https://orcid.org/0000-0002-8718-1654
Abstract
Objectives
The main objective of the current study was to investigate associations between two aspects of well-being – satisfaction with life and vitality – and incidence of and mortality from ischemic heart disease. Study design. The Copenhagen Aging and Midlife Biobank (CAMB) was conducted from 2009 to 2011 and was used as baseline data with 6750 individuals having complete information on The Satisfaction with Life Scale (SWLS) and 6652 individuals with complete information on the Short Form Health Survey (SF-36) vitality scale. Incidence of and mortality from ischemic heart disease were assessed using Danish register data and a total of 349 CAMB individuals were registered with either a diagnosis (n = 337) or had died (n = 12) from ischemic heart disease before the end of follow-up (31 December 2017). The hazard ratios of ischemic heart disease according to satisfaction with life and vitality scores were investigated using Cox proportional hazard regression adjusted for potential covariates. Results. A one standard deviation increase on the SWLS was associated with an 18% reduced risk of ischemic heart disease while a one standard deviation increase on the SF-36 vitality scale was associated with a 24% reduced risk of ischemic heart disease after adjustment for baseline socio-demographic factors. These associations remained when separately adjusting for lifestyle, objective health, and social factors, but became non-significant when adjusting for self-reported health. Conclusion. Our study indicates that both psychological and health-related components of wellbeing are important in relation to ischemic heart disease.
Introduction
In 2015, ischemic heart disease (IHD), also called coronary heart disease (CHD), affected 110 million people worldwide and resulted in 8.9 million deaths, making IHD the most common cause of death globally [Citation1,Citation2]. Research aiming at identifying individuals with an increased risk of developing IHD is therefore continually of great importance.
It is well established that both genetics [Citation3] and a broad range of lifestyle factors are associated with the risk of IHD, including smoking [Citation4], physical inactivity [Citation5], overweight [Citation6] and type-2 diabetes [Citation4,Citation7]. In addition, there is solid evidence that psychological factors are potential risk factors. While the majority of this research has proposed negative psychological characteristics such as depression [Citation8–11], stress [Citation12] and hostility [Citation13] as risk factors for IHD, a growing body of research has investigated the potential protective role of positive psychological characteristics [Citation14–16]. Thus, life enjoyment has been found to be associated with reduced risk of cardiovascular disease (CVD) incidence and mortality among men but not among women [Citation17], while poor quality of life has been found to be associated with a higher risk of IHD among women but not among men [Citation18]. Furthermore, a recent Italian study found that both physical and mental health-related quality of life were associated with reduced short-term risk (<5 years) of developing CVD [Citation19]. Thus, overall there is evidence suggesting that general psychological wellbeing and positive affectivity are associated with a reduced risk of IHD [Citation14,Citation16], though results are somewhat inconsistent regarding differences between men and women (possibly due to different study samples, designs, and operationalizations of wellbeing). Also, it remains unclear what aspects of psychological wellbeing are protective of later IHD.
Satisfaction with life and vitality are two key aspects of psychological wellbeing that both consistently have been associated with physical health including heart disease. More specifically, satisfaction with life has been suggested to protect against illness in general [Citation20], to predict a reduced risk of all-cause mortality [Citation21] and mortality from CVD in healthy populations [Citation22]. Furthermore, reduced levels of satisfaction with life and vitality have been observed among individuals with IHD [Citation23,Citation24] and health-related quality of life (including a vitality scale) has been associated with other IHD risk factors such as smoking and having a history of heart disease [Citation25]. Only a few prospective studies have investigated associations of satisfaction with life and vitality with the risk of IHD [Citation14] and these studies have suggested that both satisfaction with life [Citation26] and vitality [Citation27] were protective of IHD among men and women. Furthermore, studies investigating the relative importance of satisfaction with life and vitality, for later development of IHD are currently lacking and especially studies that adjust for a range of behavioral factors, social factors, and health factors including solid objective and subjective measures are scarce. Such studies would contribute with further knowledge of the relative protective influence of different aspects of psychological wellbeing for IHD.
