Background Most prospective studies on the relationship between sense of coherence (SOC) and mental health have been conducted using subjective health indicators and short-term follow-ups. The objective of this prospective occupational cohort study was to examine whether a strong sense of coherence is a protective factor against psychiatric disorders over a long period of time.
Methods The study was conducted in a multinational forest industry corporation with domicile in Finland. Participants were 8029 Finnish industrial employees aged 18–65 at baseline (1986). Questionnaire survey data on SOC and other factors were collected at baseline; records of hospital admissions for psychiatric disorders and suicide attempt were derived from the National Hospital Discharge Register, while records of deaths due to suicide were derived from the National Death Registry up until 2006.
Results During the 19-year follow-up, 406 participants with no prior admissions were admitted to hospital for psychiatric disorders (n=351) or suicide attempt (n=25) or committed a suicide (n=30). A strong SOC was associated with about 40% decreased risk of psychiatric disorder. This association was not accounted for by mental health-related baseline characteristics, such as sex, age, marital status, education, occupational status, work environment, risk behaviours or psychological distress. The result was replicated in a subcohort of participants who did not report an elevated level of psychological distress at baseline (hazard ratio=0.59, 95% CI 0.40 to 0.86).
Conclusions A strong SOC is associated with reduced risk of psychiatric disorders during a long time period.
- Psychiatric morbidity
- prospective studies
- sense of coherence
- psychosocial epidemiology
- psychosocial influen
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- Psychiatric morbidity
- prospective studies
- sense of coherence
- psychosocial epidemiology
- psychosocial influen
A few decades ago, medical sociologist Aaron Antonovsky1 developed the salutogenic theory of health, which was intended to complement the existing health theories described, for example, in psychiatric classifications. Among various theories on health, Antonovsky's theory focuses on people's health-promoting and health-protecting characteristics. The salutogenic model intends to explain what keeps individuals healthier and less ill, on a continuum between health and illness. Sense of coherence (SOC) is the key construct of this model. According to Antonovsky, SOC is a resource that enables people to manage tension, to reflect on their external and internal resources, and resolve tension in a health-promoting way.2 It is an individual characteristic related to a positive life orientation that may facilitate the development and maintenance of good mental health. A strong SOC indicates that a person feels life makes sense emotionally, perceives stimuli in a clear and structured way and is confident that adequate coping resources are available.
Supporting the model, longitudinal studies have shown the relationship of SOC to various indicators of health,3–5 in particular to mental health.2 6 In a 5-year follow-up, SOC predicted later diagnosed psychiatric disorders,7 and in a 1-year follow-up, it was a significant determinant of depressive disorders.8 Strong SOC has also been associated with fewer depressive symptoms in patients with multiple sclerosis9 and scleroderma,10 and has also predicted subjective well-being among people facing difficulties in their lives.11 12
The aim of this study was to examine whether a strong SOC protects against new-onset psychiatric disorder using large prospective data on Finnish employees who did not have a history of hospitalisation for a psychiatric disorder at baseline. This study adds to the literature in several ways. First, earlier large longitudinal studies on SOC have mainly examined general outcomes, such as all-cause mortality,4 disability pensions13 or subjective state of health,5 but little is known about whether SOC predicts specific diagnosed psychiatric disorders. Second, the possibility that SOC and mental health are overlapping constructs has remained,14 as earlier studies have mainly relied on self-reported subjective outcomes.9 10 We assessed psychiatric morbidity by using a more objective, register-based measure (hospitalisation for psychiatric disorders). Third, many of the previous studies have been conducted in restricted samples such as in specific clinical populations,9 10 15 whereas we examined the association in a large cohort of employees. Fourth, to complement earlier prospective studies with relatively short follow-ups such as 6 months,15 12 months,8 2 years16 or 5 years,7 we investigated the long-term effects of SOC by using a 19-year follow-up period.
