burdened, with demands exceeding his/ her potential ability for adaptation''; or as: 'demands to which there are no readily available or automatic responses and (which) consequently disturb one's emotional homeostasis'.z These definitions are useful because they highlight two important facets of stress theory. These are that the stress-illness relationship is mediated not only by the presence. duration and intensity of environmental stressors but also by an individual's ability to cope with those stressors (Figure I). Coping, in this theoretical framework, is broadly defined and is dependent on factors such as personality, social support, constitutional factors. health practices, lifestyle. education, coping style, control over resources and income. Thus, for a given level of exposure to a range of stressors, it is hypothesised that adequacy of 'coping' will be the major factor in determining whether an individual will proceed to develop an illness. This model has merit in that it can be used t o explain differing individual responses to a given stressor. Also, there is some empirical support for this theoretical construct. There is evidence that p e r s o n a l i t y , ' ' exercise," social group,l occu ation,' control over resources2 and coping style" all may play a role in mediatin the stress,,,IF and social illness relationship. Social networks supports"~ also appear to be important in relation to illness and health, however there is debate over whether social supports have a direct influence on health or act only as buffers between stress and illness.'X~'O Nevertheless, it seems quite possible that these two hypotheses are not necessarily mutually exclusive.

Abstract There is growing evidence that social and environmental stressors increase susceptibility to a range of diseases, including common causes of both morbidity and mortality. Nevertheless, stress is only rarely seriously considered to be a significant risk factor for disease in the public health arena. As a result, attempts at developing rational communitybased strategies and policies t o deal with stress have been isolated or uncoordinated. There appears to be a number of reasons for this situation. Firstly. the strength, validity and reliability of the data relating stress to many disease outcomes has been highly variable. This has mainly been due t o a number of methodological difficulties inherent in this type of research. Secondly, stress management programs often focus on altering the individual response to stress, rather than focusing on changing the social environment to either reduce stressor load or improve the range of coping resourccs available in the community. Thus, this type of activity is often seen as falling within the realm of 'curative' primary health care rather than as a matter for public health policy. Thirdly, since stress is often considered t o be synonymous with 'major life events'the view is often held that because these events are largely unpreventable very little can be done at a public health level. This paper considers these ISSUCS and reviews the current definitions of stress, theories of disease causation, major methodological issues in research, evidence relating stress to a range of disease outcomes and the scope for intervention at a community rather than an individual level. Introduction The idea of a single biological agent as a sufficient explanation for disease causation has become outmoded. The interplay of social, psychological and environmental factors in determining host susceptibility and exposure to disease causing agents is now the accepted paradigm in which most epidemiological and public health research operates. It is within this framework that the relationship between stress and illness is best viewed. Defining stress is difficult, particularly when terms like 'stressor' and 'stress' are frequently used

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Methodological Issues Research into the relationship between stress and illness has been fraught with methodological difficulties. These difficulties broadly fall into three areas: problems defining and measuring stress; difficulty quantifying individual differences in ability to cope with stress, and

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Figure 1: Theoretical framework describing the relationship between environmental stress and illness

Environmental Stressors

Mediating Factors (affect i n g coping

Outcome

1. Personality

1’. Major Life

1. Mental Illness

Events

2. Exercise 2. Chronic Stressors

3. Minor Life Events

111)

3. Income

L

4. Education

5 . Coping Style

2. Psychosomatic Disorders 3. Organic Disease

6. Social Support

7. Lifestyle 8. Constitutional Factors

9. Et Al.

difficult to identify a simple and valid physiological marker of stress to act as a tool for measuring stress in population studies of stress and illness. Also, it is uncertain how hormones which are responsive to some acute, intensive stressors (eg. adrenalin, noradrenalin, cortisol, ACTH, growth hormone, and prolactin) respond to stressors of a less intense but more chronic nature.zsThus, although this approach holds considerable promise and is rapidly advancing, more subjective measures of stress have often been utilised in population research. Examples of subjective, self-report instruments used to measure ‘stress’ include the General Health Questionnaire,26 Langner’s 22-item scale27 and the

study designs that deal inadequately with issues such as the temporal relationship between stress and illness. Initially, following the landmark research of Cannon.2‘ Wolff22 and Selye,*’ stress was generally taken to refer to the non-specific physiological response of the body to a stressor or threat. The centre to this response was assumed to be the adrenal gland and its hormones but it is now clear that the response is far more complicated with evidence that the hypothalamic-pituitary-adrenal axis, the sympathetic nervous system and possibly some brain peptides are all involved.24 Given the complexity of the response it has proven very