The main aim of this study, therefore, was to prospectively investigate associations of satisfaction with life and vitality (measured using two reliable and well-validated measures) with IHD among a large Danish community sample followed over eight years. Satisfaction with life has been defined as a cognitive process in which individuals evaluate their lives as a whole based on their own set of criteria [Citation28], while vitality refers to the presence of energy and absence of fatigue. It may be argued that while satisfaction with life reflects a general evaluation of life, vitality comprises a larger somatic component and may be more closely related to an individual’s health functioning [Citation29]. Based on the existing literature, we expected that higher satisfaction with life and higher vitality was associated with reduced risk of IHD incidence and mortality with vitality being the more important wellbeing factor for IHD.
Methods
Study sample
The present study consisted of participants from The Copenhagen Aging and Midlife Biobank (CAMB) [Citation30]. CAMB is a follow-up study of three different birth cohorts; “the Copenhagen Perinatal Cohort”, “the Metropolit 1953 Danish male birth cohort” and “the Danish Longitudinal Study on Work, Unemployment and Health”. From these three birth cohorts, 17,936 members were invited to participate in the CAMB study, which consisted of a clinical examination and a comprehensive questionnaire and was conducted from 2009 to 2011. Written consent was collected for all participants prior to examination. A total of 7243 individuals participated in CAMB corresponding to a participation rate of 40.4%. Participants who had an IHD diagnosis prior to baseline assessment (n = 360) were excluded from the study. Thus, the current study sample included the 6750 participants who had complete information on the satisfaction with life scale and sex and the 6652 participants who had complete information on the vitality scale and sex. The mean age of the study sample was 54.45 years (3.88).
Measures
Outcome
Ischemic heart disease (IHD)
Information on the incidence of IHD was derived from the Danish National Patient Register, where all patient contacts at Danish hospitals are registered since 1977. We defined IHD diagnoses as ICD-8 codes 410–414 and ICD-10 codes I20–I25. Furthermore, the Danish Cause of Death Register was used to obtain information about mortality from IHD and a combined variable indicating either IHD incidence or mortality was constructed and used as an outcome in all analyses. The end of follow-up was 31 December 2017.
Predictors
Satisfaction with life
Satisfaction with life was measured using the Satisfaction with Life Scale (SWLS) [Citation31], which was applied as part of the CAMB questionnaire. SWLS consists of five statements (e.g. “I am satisfied with my life”) with response options on a Likert scale from 1 (“strongly disagree”) to 7 (“strongly agree”). The scores are summed to a total SWLS score ranging from 5 to 35 with higher scores indicating higher satisfaction with life. For the analyses in the current study, the SWLS was transformed to range from 0 to 30. Cronbach’s alpha for the five SWLS items was 0.91.
Vitality
Vitality was measured using the vitality subscale of the Danish version of the Short-Form Health Survey (SF-36) [Citation32]. SF-36 vitality was assessed with four questions on energy and fatigue (e.g. “How much of the time during the past 4 weeks did you feel full of pep?”). The four items are answered on a Likert scale from 1 (“all of the time”) to 6 (“none of the time”). The raw sum-score was transformed to a total score ranging from 0–100 with higher scores indicating higher vitality. Cronbach’s alpha for the four SF-36 vitality items was 0.88.
Covariates
Socio-demographic factors
We obtained information on the age and sex of the participants. Furthermore, using self-reported information on school education and vocational training, a continuous variable ranging from 8–17 years was formed to measure educational length. See Mortensen et al. [Citation33] for a more detailed description.
Lifestyle factors
Body Mass Index (BMI) was calculated based on the participant’s height and weight measured at the CAMB clinical examination or self-reported height and weight if the participant had not participated in the clinical examination. Information on smoking status (current, previously or never), weekly alcohol consumption (number of units) and weekly physical activity (0–2, 3–6, 7 or more hours) were assessed as part of the CAMB questionnaire.
Chronic diseases
We calculated the Charlson Comorbidity Index (CCI) scores based on data from the Danish National Patient Register using the revised version of the CCI outlined in Quan et al. [Citation34], which contains information on 12 chronic diseases (including cardiovascular diseases) weighted according to how they predict 1-year mortality.
Self-perceived health
Self-perceived health was assessed with a single question: “How do you perceive your general health at the moment?” as part of the CAMB questionnaire with answers ranging from 1 (excellent) to 5 (poor). The two answer categories indicating highest as well as the two answer categories indicating lowest self-perceived health were combined to construct a variable with three categories of high, moderate and low self-perceived health, which was used in the statistical analyses.