Study setting, design and data
Data originate from the Still Working Study. This is a prospective cohort study which assesses health and potential risk factors at baseline and includes data on 19-year mortality and morbidity among private sector industrial employees within a multinational forest industry corporation based in Finland.17
In 1986, a questionnaire survey on demographics, psychosocial characteristics and health-risk behaviours was sent to all 12 173 (69% blue-collar workers, 77% male) employees of this company in Finland. Altogether 76% of the personnel (n=9282) responded. Of the respondents, 69% (n=6442) were blue-collar employees who typically worked as monitors of the machines in the industrial plants and maintenance occupations, while the white-collar employees (n=2840) were mostly employed as managers, foremen and technical staff. Seventy-eight per cent were men. Compared with the eligible population, women (22% vs 23%) and older employees (mean=40.4 years vs mean=41.0 years) were slightly over-represented among identifiable participants. The rate of psychiatric disorders was higher among the eligible population than among the participants (7% vs 4%). The study design, sample selection and description of the final study population are described in figure 1.
Information on hospital admissions for psychiatric disorders during the period between 1 March 1986 and 31 December 2005 was derived from the National Hospital Discharge Register. This register is maintained by the National Institute for Health and Welfare. Data on hospital admissions before and after the baseline survey were linked to all respondents by each participant's ID number. ID number is a unique number that all Finnish citizens are given at birth and which is used for all contacts with welfare and healthcare organisations.
In order to study the onset of new psychiatric disorders, we excluded participants with a history of hospital admissions for psychiatric disorders by baseline (n=210). Those employees who (1) were up to the survey 1 March 1986 free from psychiatric disorders (no recorded hospital admissions); (2) had worked for the company for at least 24 months before the survey; (3) responded to the scale of SOC; (4) did not have any missing values for any other study variables; and (5) were identified from the database of the National Population Register Centre were included in the final cohort of 8029 employees. The mean length of follow-up was 18 years and 9 months (range 0.0–19.8 years). At baseline, the mean age was 40 (range 18–65) years, and the average organisational tenure was 16 (range 1–49) years. The study was approved by the ethics committee of the Finnish Institute of Occupational Health.
Sense of coherence
SOC was assessed with a 13-item version of Antonovsky's Orientation to Life Questionnaire.18 The answers are provided using a seven-point response scale. The example items are as follows: ‘Most of the things you do in the future will probably be completely fascinating (meaningfulness)’; ‘Do you have the feeling that you are in an unfamiliar situation and don't know what to do?’ (comprehensibility); and ‘How often do you have the feeling that you’re not sure you can keep things under control?' (manageability) (Cronbach α=0.84). A mean score of ratings of all SOC items was constructed. Higher values indicate stronger SOC. As in some prior studies, the SOC summary score was divided into quartiles.19
Hospitalisation for psychiatric disorders
Data on all persons who were hospitalised for psychiatric disorders (yes vs no) before the assessment of SOC (1964–1986), during the assessment (in 1986) and after the assessment (1986–2005) were obtained from the Hospital Discharge Register. This national register covers information on the hospital admissions for each Finnish citizen residing in Finland.
Ascertainment of mortality
The dates and causes of death from 1 April 1986 to 31 December 2005 were obtained from the National Death Register kept by Statistics Finland. The database provides virtually complete population mortality data.
Potential confounding factors
The potential confounding factors examined were sex, age, marital status, education (elementary education, secondary education, and tertiary education), occupational status (manual vs non-manual), physical work environment (hazards: yes vs no), health behaviours and minor psychiatric morbidity, all measured at baseline. Data on sex, age and marital status (married vs not married) were obtained from the National Population Register Centre, while education, occupational status, and physical work environment were assessed with the baseline questionnaire.
Health-risk behaviours have been found to be associated with psychiatric disorders20 21 and therefore may potentially confound or mediate the relationship between SOC and psychiatric morbidity. The following health-related behaviours were measured with the baseline questionnaire: regular smoking (yes vs no); binge drinking (excessive drinking leading to intoxication twice or more/month vs less than twice/month)22 and physical activity (exercising once a week or more vs less than once a week).
