Our findings support the hypothesis that negative life events are associated with quality of life among adults with asthma. This association was observed in a complex set of relationships involving SES and asthma severity. Those in the lower income stratum reported more negative life experiences in the prior 12 months, and it was within that stratum that the number of such events was associated with poorer asthma‐specific quality of life. Those with more severe asthma did not report a greater frequency of negative life events and, in multivariate modelling, asthma severity explained part, but not all of the association of such events with quality of life.
The integration of these contrasting effects yields a relationship that is shown graphically in fig 2. Persons with severe asthma and minimal recent negative life events reported poorer quality of life across income levels. A higher frequency of negative life events, however, was associated with a decrement in asthma‐specific quality of life. This was manifest as fewer negative life events within the lower income stratum, but quality of life was still negatively associated among those with higher incomes given a sufficient burden of negative life events. Among those with the greatest number of negative life events, if combined with lower income, the negative association with quality of life was present across the strata of asthma severity.
We were careful to exclude from this analysis negative life events directly related to personal health status, but we cannot disentangle fully all the potential cause and effect relationships involved. Either negative events or severity of asthma could lead directly to lower income. Indeed, a key set of the negative events we queried have explicit negative financial effects, although others (such as loss of a spouse) certainly could be fiscally as well as emotionally detrimental. Thus, we cannot say whether lower income acts as a mediator of the relationship between negative life events and quality of life or is simply a marker of negative events that also have financial effects. Our and other analyses have shown that asthma is associated with loss of work, decreased work effectiveness, change in working conditions and loss of pay.12,14,32,33,34
Theoretically, this could lead to more reports of selected negative events, yet we did not observe any substantive difference in number of events stratified by either Severity of Asthma Score or FEV1
, making this an unlikely explanation for our findings.
This study is a cross‐sectional analysis. Although the assessment of Severity of Asthma Score and AQOL was assessed via telephone survey that took place before the home visit at which the life events questionnaire was administered, the median time elapsed between the two was only 8 weeks, whereas the recall period for life events was over 12 months before the home visit. We also recognise that the key study measures, by definition, are based on self‐report. Thus, we cannot exclude an element of reporting bias wherein persons with certain traits—for example, anxiety—over‐report negative life events and also respond to questionnaire items consistent with poorer AQOL scores. Arguing against such reporting bias as being a major factor driving our findings is the observation that the AQOL subscale “Health Concerns” was weakest in the association with reported negative life events, and yet this is the subscale that includes worry that asthma is shortening the respondent's life, worry about the future because of asthma, and fear regarding asthma control and drug dependence.25
Although recall bias could also theoretically come into play, surveys of major life events are believed to be relatively unaffected by systematic differences in reporting by disease status.20
We did not analyse the relationship between negative life events and asthma exacerbations. To the extent that increased asthma exacerbations are linked to greater disease severity, our multivariate modelling would have taken this into account and could represent “overadjustment” for this effect. A study of severe life‐threatening asthma among people aged 15–49 years found no difference in the mean number of total negative life events among cases (3.9) compared with controls without asthma admitted to hospital (3.5), but a comparison group of non‐hospitalised people with asthma did report significantly fewer events (2.8).35
A survey of Finnish college students reported that 21% of those with lifetime asthma reported at least one stressful life event, a significantly higher frequency than among controls (13.4%), but exacerbations were not studied.36
A study of childhood asthma (in children aged 6–13 years) found that experiencing a recent severe life event was a risk factor for disease exacerbation in a 3‐week period beginning 1 month after the event.37
These studies support a possible relationship between negative life events and asthma exacerbation. Exacerbation after stressful life events has been the subject of study in several chronic conditions with mixed findings; the most consistent association has been observed in multiple sclerosis.38
We did not explore in depth the potential relationships among psychological status (including depression), quality of life, life events and disease severity. We found a modest association between combined income–severity and life events as joint predictors of SF‐12 mental health score (MCS). MCS was also weakly correlated with AQOL score. Analysis of more specific measures of depressive symptoms could provide additional insights into these associations. The relationship between illness severity and quality of life has been reported previously in analyses based on this cohort and other studies.26,39,40,41,42
A recent systematic literature review on this subject underscores, however, that even the severity–quality of life relationship is complex, depending on the classification of severity used and mental health covariates in the study population.4
Limited data from other analyses of negative life events in relation to quality of life are available. An asthma‐specific study including a life events battery assessed a Serbian translation of the Juniper Asthma Quality of Life instrument.43
Carried out among 160 adults with asthma in Belgrade, interviewed in 2000–2, that study reported that “stressful life events and duration of disease were not limiting factors of the quality of life of asthma patient [sic]” but did not provide data supporting this observation. Using the short form health survey 36 (SF‐36) as a measure of quality of life, a study of 354 adult survivors of testicular cancer found a statistically significant association between the number of negative life events and the mental health subscale, but not the physical health subscale. This analysis took into account cancer treatment and comorbidity, as well as education (which is a common measure of SES).44
A study of 112 persons with breast cancer also found that the number of negative life events (from an abridged battery) was associated with poorer SF‐36 mental health subscale scores assessed 12 months after diagnosis or surgery, taking cancer‐related stress into account, but such a relationship was not noted for physical health.45
Our secondary analysis, using the SF‐12 rather than the SF‐36 and taking into account income and severity, found a weak, non‐significant relationship for physical health (PCS; p
0.10) and mental health (MCS; p
0.11). The weak association we observed may be explained by the differences in measurement of quality of life using a general health status instrument compared with a disease‐specific instrument (the AQOL) and by testing a model that took into account the combined effects of income and disease severity, as well as negative life events.
Our study suggests that negative life events are associated with a decrement in quality of life among adults with asthma, particularly among those whose baseline quality of life is relatively intact. Although wealth may not “buy” good health, better SES seems to buffer the association of negative events and health‐related quality of life. Negative life events, unfortunately, may not be preventable. Nonetheless, those caring for persons with asthma should be aware that after such events, quality of life is likely to deteriorate, especially in certain subsets of patients. Among those people, attention to this potential decline and intervention, where possible, is warranted.