Social factors
Employment status (fulltime/self-employment, part-time/reduced hours job or unemployed/pension), partner (yes/no) and social support (a binary variable specifying having a friend to talk to when in need of support) were also assessed as part of the CAMB questionnaire and used in the statistical analyses.
Statistical analysis
Characteristics for participants with high, moderate and low SWLS were examined with Chi-square tests and analyses of variance according to the nature of the variable. Descriptive statistics are presented as mean (standard deviation) in the text.
We standardized SWLS scores and SF-36 vitality scores and generated z-scores with a mean of 0 and a standard deviation of 1. Hazard ratios (HR) with 95% confidence intervals were calculated for the standardized scores using Cox regression with age as the underlying timescale. The assumption of proportional hazards was met. Participants were followed from the CAMB examination day until 31 December 2017 or until the date of their first IHD diagnosis (n = 337), date of death from IHD (n = 12), date of all-cause death (n = 263) or date of immigration (n = 50), whichever came first. In the text, hazard ratios are presented with confidence intervals(CI) as HR(CI).
Associations of satisfaction with life and vitality with the incidence of and mortality from IHD were analyzed in four successive models: Model 1 (the basis model) adjusted for sex and years of education; Model 2 adjusted for lifestyle factors; Model 3 adjusted for chronic diseases (CCI score); Model 4 adjusted for self-perceived health; and Model 5 adjusted for social factors in addition to the basis model. Preliminary analyses showed no interaction between the measures of psychological wellbeing and sex, but as some previous studies [Citation17,Citation18] present results stratified for sex, we report results for the total sample as well as for men and women separately. We repeated the analyses with a time lag of 3 years from baseline assessment to minimize the risk of potential bias due to reverse causation caused by the inclusion of IHD incidence and mortality that occurred immediately after baseline assessment.
The level of significance was defined as α = 0.05 in all analyses.
Results
presents participant characteristics of the study population according to tertiles of SWLS. In general, compared with individuals in the lowest tertile of SWLS, individuals in the top tertile of SWLS had longer education, reported less alcohol consumption, were more frequently non-smokers, more frequently reported to have a high level of physical activity, had lower BMI, had fewer diagnoses of chronic disease, more frequently reported to have high self-perceived health, were more likely to have a partner, more frequently reported to have social support, and were more likely to currently be employed. At baseline, the mean SWLS score was 26.61 (5.59) in the total sample and did not differ between men and women while the mean SF-36 vitality score was 65.09 (19.49) with men scoring slightly higher than women. A total of 349 IHD cases (IHD incidence: 337 and mortality from IHD: 12) were registered between baseline and 31 December 2017 (286 men and 63 women), corresponding to 5.2% of the total sample (6.2% in men vs. 2.9% in women).
Table 1. Participant characteristics according to tertiles (low, moderate, high) of the SWLS score.
presents results from the Cox regression investigating associations of SWLS with hazard of IHD for the total sample and separately for men and women. Highly significant negative associations were found between SWLS and hazard of IHD in the total sample. More specifically, for every 1 standard deviation increase in SWLS, we found an HR of 0.79 (0.71; 0.87) and this association remained after adjusting for sex and education, lifestyle factors, chronic disease and social factors. However, the association between SWLS and IHD became non-significant when adjusting for self-perceived health. As indicated by the non-significant interaction between SWLS and sex, results did not differ substantially for men and women though the observed HRs were slightly lower for women (ranging from 0.70 to 0.79) than for men (from 0.81 to 0.87).
Table 2. Cox regression of associations between SWLS and IHD incidence or mortality. Standardized estimates are shown.
Results from the Cox regression investigating associations of SF-36 vitality with the hazard of IHD are presented in . Highly significant negative associations were found between SF-36 vitality and hazard of IHD in the total sample with a 1 standard deviation increase in SF-36 vitality being associated with an HR of 0.74 (0.67; 0.81) for IHD and the association remained after adjusting for sex and education, lifestyle factors, chronic disease and social factors. However, again the association was attenuated when adjusting for self-perceived health. Results did not differ between men and women. Finally, the sensitivity analyses using a 3-year time lag from baseline assessment found no noteworthy changes in the estimates that all remained significant.
Table 3. Cox regression of associations between SF-36 vitality and IHD incidence or mortality.