Psychological distress, representing an indicator of potential undiagnosed minor psychiatric disorder, was assessed in the survey with a 10-item four-point scale measuring insomnia, overstrain, depressive symptoms, nervousness, fatigue, tension and anxiety.23 24 For descriptive purposes, a summary scale was computed and dichotomised; the respondents in the highest quartile were defined as having high psychological distress (Cronbach α=0.89). According to previous Finnish occupational cohort studies, this level of symptoms indicates moderate or severe psychological distress.25 However, to fully control the confounding impact of self-rated psychological distress, the variable was used as a continuous measure in the main analyses.
Descriptive statistics were applied to obtain means of SOC by covariates (table 1). The association between SOC and hospital admissions for psychiatric disorders was assessed using Cox proportional-hazards models. For each participant, person-days of follow-up were calculated from 1 March 1986 to death, to hospitalisation for psychiatric disorders, suicide attempt or death due to suicide, or to 31 December 2005, whichever of these three options came first. The time-dependent interaction term between predictor and logarithm of follow-up period was non-significant, confirming that the proportional hazards assumption was justified (p>0.11). To examine the relationship between SOC and psychiatric morbidity, adjusted hazard ratios (HRs) and 95% CIs for quartiles of SOC were calculated. The lowest quartile of SOC (weak SOC) was used as a reference category. The analysis was conducted in three steps. First, baseline socio-demographics were adjusted for. Second, baseline health-related behaviours were additionally adjusted for. Third, adjustment for baseline psychological distress was added. Additional analyses were conducted separately for hospital admissions for alcohol and drug-related diagnoses, for other than alcohol and drug-related diagnoses and for severe affective disorders. To guarantee a maximum number of cases in these additional analyses, events were defined using the onsets of psychiatric disorder subcategory, and only those who died were used as censored cases. The analyses were conducted with the TPHREG procedure in the SAS 9.1 statistical software package.
Of all 8029 participants with no hospital admissions for psychiatric disorders by baseline, 826 died during the follow-up and were censored at the time of death. A total of 376 participants were admitted to hospital for a psychiatric disorder (n=351) or suicide attempt (n=25), and 30 participants committed suicide after baseline (n of cases=406, 5% of the study population). For the participants who were admitted to hospital for a psychiatric disorder during the follow-up, the mean before the first admission was 9.9 years (range 0.0–19.8 years). The diagnoses according to ICD-9 categorisation are presented in table 2. The largest endpoint categories were alcohol- or drug-related psychiatric disorders and episodic mood disorders. The total number of cases of psychiatric disorders was somewhat higher, because of some other psychiatric disorders. Seven per cent of the participants (n=24) with psychiatric disorder had more than one diagnosis associated with psychiatric problems related to the same hospitalisation, while 35% of them (n=122) had a disease related to some other main disease category. The hospitalised were more often men, were non-married, were blue-collar workers, had elementary level education, were smokers, were binge drinkers, had lower physical activity and had more often experienced high psychological distress (table 1).
Table 1 shows variations in SOC mean scores by demographic and other factors. The mean of SOC in the total sample was 64.8. Men and the respondents who were married, had the highest educational and occupational level, did not have a physical work environment, were non-smokers, used less alcohol, were physically more active and had low psychological distress reported the highest mean scores.
Relationship between SOC and psychiatric disorders
As table 3 shows, after adjustment for sex, age, marital status, education, occupational status and physical work environment at baseline, a strong SOC was associated with a 52% decreased risk of hospital admission for psychiatric disorders (HR=0.48, 95% CI 0.36 to 0.64). A similar pattern in results prevailed after further adjustment for health-risk behaviours and self-rated psychological distress at baseline. The result was replicated in a subcohort of participants who did not report an elevated level of psychological distress at baseline (HR=0.59, 95% CI 0.40 to 0.86). Because undiagnosed psychiatric disorders may affect these results, a stratified analysis among employees who were alive 4 years after the SOC assessment was performed. They indicated similar associations between SOC and psychiatric disorders between 1990 and 2005 (data not shown). To summarise, in all models, the participants with a weak SOC had the shortest time before the hospital admission.
