Given the multidimensional nature of health, the literature assessing the link between health and subjective wellbeing has focused on different health outcomes (Howell et al.
2007). In a review of the literature, Pressman and Cohen (
2005) distinguish among studies examining the effect of subjective wellbeing on “longevity”, “morbidity”, “survival”, “self-assessed health status” and “severity of diseases”. Even the very perception of pain may be influenced by emotional style.
A common finding in the scientific literature analysing the link between subjective wellbeing and physical health is that the positive effect of subjective wellbeing and positive emotions is independent from the harming effects of negative emotions. For example, in an analysis on mortality carried out by Steptoe et al. (
2015), the positive effect of positive indicators of subjective wellbeing on health is confirmed even after controlling for symptoms of depression. This result is supported also by the work by Mukuria et al. (
2015) which analyse and compare several subjective wellbeing measures (looking at both single items and composite scales) using correlations and factor analysis. Mukuria et al. find a strong correlation between different subjective wellbeing measures, this being higher among positive measures. Their results from factor analysis suggest that positive and negative items are linked to different latent constructs, which are only weakly correlated. This suggests that positive and negative emotions are not simply “the opposite ends of a continuum” (Cohen et al.
2003, p. 652) and therefore can have an independent effect from each other.
3.1.1 Mechanisms Explaining the Health-Happiness Linkage
With regards to the mechanisms through which subjective wellbeing can affect health, the literature has identified several possible pathways (Ong
2010).
2 First, it has been shown that individuals with higher levels of subjective wellbeing are more likely to have a healthier lifestyle. Higher life satisfaction levels are found to be associated with not smoking, doing more physical exercise, using solar screen and eating healthy (Grant et al.
2009), improvements in sleep quality (Steptoe et al.
2008; Cohen et al.
2003), and higher adherence to treatment regimes (Pressman and Cohen
2005, p. 957).
The second mechanism explaining the effect of subjective wellbeing on health is represented by the biological and physiological responses of the human body to life satisfaction. Some studies have found evidence that higher levels of happiness are associated with lower levels of cortisol (Cohen et al.
2003), and, more generally, with better neuroendocrine, inflammatory, and cardiovascular responses (Steptoe et al.
2005) which can increase resistance to illness (Ong
2010).
Third, a psychological pathway also exists. Fredrickson and Levenson (
1998) and Fredrickson et al. (
2000) suggest that positive emotions can offset (“undo”) the negative reactions generated by negative emotions. Furthermore, Fredrickson (
2001, p. 10) suggests that positive emotions can help people increasing their “personal resources” and “psychological resilience” with long-term effects on a number of life outcomes.
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In the following we will review studies focusing on the effect of subjective wellbeing on mortality, health behaviours, prevention of new diseases, and survival from serious illnesses.
3.1.2 Mortality
A large part of the literature has analysed the link between subjective wellbeing and mortality, with happier people being found to live longer. However, it is difficult to generalize these results, as they come from studies carried out using different wellbeing measures, statistical techniques, as well as focusing on different populations (Veenhoven
2008; Diener and Chan
2011).
In a recent review of this literature, Diener and Chan (
2011) quantify the effect of subjective wellbeing on mortality in 4–10 additional life years, when comparing individuals with high levels of subjective wellbeing with people with low levels. Diener and Chan also report the results of a meta-analysis carried out by Howell et al. (
2007), suggesting a 6-year difference in longevity for individuals with two standard deviation difference in subjective wellbeing.
It is important to stress the fact that in examining this relationship, most of these studies have taken into account also the individuals’ health practices, such as physical exercise, smoking and drinking habits. This demonstrates that happiness affects health directly, not only via a healthier lifestyle.
A particularly interesting result emerging from this literature is that the protective effect of happiness is particularly felt by the elderlies—although it should be pointed out that some studies have shown the importance of happiness on mortality also for the general adult population (e.g. Lawrence et al.
2015).
In two distinct follow up studies using data for the US (Moskowitz et al.
2008) and Germany (Wiest et al.
2011), positive affect is found to significantly decreases risk of death among individuals aged over 65, even controlling for negative affect and lifestyle. The results of these two studies also suggest that for younger adults the relationship between subjective wellbeing and mortality is mainly mediated by physical exercise (with happier individuals living longer thanks to higher levels of physical exercise).
Along these lines, other studies have measured the impact of subjective wellbeing on mortality risks among elderlies. Steptoe et al. (
2015) use ELSA (English Longitudinal Survey for Ageing) data on elderlies and show a 30% lower risk of death for the highest respect to the lowest subjective wellbeing quartile over a 8-year period. Similarly, Steptoe and Wardle (
2011) find a 35% lower risk of death using the ELSA sub-sample that completed the Ecological Momentary Assessment on the day before the survey. This has the clear advantage of having several “real-time” assessments of emotional states, rather than only a recollective one.
Ostir et al. (
2000) analyse a sample of Mexican–American aged 65–99 followed over a 2-year period finding that a high positive affect score reduces mortality risk, this being only partially mediated by medical conditions at baseline.
Some studies also show a stronger association between subjective wellbeing and mortality among healthy individuals than among non-healthy. As suggested by Veenhoven (
2008), “happiness does not cure illness but it does protect against becoming ill” (p. 449). Among others, Xu and Roberts (
2010) examine longitudinal data for the Alameda County in California showing that an increase in subjective wellbeing (measured using several indicators) is associated with lower mortality, this association being much stronger among healthy individuals than among the non-healthy.