Discussion
Main findings
Results from the current study showed that higher satisfaction with life and vitality reduced the hazard of developing IHD during the eight-year follow-up period among middle-aged men and women. More specifically, a 1 standard deviation increase in SWLS was associated with an 18% reduced hazard of IHD, while a 1 standard deviation increase in vitality was associated with a 24% reduced hazard of IHD when adjusting for age, sex, and education. The results were not explained by confounding from other well-known risk factors including lifestyle (alcohol consumption, smoking, physical activity, BMI), chronic diseases, or social factors (having a partner, social support, work status). However, associations of satisfaction with life with IHD and vitality with IHD attenuated when adjusting for self-perceived health.
Comparison with previous research
A growing body of research has investigated the effect of positive psychological wellbeing on the incidence of IHD and overall this research is in line with the results of the current study. A large review of the literature concluded that various measures of psychological wellbeing (e.g. positive affect, optimism, quality of life, life enjoyment, and health-related quality of life) exist that protect against CVD including IHD [Citation14]. However, only a few studies have investigated the effect of satisfaction with life and vitality on IHD incidence and mortality. With regard to satisfaction with life, Boehm et al. [Citation26] investigated whether satisfaction with a life measured across seven domains (satisfaction with job, love, leisure, living standard, family, sex, self) was associated with IHD incidence and mortality in the Whitehall II cohort comprising 7956 men and women aged 39–63 years who were followed over an average of 5.42 years. They found an adjusted 12% reduced risk of IHD for every 1 standard deviation increase in satisfaction with life averaged across the seven domains, which is comparable to the effect of satisfaction with life on IHD in our study (18%). With regard to vitality, Kubzansky and Thurston [Citation27] investigated the protective role of emotional vitality (measured using the validated “General Wellbeing Schedule” [Citation35] for risk of IHD over an average of 15 years among 6025 men and women (mean age 47.5 years). The authors reported an effect of emotional vitality on the incidence of IHD with an adjusted relative risk ratio of 0.98 (0.97; 0.99) for every 1 unit increase in the emotional vitality score, corresponding to an 11% reduced risk of IHD for every 1 standard deviation increase (5.69). Thus, a substantially lower effect of emotional vitality was found in the Kubzansky and Thurston [Citation27] study compared with the observed effect of SF-36 vitality on IHD in the current study (24%). This difference may reflect the use of emotional vitality versus SF-36 vitality, as SF-36 vitality may be more closely related to health status and physical functioning. Using the SF-36 questionnaire, a recent study investigated associations between health-related quality of life and incidence of IHD in a large sample of 17102 individuals who were followed over a median of 4.2 years [Citation19]. In this study, the SF-36 vitality scale was associated with reduced risk of IHD, with individuals in the highest quartile of SF-36 vitality having a 38% reduced risk of IHD (HR: 0.62 (0.42; 0.93)) compared with individuals in the lowest quartile of SF-36 vitality. Thus, together with the findings of the current study, there seems to be convincing indications that satisfaction with life and especially SF-36 vitality are of great importance for the development of IHD.
In general, the effects of psychological well-being on the risk of IHD in men versus women are unclear. One Danish study found a larger effect among women compared with men [Citation18], another study reported larger effects for men [Citation17] while Boehm et al. [Citation26] reported that the relationship was comparable for men and women. In our study, the associations between psychological wellbeing and IHD did not differ between men and women. However, we observed a tendency towards a larger positive effect of especially satisfaction with life in women compared with men, indicated by the lower HR among women. Thus, it may be that satisfaction with life is more important for physical health in women than in men. Furthermore, associations were generally less pronounced among women in our study than among men, which probably reflect differences in statistical power.
Interpretation of the findings
Several potential pathways may explain the observed link between satisfaction with life and vitality and risk of IHD, which was found in the current study. One possible explanation is that high satisfaction with life and vitality has a direct positive effect on health. This notion is supported by consisting of findings linking positive effect and high psychological wellbeing to better immune functions, lower inflammatory levels, reduced cortisol levels, lower heart rate and lower blood pressure [Citation36,Citation37]. Thus, there is considerable evidence linking positive psychological states to physiological health outcomes that indicate cardiovascular function and are relevant for the risk of developing IHD.