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Hopkins Symptom Check-list.28These instruments measure psychological symptoms or ‘distress; and have been purported to represent an individual’s subjective response to social or environmental stressors. However, since some of these scales are also used to measure illness outcomes such as anxiety and depression their specificity and conceptualisation must be open to question. It was probably not until Holmes and Rahe published their ‘Social Readjustment Rating Scale” as a method of measuring major life event stress by questionnaire that interest substantially focused on defining and measuring environmental sources of stress (strictly speaking, these should be referred to as ‘stressors’ but unfortunately the terms tend to be used interchangeably). However, life events represent an incomplete measure of the total environmental stress load’”’’’ and other sources of stress have been examined as shown in Table I. These include chronic stressors,” - ”and minor, day to day stressors (also called minor life events or‘daily Measurement of chronic stressors appears to be an important variable in the stressillness relationship, but the role, definition and measurement of ‘daily hassles’ is still open to debate.’.’ Coupled with the measurement of different sources of stress is the issue of adequately dealing with confounding factors. For example, unemployment, chronic stressors in particular (q. poverty, social/cultural alienation) can be associated with behaviours which in themselves are associated with increased susceptibility to illness, such as high alcohol consumption, smoking and drug use. Although stress can be said to indirectly influence health through these factors, if the principal research aim is to measure the direct effects of stress on health, these factors must be controlled for in any analyses. Unfortunately, this has not always happened in stress research, although the better studies of psychosocial factors and outcomes like cardiovascular and infectious disease have used this approach (discussed later). The second methodological issue concerns measuring individual differences in coping with stressors. A wide range of mediating factors have been identified that may influence an individual’s ability to cope with stress.’ ’’Most studies, however, necessarily focus on only one or two of these mediating factors, most commonly coping style/ behavioursY and social supports/ networks.’+’’ Measuring all these factors in an epidemiological study is not really an option, given the major logistic, financial and analytic difficulties this would present. A different approach is to measure psychological distress in addition to social and environmental stressors. I n this model, individuals coping well with a given stress load would be expected to exhibit few

TABLE 1 Different types of environmental stressors Major Life Events ---

Minor Life Events (‘daily hassles’) more minor, irritating events occurring on a day to day basis examples: traffic, argumentative neighbours, home security, lack of time for recreation, social obligations

Chronic Stressors a long term source of stress in a person’s life; also called ‘role strains’ examples: unemployment, alcoholic or violent spouse, stressful/ unsatisfactory work environment

’’

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significant events in life causing psychological distress or major change in lifestyle examples: divorce, new baby, death of spouse, moving house

psychological symptoms, while those coping poorly would exhibit high lev& of psychological symptoms. Thus, this approach makes no attempt to measure how or why coping is taking place but rather, attempts to quantify the success (i.e., the psychological consequences) of that coping. This approach is, of course, of no benefit in studies of the relationship between stress and mental illness, but has been useful in identifying relationships between stress and perception of health,’9 immune function4 and respiratory infections.4’ The third area of methodological difficulty relates to the temporal relationship between stress and illness. The majority of research in this area has been either cross-sectional or retrospective in design. Thus, it is frequently difficult to determine the direction of causality in these circumstances (does stress cause illness or does illness cause stress‘?).Even when focusing on events that precede illness onset, recall bias in retrospective studies of stress and illness is a major problem (that is, are cases more likely than controls to remember stressful events, even though they are exposed to the same number of events?). Prospective studies are the only effective way of dealing with these issues, but the expense and logistic considerations that these studies often engender may have contributed to the lack of rigorous prospective studies. Probably the cheapest and simplest way of overcoming this would be to include stress measurement variables in prospective studies

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primarily designed to test other hypotheses. Although not ideal, such a pragmatic approach becomes unavoidable where large numbers are needed t o test adequately the stress-illness relationship. Examples where this approach may be necessary include prospective studies of the relationships between stress (and other psychosocial variables) and outcomes such as depression, cardiovascular disease and cancer.

