Background: Based on data from the European Prospective Investigation into Cancer, Norfolk (EPIC-Norfolk) study, we have previously shown a strong sense of coherence (SOC) to be associated with a reduced rate of all-cause mortality.
Objectives: To investigate the extent to which the SOC mortality association can be explained by socioeconomic status and lifestyle choices.
Design and setting: Prospective population-based cohort study.
Participants: 18 287 study participants aged 41–80 years who reported no pre-existing chronic disease at baseline and who completed an assessment of SOC.
Results: Based on 1599 deaths during a mean follow-up of 8.3 years, a strong SOC was associated with a 20% reduced risk of all-cause mortality. Measures of lifestyle choice (cigarette smoking, physical activity, dietary intakes of fruit, vegetables and fibre) and socioeconomic status (social class and education) explained 23% of this association.
Conclusions: The SOC concept embraces multiple sets of chronic disease risk factors that include lifestyle choices and those associated with socioeconomic status, and is a potential aid in understanding differences in health outcomes in similar individuals.
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Sense of coherence (SOC) is hypothesised as a flexible and adaptive dispositional orientation that enables successful coping with adverse experience,1 and has been shown to be associated with perceived good health and predictive of positive health outcomes.2 Based on data from the Norfolk (UK) European Investigation into Cancer (EPIC-Norfolk) study, we have shown previously that a strong SOC was associated with reduced rates of all-cause mortality, independent of established risk factors,3 and that study participants with a strong SOC were less likely to smoke cigarettes, less likely to be physically inactive and to report that they have a higher dietary intake of fruit, vegetables and fibre, independently of social class and education.4 We now investigate the extent to which the association between SOC and all-cause mortality can be accounted for by socioeconomic status and lifestyle choices.
During 1996–2000, a total of 20 921 (of 28 582 eligible EPIC-Norfolk) participants completed the Health and Life Experiences Questionnaire (HLEQ) that included a three-item SOC scale.5 All deaths among EPIC-Norfolk participants to 31 July 2006 were recorded through linkage with data from the UK Office for National Statistics. The association between SOC and all-cause mortality was investigated using Cox proportional hazards regression. The study was approved by the Norwich District Health Authority ethics committee, and all participants gave signed informed consent. Participant exclusions, adjustments and factor codings were chosen to be consistent with previous analyses of these data (see3 4 6 for full details).
Analysis was based on 18 287 EPIC-HLEQ participants (aged 41–80 years) with completed SOC scale scores and who reported no pre-existing chronic disease at baseline. In this sample, a total of 1599 deaths from all causes were recorded during mean follow-up of 8.3 person–years (598 among 7698 participants with a strong (scale score 0 or 1) and 1001 among 10 589 participants with a weak (score 2–6) SOC). Table 1 shows that a strong SOC was associated with an approximately 20% reduced risk of mortality after adjustment for age and sex. There was some evidence of attenuation in the strength of this association over time (p = 0.002 for a test of proportional hazards), although this was not (statistically) significant when SOC was included as a continuous (as opposed to a binary) measure (p = 0.06). Table 1 shows that adjustment for measures of socioeconomic status (social class and education) accounted for 15% of this association, and adjustment for measures of lifestyle choice (cigarette smoking, physical activity and dietary intakes of fruit, vegetables and fibre) accounted for 14%, or 12% after additional adjustment for social class and education. Collectively, these measures explained 23% of the association between SOC and all-cause mortality.
Study participants reporting a strong SOC had a 20% reduced risk of all-cause mortality over 8 years of follow-up compared with those reporting a weak SOC. Measures of socioeconomic status and lifestyle choice accounted for just 23% of this association. However, this study uses a single assessment, relatively late in life, of lifestyle (and of socioeconomic status) that may not provide ideal representation either of overall lifetime exposures or of exposure during periods of greatest risk. Therefore, residual confounding arising from adjustment for these single occasion measures would suggest that lifestyle choices and socioeconomic status could account for a greater proportion of the association between SOC and mortality than is apparent from the analyses presented here.
This study has a number of limitations that should be considered when interpreting these findings. First, the limited age range and selection into the study (which required commitment to extended follow-up, including requests for biological and dietary data) may limit the generalisability of findings. However, EPIC-Norfolk participants have been shown to be representative of the general population of England in terms of anthropometric variables, blood pressure and serum lipids,6 and the study includes participants with a broad range of socioeconomic circumstances,7 although it contains fewer current smokers.6 In addition, this study uses a reduced three-item assessment of SOC, although satisfactory short-term test–retest reliability and validity have been reported for this measure.5
Individuals with a strong SOC appear to be more resilient to the negative effects of social stress.2 For example, SOC has been reported to act as a buffer (effect modifier) against the impact of stressful life events on self-reported health.8 This is consistent with findings from the EPIC-Norfolk study showing that individuals with a strong SOC report more rapid adaptation to their experience of social adversity than those with a weak SOC,9 and that adaptation to stress is associated with all-cause mortality9 and with incident stroke.10 Lifestyle choices represent one likely pathway for the stress-buffering effect of SOC and the associations between adaptation to stress and health. However, our finding that the association between SOC and mortality remained after adjustment for measures of socioeconomic status and lifestyle, and our previous finding that this association was independent of established cardiovascular risk factors,3 suggest that there may be other pathways through which SOC is associated with health.
Evidence in these data of some attenuation in the magnitude of the association between SOC and mortality over time is suggestive of reverse causation whereby individuals with undiagnosed (and perhaps less specific) physical problems at baseline were more likely to report a weak SOC, although our previous finding that SOC was not associated with systolic blood pressure, cholesterol or with pre-existing chronic disease in these data3 is not consistent with this explanation. Our finding that attenuation over time was less evident when SOC was included as a continuous (as opposed to a binary) measure suggests an alternative explanation whereby a single assessment of SOC becomes less representative of exposure risk as endpoints become more remote from assessment, and as those initially at highest risk are increasingly likely to have previously had an incident endpoint. While SOC was hypothesised by Antonovsky as a personal disposition that develops mainly during childhood and early adult life and is relatively stable thereafter,1 11 subsequent studies have shown that SOC is not as stable as had been assumed,12 and is more stable among individuals with a strong as opposed to a weak SOC.13 Instability or otherwise in SOC will have implications for understanding pathways involving social circumstances at different stages over the life course. These issues are likely to be informed through longitudinal studies that are able to take account of changing circumstances over time.
A strong SOC was associated with a reduced risk of mortality in the EPIC-Norfolk cohort. There appear to be multiple explanations why SOC (as measured by a single three-item assessment) is associated with future mortality risk, through confounding by risk factors associated with socioeconomic status, perhaps through a physical state component (confounding by pre-existing preclinical disease)), through pathways mediated by lifestyle choices (independently of socioeconomic status) and through other pathways possibly involving social stress. These findings support SOC as a marker of future disease risk and as a potential aid to understanding differences in health outcomes in similar individuals.
What is already known on this subject
Sense of coherence has been associated with lifestyle choices and with health outcomes, including mortality.
What this study adds
The association between SOC and mortality is not solely due to socioeconomic status or lifestyle choices. There appear to be multiple explanations for the associations between SOC and health.
We thank the participants and general practitioners who took part in this study and the staff associated with the research programme.
Funding: EPIC-Norfolk is supported by programme grants from the Medical Research Council UK (G9502233, G0300128) and Cancer Research UK (C865/A2883) with additional support from the European Union, Stroke Association, British Heart Foundation, Department of Health and the Wellcome Trust.
Competing interests: None.
Ethics approval: The study was approved by the Norwich District Health Authority ethics committee, and all participants gave signed informed consent.
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