Another possible explanation is that satisfaction with life and vitality has an indirect positive effect on the risk of developing IHD. Individuals high on psychological wellbeing are more likely to engage in healthy behaviors such as regular physical activity and not smoke [Citation38], which are known to be protective of IHD [Citation39]. Additionally, individuals with high well-being may more frequently engage in social activities and have greater social support, which has also shown to be protective of IHD [Citation40,Citation41]. An indirect explanation mediated by health behaviors is supported by our descriptive results finding marked differences in lifestyle and social factors between participants with high and low satisfaction with life (see ). However, in our study, the association between psychological wellbeing and IHD remained when adjusting for lifestyle factors as well as social factors suggesting that improved health behavior at least not fully explains the protective effect of satisfaction with life and vitality.
In the current study, self-perceived health was the only investigated confounder that substantially attenuated the associations of satisfaction with life and vitality with the risk of IHD incidence or mortality. This may reflect an overlap between the concepts of psychological wellbeing and self-perceived health as self-perceived health involves the personal perception of their own health and not solely reflects objective health status. Additionally, our results indicate that the protective effect of vitality on IHD is more pronounced than the protective effect of satisfaction with life on IHD. This may partly be explained by the fact that SF-36 vitality to a higher degree than SWLS comprises a physical component of wellbeing.
Methodological considerations
Major strengths in the present study include the prospective design, a large community-based sample comprising three cohort studies, two different self-reported measures of psychological wellbeing at baseline, extensive information on potential confounding factors and access to nationwide population-based registers of IHD diagnoses. The prospective design minimized recall bias and in addition, allowed us to investigate the possible effects on IHD over a time span of up to 8 years in a period of life when the incidence of IHD begins to increase [Citation42]. Additionally, the inclusion of two different measures of psychological wellbeing enabled us to investigate the relative importance of each measure, which has not been done in other studies. While SWLS is a purely psychological scale (satisfaction with life in general), the SF-36 vitality scale integrated a larger somatic component of energy and fatigue, and our results thus suggest that both aspects are important. Six different statistical models were investigated to account for potential confounding factors, including measures of both self-reported and objective health at baseline. However, as in all observational studies, there may have been unrecognized confounding; thus, factors such as health motivation, anger and hostility [Citation13] were not included in the analyses as the appropriate data were not available.
In Denmark, all residents have equal and free healthcare; however, we cannot exclude the possibility that individuals with early symptoms of undiagnosed heart problems at baseline had lower satisfaction with life and vitality. Thus, given the multifaceted etiology of IHD, it is possible that early-stage health problems related to this diagnosis were present but not diagnosed at baseline and that the results partly reflect reverse causation. However, inserting a time lag of three years did not change the results noteworthily and neither did adjustment for baseline objective health, which indicates that reverse causation was not a substantial problem in this study.
A limitation is the relatively low participation rate in CAMB (40.4%) which may have resulted in selection bias. For example, it is likely that participants and non-participants differ with regard to the level of education and general health [Citation30] with mainly the most resourceful with higher psychological wellbeing having participated in CAMB. Additionally, as register information was available for both participants and non-participants, we know that there was a slightly higher rate of IHD incidence and mortality among non-participants (5.9% versus 5.2%). Thus, the effect of psychological well-being on IHD may possibly have been underestimated in the current study.
The study did not have sufficient power for analyses of subgroups of IHD diagnoses. However, as IHD includes several diagnosis codes in ICD-10, separate analyses for subgroups of diagnoses should optimally be conducted to evaluate potential differences in associations for each of the psychological wellbeing measures. Finally, all members of the included cohorts were in their midlife years at baseline and thus it is uncertain whether the current results can be generalized to other age groups or beyond the Danish population.
In summary, there is a growing interest in investigating the influence of positive psychological constructs on the risk for developing IHD. The current study contributes to this literature by emphasizing the importance of two different aspects of psychological wellbeing – satisfaction with life and vitality, with vitality exerting the largest effect on IHD incidence or mortality. Future studies should investigate whether interventions aimed to improve specific aspects of psychological wellbeing may reduce the risk of IHD.
Acknowledgments
The authors thank Kirsten Avlund, Helle Bruunsgaard, Nils-Erik Fiehn, Ase Marie Hansen, Poul Holm-Pedersen, Rikke Lund, Erik Lykke Mortensen, and Merete Osler who initiated and established the Copenhagen Aging and Midlife Biobank from 2009 to 2011. They also thank the staff at the Institute of Public Health, University of Copenhagen and the National Research Center for the Working Environment who undertook the CAMB data collection.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
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