Relationship between SOC and hospital admissions by diagnosis
Table 3 also presents the relationship between SOC and hospital admissions by diagnosis. A strong SOC was associated with about 57% decreased risk of hospital admission for alcohol- and drug-related psychiatric disorders after adjustment for socio-demographics. This association was slightly attenuated after further adjustments but remained significant. However, in case of psychiatric disorders excluding substance abuse, the relationship between SOC and a decreased risk of psychiatric disorder was not observed after adjustment for baseline psychological distress. Similarly, the association between SOC and reduced hospitalisation for severe affective disorders including depression was observed only before, but not after, adjustment for baseline psychological distress.
In this prospective occupational cohort study, an initial strong SOC was associated with about a 40% lower risk of psychiatric morbidity measured as a hospital admission for a psychiatric disorder or hospital admission for a suicide attempt or death due to a suicide across 19 years. This result could not be explained by a variety of baseline socio-demographic and health behavioural variables. The association was also quite independent of baseline psychological distress, a proxy for undiagnosed mental health problems.
It seems that the relationship between SOC and psychiatric morbidity varies to some extent according to diagnosis. After adjustment for socio-demographics and health-related behaviours, a strong SOC remained a protective factor for hospital admissions for severe affective disorders including depression, the most prevalent psychiatric disorder. However, the significant relationship disappeared after further adjustment for baseline self-reported psychological distress. In contrast, the association between a strong SOC and a lower risk of hospital admissions for general psychiatric morbidity and for substance-abuse-related disorders remained significant also after this adjustment. In earlier Finnish studies, strong SOC has been associated with a reduced risk of depression,8 26 but these studies used self-reported measures of depression and did not adjust for psychological distress. On the other hand, Ristkari et al7 found an association of SOC with subsequent depression and other psychiatric disorders as recorded in military registers, after adjustment for self-reported psychopathology at baseline. In our study, the number of affective disorder cases was quite low, and this probably affected these results. Moreover, this adjustment may represent overcontrolling, as symptoms of depression and anxiety were components of our psychological distress measure.
Several processes may explain the association between SOC and psychiatric morbidity. First, common genetic or physiological processes can determine both psychological attributes, such as SOC, and the state of (mental) health.27–29 Second, because of adequate adaptive strategies, a strong SOC can buffer the impact of stressful life events on mental health.30 31 Third, individuals with a strong SOC may be more likely to engage in healthy coping behaviours, transactions with health professionals, seeking early treatment and compliance that may result in reduced severity of illness.32 In contrast, a weak SOC can facilitate health-damaging behaviours, such as smoking and sedentariness, which in turn may increase negative emotions towards the self. However, in these data, the association between a strong SOC and a decreased risk of psychiatric disorder remained, even after controlling for lifestyle risk factors. Therefore, it seems plausible that other factors are likely to underlie the relationship between SOC and the onset of psychiatric disorder. For example, individuals with a strong SOC may have larger social networks, and they may receive more social support than their counterparts with a weak SOC.33 34
SOC and mental health: overlapping constructs?
It has been argued that a very high negative correlation between SOC and mental health measures suggests that the instruments used may actually assess the same phenomenon.14 Indeed, SOC has been found to be negatively associated with anxiety, anger, burnout, demoralisation, hostility, hopelessness, perceived stressors, self-rated depression and post-traumatic stress disorder.5 35 Based on findings from confirmatory factor analysis and structural equation modelling, Eriksson and Lindström2 suggest that SOC and mental health are two independent but correlated constructs. The present study, which used register-based and self-reported measures of mental health, supports this. An earlier study7 found that as a risk factor, low SOC was more sensitive to diagnosed psychiatric disorders than to self-reported psychiatric symptoms. In the future it would be interesting to examine whether SOC is independently associated with outcomes such as mortality in these data, and to observe whether the impact of SOC varies according to the cause of mortality.
Strengths and weaknesses of the study
Our findings rely on large data on participants with no history of hospital admissions for psychiatric disorders by baseline. The results persisted after adjustment for a range of risk factors for psychiatric disorders and baseline psychological distress. Non-response occurred randomly enough to limit the potential for selection bias. Ascertainment of psychiatric morbidity was prospective and register-based. The accuracy of data on psychiatric diagnoses in the Finnish Hospital Discharge Register has been found to be excellent,36 and the linkage to records was successful for all participants. Further advantages include an exceptionally long follow-up period, which is important, since the influence of SOC on health outcomes may manifest itself over a long period of time.