Relationships Between Stress and Illness The relationship between stress and illness has been examined for a wide range of health outcomes. However, for the reasons outlined above, the conclusiveness of the research varies. The following represent areas where there is, at least, some evidence of a relationship between stress and illness. The list is by no means exhaustive, but focuses on topical areas. Mental Illness The association of stress with mental illness has been broadly and relatively rigorously studied over a number of years. A recent large prospective study confirmed that stressful life events significantly increase risk of depressive symptoms in a population.42 It would appear that life events, however, may not be the most important predictor of depression from these results, as a number of other psychosocial variables appeared to be as important in predicting depressive symptoms. Overall, there is little debate now over whether certain stressors increase risk of depression. Research interest appears to be directed more at determining what factors determine vulnerability to stressful The relationship between stressful events and schizophrenia is less ~ l e a r . ~ It ’-~~ seems likely that the relationship is less strong than that with depression and may represent a precipitating factor, rather than a formative/directly causal one. For example, there is evidence that stressful events tend to cluster in the two to three week period preceding the acute onset of schizophrenia48 and may contribute to relapse of schizophrenics undergoing treatment.49 There have been a number of studies examining the role of various stressors in the aetiology of neurosis and increased psychological symptomatology (where no illness, per se, has been defined). The weight of evidence is such that there can be little doubt that stress plays an important role in the develo ment of psychological impairment and neurosis.’*

P

Cardiovascular Disease While there is evidence that life event stress is associated with increased risk of cardiovascular disease other studies have been

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inconclusive on this question.” For some variables, the evidence relating chronic or situational stressors t o ischaemic heart disease (IHD) is more impressive,’*’’’ but the relationships may differ for angina and myocardial infarction as outcomes.@ The overwhelming majority of studies in this area have focused on the relationship between type-A personality and ischaemic heart disease, first described by Friedman and Rosenman.6’ The importance of this relationship remains contentious. This contention is nicely illustrated by the fact that two recent comprehensive reviews of type-A personality and ischaemic heart disease,h2”’ citing almost identical studies, came to largely opposing conclusions. In summary, type-A personality has been associated with increased risk of I H D in a number of large prospective studies62 with one notable exception.64 This latter example focused on high risk men and it is possible that selection bias may have diluted any associations. Nonetheless, this study and the fact that type-A personality does not appear t o be related t o coronary vessel atherosclerosis in angiographic studies63 has raised a number of questions about the robustness of the type-A concept and the mechanisms by which any pathological effects are mediated. These questions remain to be answered, but the evidence relating stress to ventricular tachyarrythmias and sudden cardiac death65 may provide some clues about the apparent relationship between a number of psychosocial factors and cardiovascular disease mortality. Infectious Disease Although not widely studied, there is growing evidence from a number of prospective and longitudinal studies that stress increases susceptibility to acute respiratory infections.J”nn-nu This hypothesis has been strengthened further by studies in humans showing that stress and other psychosocial variables can influence the cellular immune re~ponse’~’~’ and possibly the local humoral immune response.74 Stress also appears to increase susceptibility to either incident cases or relapses of other infectious diseases, particularly infectious mononucleosis,7~herpes ~implex,~6 and periodontal di~ease.~”’~ Cancer The relationship between psychosocial variables and both cancer incidence and ro nosis is an extremely controversial s u b j e ~ tE$dence . ~ ~ ~ ~from well designed prospective studies is sparse, primarily because of the considerable methodological difficulties inherent in studying this relationship prospectively.8’ The evidence that does exist is largely contradictory,82 although one lonpterm,

