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Association between psychological stress and asthma expression and morbidity
In this issue of Thorax, Archea et al1(see p 139) add to the growing number of studies linking psychological stress to asthma expression and morbidity. To date, studies have reported an association between various measures of life stress and both the onset of asthma or precedent phenotypes2,3 and exacerbations of established disease.4–6 Hypothesised mechanisms underlying the association between stress and asthma expression implicate reciprocal relationships between neural, hormonal and immunological pathways that have been extensively reviewed previously.7,8 Evidence demonstrating that psychological stress influences the expression of inflammatory cytokine patterns in patients with asthma or those at risk of developing the disease supports these theories.9,10 Others have shown that physiological changes, including neuroimmune and genetic processes, may lead to differential responses to therapeutic interventions for asthma and atopic disorders.11,12
The current work by Archea et al1 underscores that psychological factors may also be more indirect, albeit equally important, determinants of asthma morbidity by influencing how individuals perceive and manage their disease. They aimed to examine the relationship between negative life events (NLEs) and asthma-specific quality of life (AQoL), and also to understand the interrelationships among AQoL, asthma severity and socioeconomic status (SES). These cross-sectional results show a relationship between the frequency of experiencing NLEs, a measure of psychological stress, and AQoL among 189 adults with asthma. Those experiencing a greater number of NLEs reported a worse AQoL, a relationship seen across all SES strata. The addition of sex, age, education and race in regression analyses had little effect on the significance of NLEs. When they stratified by income level and severity of asthma, some notable differences emerged. People with more severe disease reported worse AQoL across income strata regardless of the number of life events. Experiencing a higher frequency of NLEs was associated with poorer AQoL, although this relationship was evident with fewer NLEs in the lower income stratum. And finally, in the lowest income category, greater frequency of NLEs was associated with poorer AQoL across all strata of severity. Control for smoking in these analyses had no great influence on the outcome. Future studies examining these relationships in a longitudinal manner are needed to better delineate these associations.
By drawing attention to overlapping research in stress theory, social learning theory and health behaviour research, we may expand on the discussion started by Archea et al1 as to why such differences might be observed. It has been proposed that the association between SES and health disparities may, partly, be determined by increased exposure to acute and chronic stress compounded by the presence of overburdened or absent social supports, psychological morbidity (ie, anxiety and depression) and lack of control over one’s life.13–15 Research on stress has consistently documented that not only are NLEs experienced more frequently among people in lower SES positions but that they are also more strongly emotionally affected by adverse life events.16 Other literature suggests that support systems (eg, social supports and social networks) may serve as protective moderators of life stressors.17 However, groups with lower SES are disadvantaged in their likelihood of experiencing adverse events and also in coping resources they may have available.18
Moreover, ecological views on health recognise that individual-level health risks and behaviours have multilevel determinants, partly influenced by the social context within which individuals live.19,20 Research has begun to explore how the degree of chronic stress is influenced by the characteristics of the communities in which we live. One type of chronic stress that has been investigated in relation to urban health in the US, for example, is neighbourhood disadvantage characterised by the presence of several community-level stressors including poverty, unemployment or underemployment, limited social capital or social cohesion, substandard housing, and high exposure rates to crime or violence.21 Such stress is chronic and can affect all individuals in a given environment regardless of their individual-level risks or life events experienced.
In our laboratory, we have considered exposure to violence in the community as a useful paradigm to understand how chronic social stressors derived from multiple levels may influence asthma burden.22 We showed an association between higher levels of community violence, conceptualised as an indicator of community-level stress, and increased caretaker-reported asthma symptoms among children aged 5–12 years enrolled in the Inner-City Asthma Study.6 In this study, caretaker-reported prevalence of violence in the community, frequency of other NLEs, perceived stress, unwanted thoughts and memories (rumination), caretaker behaviours (eg, keeping children indoors, smoking and medication adherence) and sociodemographic indicators (eg, income, employment, race or ethnicity and housing quality) were ascertained (n = 851). Increased frequency of exposure to violence in the communities predicted a greater number of asthma symptom days among the children in a graded fashion even after controlling for socioeconomic factors and housing dilapidation. This association was partly attenuated by controlling for the frequency of reported experiencing of other NLEs as well as perceived stress and behavioural differences, albeit the trend remained significant. It would be interesting to examine stress in such a multilevel framework in relation to quality of life.
Individuals facing cumulative challenges in poverty-stricken, high-crime, inner-city neighbourhoods23 may be most in need of stress buffers and, yet, the support provided by highly stressed network members may be compromised by the demands that these same people are facing.24–27 The costs of maintaining social networks in lower-income communities may outweigh their benefits—many parents find that protecting themselves and their children from neighbourhood dangers requires withdrawal from the community.28 These and other studies show that being a single parent in such environments may add a further burden. Single parenting and psychological distress have been linked by an unremitting succession of negative events, economic hardship, social isolation and heavy parenting responsibilities.
Then how might increased NLEs be linked to outcomes such as AQoL? When individuals confront environmental demands (life events), they appraise the event(s) as threatening or potentially overwhelming to their existing coping resources. If the events are viewed as taxing, and at the same time coping resources are inadequate, we perceive ourselves to be under stress or distress. Thus, lower-income groups with fewer coping resources and increased cumulative multilevel stress may theoretically be more overwhelmed in the face of fewer individual-level NLEs as reported by Archea et al.1 This perception may, in turn, result in negative emotional states, including anger, anxiety, depression and lower perceived control, which may influence health behaviours including important self-management strategies and adherence behaviours that may affect asthma expression and QoL.7,29 One caveat of this, as pointed out by these and other authors, is that negative affective states may influence both symptom reporting in asthma and QoL measures.30 This needs to be carefully considered in continued work in this discipline.
Although these relationships are complex, as noted earlier, studies such as those by Archea et al1 reported in this issue of Thorax may have considerable implications for asthma management and clinical guidelines. Recognising which groups are most vulnerable to the effects of stress, what stressors are most likely to influence asthma outcomes, paying particular attention to cumulative stressors, and implementing alternative modalities that reduce stress at the individual level may benefit asthma management.31 Understanding and responding to the complex factors that contribute to differences in exposure to environmental factors, including stress based on socioeconomic position on a broader scale (ie, at the population level), may contribute to reducing rising disparities in asthma morbidity worldwide.32
Association between psychological stress and asthma expression and morbidity
Competing interests: None declared.