The present study has some limitations that should be addressed. First, even if a long follow-up can generally be considered as strength, individuals can develop adverse health behaviours during this long time period, and they could have an impact on the eventual development of psychiatric disorder.
Second, even if participants with a history of hospital admissions for psychiatric disorders at baseline were excluded from the data, a number of employees with severe psychiatric disorders may have remained undiagnosed. Therefore, we controlled for baseline psychological distress, a proxy for undetected mental health problems. It is possible, nevertheless, that employees who died during the follow-up may have had an undetected severe psychiatric disorder which may have contributed to a risk of death. If this was the case, the effect of SOC on incidence of psychiatric disorders found in this study may have been conservatively estimated.
Third, it is possible that some unmeasured factors are behind the observed associations between SOC and psychiatric disorders. In addition, a large sample may cause type 2 errors, because it yields significant differences more easily. However, in this prospective study, a number of multivariate regression analyses offered sound evidence, and the main findings remained clear.
Fourth, it can be assumed that individuals' mental health may influence their SOC. Health represents one of the sources responsible for the maintenance of the level of SOC.32 SOC develops as a result of learning experiences that accumulate over the lifespan.14 Persistent or serious mental health problems may shape a person's daily life in terms of dimensions of SOC, and these experiences, in turn, could influence the development of SOC. A previous study found that chronic stress, if not managed properly, can result in weakened SOC.37 However, in earlier research, predictive relationships from health to SOC have not been found.3
Fifth, all participants worked for a large multinational industrial company in Finland and had a full-time job in baseline limiting the generalisability of our findings. Interestingly, epidemiological research has shown that SOC may have a direct positive impact on mental health also in non-western cultures.38 Nevertheless, the mean of SOC varies to some extent between study populations also within the same national and cultural context,26 39 and it may therefore affect the general mental health of the communities. In our sample, the mean of SOC was not particularly high.
Sixth, the rate of psychiatric beds declined in Finland during the follow-up40 (more than two beds per 1000 persons in the 1980s, fewer than one bed per 1000 persons in the 2000s). It is therefore likely that during the later part of the follow-up, more severe mental-health problems occupied a more salient role in the spectrum of psychiatric disorders, while less severe problems were treated using drugs and consulting other types of health services. This may have influenced the sensitivity of our mental health indicator.
The results from a 19-year follow-up support the protective role of strong SOC in relation to both substance abuse and non-substance-abuse-related psychiatric disorders. These findings suggest that poor SOC may represent a risk marker for psychiatric disorders. Antonovsky32 indicated that SOC could be modestly improved to benefit individuals. SOC has previously been implemented in behavioural health services by generating empowering dialogues to foster the strengths of individuals.41 It has been suggested that SOC can be enhanced with individual level interventions, such as with a mode of therapy42 or a stress-reduction programme.43 Moreover, as it has been shown that certain work characteristics might affect SOC,44 workplace interventions could be useful tools in efforts to strengthen SOC and promote good mental health.
What is already known on this subject
Earlier studies have shown the relationship between sense of coherence (SOC) and mental health.
However, prior evidence is mainly based on self-reports, short follow-ups and small or specific study samples.
What this study adds
The results from this 19-year follow-up study support the protective role of strong SOC in relation to both substance abuse and non-substance-abuse-related psychiatric disorders.
Poor SOC may represent an early risk marker for psychiatric disorders.
Funding The study was supported by grants from the Academy of Finland (project 110451) and the Finnish Work Environment Fund (project 106417; AV). MK, JV (projects 117604, 124271 and 124322) and AV (project 128089) were also supported by the Academy of Finland.
Competing interests None.
Ethics approval Ethics approval was provided by the Ethics Committee of the Finnish Institute of Occupational Health.
Provenance and peer review Not commissioned; externally peer reviewed.