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contribution stress makes to overall morbidity (and mortality) from mental illness. Some estimates suggest that life events stress may account for as little as 10 per cent in the variance of depression.104 However, the importance of the overall role of chronic stressors is unclear as are the so-called 'vulnerability' factors such as social supports and coping style. Since stress load is more than just life events, it seems likely that 10 per cent may be an under-estimate of the explanatory power of stress variables in mental illness. If stress also contributes to the incidence of conditions like infectious diseases, cardiovascular disease, accidents, headaches, irritable bowel syndrome and utilisation of health services, the costs to the community in terms of morbidity (and possibly mortality), days lost from work and treatment of these conditions must be considerable. Until we know more about the contribution of stress to the aetiology of these conditions the exact magnitude of this community cost will elude us. Similarly, we do not know enough about the levels of stress or exposure to stressors being experienced in thecommunity. Klerman"'5 has tried to give some feel for the health policy importance of stressful life events. In the U.S.A. approximately 2 million people die per year. He assumes that each of these people have between I 3 close relatives and friends who go through a period of mourning and bereavement. Thus, he suggests, approximately 5 million Americans a year are exposed to this very stressful life event. As he points out, the resultant emotional distress, poor sleep, depression and psychosomatic symptoms all lead to increased utilisation of health care facilities and drug intake, so the implications for provision of treatment services and economic loss are substantial. Of course, there is no practical way of preventing this type of major life event, so that the potential for intervention at a population level is not immediately obvious unless innovative programmes can be designed to improve coping resources in the community. However, the discovery that social supports improve coping and may have important effects on health status" I' has substantially increased the scope of such an approach.

prospective study has shown an increased risk of cancer mortality in individuals reporting depressive s y m p t o m s . The ~ ~ evidence for a relationship between stressful life events and cancer incidence appears to be even more tenuous.81 Other studies have focused on mental attitudes, coping and cancer prognosis.RJ8hDespite a notable negative resultx7 this avenue of investigation appears to hold some promise for future research. Overall the question of psychosocial variables increasing cancer risk or changing cancer prognosis remains open, but any effect is unlikely to be large. Use of Heabh Ser viczy

Although not a disease entity, the utilisation of health services is an important area of public health research, particularly for planning and cost-analysis purposes. There is little question that stress is associated with increased use of health services" but the magnitude and importance of this effect is still open to question.')' From a clinical perspective, this research underpins the importance of considering why individual patients choose to present when they do. I t would appear that even when health status and other factors are taken into account, stress levels will influence the decision to attend or not.n* Orher Conditions Stress has also been associated with a long list of other conditions. Stress is a well recognised cause of headache92 and a m e n ~ r r h e a ' ~ ~ and . ' is probably a triggering factor for exacerbations of irritable bowel and asthma." ')' In children, stress has syndrome" ')' been linked with deterioration of blood glucose control in insulin dependent diabetLcs,vy increased incidence of accidentsl(X1and poisonings. l o 1 These latter relationships, although not proven conclusively, all appear to be plausible and fit with anecdotal clinical experience. Koehler'o' has reviewed the evidence for a causal or triggering relationship between stress and rheumatoid arthritis. At this stage the data appear to be inconclusive. Acute life events do not appear to increase risk of peptic ulceration, but chronic stressors may play a role in increasing susceptibility to duodenal

Stress Management Individual Approaches I f we are willing to accept that stress is a public health problem of some importance, then it is clear we need to think more creatively about stress management than we have so far. Stress management tends to be largely thought of in terms of teaching relaxation techniques to individuals and small groups. Whilst the efficacy of this approach has been demonstrated in individuals106 it has limited applicability as a solution from a public

Stress as a Public Health Problem Despite the evidence cited above it is difficult to estimate accurately how important psychological stress is as a public health problem. Part ofthis stems from inconsistent definitions of 'stress' and 'stressors' and part from the inadequacy of data linking stress to many health outcomes. The most convincing data exist in relation to mental health, but what is uncertain is the magnitude of the