An interesting line of research focuses on how the eudemonic dimension of subjective wellbeing, i.e. sense of life purpose, can have an effect on health outcomes and mortality. These studies typically use longitudinal data in order to link these outcomes to previous life purpose as well as controlling for a set of confounders at baseline. In a 14-year follow-up study for the US, Hill and Turiano (
2014) find that life purpose is associated with a significantly lower risk of death (0.85 hazard ratio), even controlling for other affective indicators of wellbeing. This confirms the suggestion that different wellbeing indicators are independent from each other. The analysis by Tanno et al. (
2009) uses data for Japan and suggests that both men and women with sense of life purpose are less likely to die from any cause as well as from cardiovascular diseases in different follow-up intervals. Koizumi et al. (
2008) find lower mortality risk from cardiovascular diseases, but only for men, in another 15-year follow-up study for Japan.
Using longitudinal data collected from elderly people in a residential care setting in Japan over a 12-year period and controlling for a set of confounders at baseline, Mori et al. (
2017) show that feeling of life’s worthwhileness halves the risk of developing disabilities hindering daily life activities. Similar conclusions are also found by Boyle et al. (
2010) using data for the US and looking at limitations in daily life activities and mobility.
3.1.3 Healthy Behaviour
As already pointed out, subjective wellbeing can result in increased exercise and healthier lifestyle, this leading to better health outcomes (Reiner et al.
2013). Several studies have analysed the relationship between subjective wellbeing and health behaviours. Grant et al. (
2009) use information collected on young adults in the International Health and Behaviour Study and find for example that higher subjective wellbeing levels are associated with higher likelihood of being non-smokers, of doing physical exercise, of using sun protection and eating more healthy. Similarly, Allgӧwer et al. (
2001) find that depression is correlated to having number of negative behaviours in a cross-country sample of university students, such as being a smoker, doing little physical activity, having poor sleeping habits and not using seat belts. The Copenhagen City Heart Study (Schnohr et al.
2005) finds a significant association between level of physical exercise (categorized as “low”, “moderate”, “high” or “joggers”) and life dissatisfaction (being not satisfied vs. being either very or somewhat satisfied), with lower probability of being dissatisfied among more active individuals. This may be related to the fact that the physiological adrenaline effect associated with physical exercise may have not only a transitory effects on subjective wellbeing and therefore last longer than the physical exercise itself.
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It should pointed out that the mechanism behind these associations is likely to be quite complicated and probably better described in terms of a simultaneous relationship between subjective wellbeing level and type of lifestyle. Such evidence is found for example in the analysis of the role played by physical activity in the risk of developing depression symptoms by Da Silva et al. (
2012).
3.1.4 Prevention of New Diseases
A number of studies have focused also on the direct effect of subjective wellbeing on the development of new diseases. Some research has assessed the link between happiness and cardiovascular diseases, such as stroke and heart attack.
Ostir et al. (
2001) analyse the link between positive and negative subjective wellbeing states and the risk of stroke over a 6-year follow-up, controlling also for blood pressure, smoking habits and BMI. Results suggest a protective effect of positive affect, while no significant effect is found for negative affect. Negative affect has instead been found to increase stroke incidence in a study by Everson et al. (
1998), showing that depressed persons (i.e. having at least 5 out of 18 symptoms of depression) are 1.5 times as likely to experience a stroke compared to non-depressed persons, after accounting for health practices and presence of other diseases.
Similar results are found in a study on the incidence of ischemic heart disease (IHD), showing that depressed subjects have 1.6 times the risk of experiencing nonfatal IHD and 1.5 times the risk of experiencing fatal IHD compared to subjects with no depression (Anda et al.
1993).
Some research has also analysed the link between subjective wellbeing during pregnancy and birth outcome, finding that prenatal depression is associated with premature birth (Orr et al.
2002), lower birthweight, alterations in the newborn’s biochemical and physiological profile (Field et al.
2006), as well as live birth delivery and multiple gestation in case of IVF (Klonoff-Cohen et al.
2001).
In a well-known experimental study by Cohen et al. (
2003), positive subjective wellbeing is found to be protective against the development of a cold, and, distinguishing between three categories of positive emotional style, a risk ratio of 2.9 is found for those in the lowest category respect to those in the highest.
3.1.5 Survival
The literature has also analysed the effect of subjective wellbeing on survival for people suffering from certain illnesses or chronic conditions. Pressman and Cohen (
2005) suggest that positive emotions can be beneficial for individuals affected by diseases characterised by low mortality rates, while in case of advanced or more dangerous diseases, individuals with high levels of positive emotions may be too optimistic about their real chances of overcoming the illness, this leading to lower survival due to inappropriate lifestyle and lower treatment persistence.
Subjective wellbeing is found to reduce mortality and increase survival for example among patients with diabetes (Moskowitz et al.
2008) and among people with chronic conditions (Howell et al.
2007). Bush et al. (
2001) suggest that depression increases mortality after myocardial infarction. Moskowitz (
2003) also finds that positive affect reduces mortality among HIV + men. This result may be mediated by better care and higher adherence and persistence to antiretroviral therapy in patients with higher positive affect (Carrico and Moskowitz
2014).