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health viewpoint. The principal failing of this approach is that it ignores thesocietalstructuresand attitudes that lead to stressful environmentslo7 and while it may assist with controlling presenting symptoms there is always the major risk of relapse if efforts are not made to change the social environment that has caused the stress in the first place. Community Development and Networking Stress, contrary to popular opinion, appears to be a larger problem in low socio-economic groups and women than in other sectors of societ particularly where social isolation is a problem. ,08,l& In this light, strategies to reduce social isolation hold promise from a public health perspective. There is growing evidence that strong social networks and social supports are associated with lower levels of mental illness, more adequate coping in a stressful environment and perhaps even lower all-cause mortaIity.'"-''' Thus, a community based programme aimed at building supportive networks in areas where social isolation is a significant problem is likely to be worth pursuing further. One possibility as a vehicle for implementing such a strategy may be provided by the current interest of community health workers in'community development' as a process in health promotion. Whilst the ultimate aim of community development is to 'empower individuals to achieve social and health changes',Il0 at the basic level the process most often used to achieve this is social networking. The networking is encouraged through development of self-help groups, food and housing co-ops, community membership schemes and other groups. 110 These groups, when running successfully, incorporate all the features one would expect to see in a supportive social network including information provision, resources, support in times of need and improved self-esteem for individuals. 1 1 1 Thus, even in the short term, the community development process itself may have important effects on health (particularly in reducing psychological distress, mental illness and health services utilisation). This is apart from the long term benefits from any social change engendered by this approach. Whether this is what happens in reality is unknown at this stage, but it would appear to be an area in community health ripe for further research and development as a potential strategy for stress management at a community level. Other Approaches Other potential areas for intervention at an environmental level include the workplace and the so-called urban 'environmental irritants' such as traffic, pollution and poor urban design. Despite a

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considerable body of research, the contribution of workplace stress to total community stress load remains unclear. This is not because there is any doubt that the workplace can be an important source of stress, but few studies have also attempted to determine the concurrent contribution of nonworkplace sources of stress - surely an important confounder in determining total stress load. Another problem is, of course, that in our society there is a significant minority of adults who do not work at all or whose workplace remains in the home. Thus, the role of the workplace in contributing to community stress load remains incompletely described. Although aesthetically unpleasant and undoubtedly contributing to daily 'hassles'34 the level of importance that can be ascribed to traffic, pollution and other urban irritants as a cause of stress in comparison to the other sources of environmental stress (such as major life events or chronic situational stressors) is unknown. It is likely that until better data are available the health consequences of potentially stressful work and urban environments may well be significantly underestimated. Finally, continuing community education on the appropriate use of relaxation, exercise and taking 'time-out' remains as an important option for behaviour change in those who are in a position to change their lifestyle (for example the archetypal stressed business executive), but should not be seen as a panacea.

Future Research Although there are many issues requiring further research in this area, there are three major methodological issues that could be addressed in virtually all stress research. The first is that prospective studies, wherever possible, are preferable to retrospective or cross-sectional studies. Without careful documentation of the temporal sequence linking stress and illness, very little can be discerned about the causality (or otherwise) that we can attribute to observed relationships. The second issue is that measuring stressor load requires a more sophisticated approach than concentrating on life events alone. Other variables that are worth studying are chronic stressors and possibly minor day to day events or 'hassles'. It seems important that in addition to measuring the stressor load, there should be some measure of mediating variables that might determine an individual's susceptibility to illness in a stressful environment (Figure 1). As stated above there is a real need for further research on the effects of social supports o n alleviating health consequences of environmental stress, especially in intervention studies.

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mentioning in the context of this paper. More data are needed on what level of significant stressors are being experienced in the community (such as life events), which parts of society are experiencing the greatest stressor load, what are the major sources of this stress (work or non-work sources, different types of life events, chronic stressors, etc.) and, which factors contribute to coping? With respect to outcomes, virtually all the conditions mentioned in this paper require further research, taking cognisance of the issues raised above. I n conclusion, it is worth stating that stress is worthy of more serious consideration as asubject for systematic public health research. If one accepts the reality of stress as a concept and that stressors lead to increased susceptibility to illness, then to not put more adequate resources into identifying the true nature of the problem seems completely illogical.

The third issue relates to confounding between stressor and outcome measures. This is a problem where outcome measures are not objective and may be measuring the same phenomenon as the stress measures being employed. This is a major problem in studies of stress and psychological impairment, or in studies where symptom scores and psychosomatic disorders $re the outcome variables. Unless measurement instruments and techniques can be shown to be measuring differing phenomena, and clearly separate independent and dependent variables, then this research becomes circular and ends up proving that stress causes stress. This issue has been more fully described elsewhere,s7 although it is worth reiterating that it becomes a non-issue where outcome measures are more objective (for example many biological parameters). There are also some substantive issues worth

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