Empirical evidence suggests that there are marked associations between positive psychological states and health outcomes, including reduced cardiovascular disease risk and increased resistance to infection. These observations have stimulated the investigation of behavioral and biological processes that might mediate protective effects. Evidence linking positive affect with health behaviors has been mixed, though recent cross-cultural research has documented associations with exercising regularly, not smoking, and prudent diet. At the biological level, cortisol output has been consistently shown to be lower among individuals reporting positive affect, and favorable associations with heart rate, blood pressure, and inflammatory markers such as interleukin-6 have also been described. Importantly, these relationships are independent of negative affect and depressed mood, suggesting that positive affect may have distinctive biological correlates that can benefit health. At the same time, positive affect is associated with protective psychosocial factors such as greater social connectedness, perceived social support, optimism, and preference for adaptive coping responses. Positive affect may be part of a broader profile of psychosocial resilience that reduces risk of adverse physical health outcomes.

There is growing evidence that positive psychological well-being is associated with reduced risk of physical illness and prolonged survival. In one sense this is not surprising, because serious illness frequently leads to deterioration in mood or sense of vitality. The intriguing issue is whether psychological well-being protects against future illness or inhibits the progression of chronic disease. Central to this research is the question of whether positive psychological factors simply reflect the absence of depression, anxiety, and other negative states or contribute independently to health outcomes. Depression, stress, and anxiety are known to be associated with health impairment and increased risk for a variety of physical illnesses (Steptoe, 2006b), but there is growing evidence that the effects of positive affect may be present even after depression and anxiety are taken into account.

The first aim of this article is to outline the evidence that positive affect and other positive dispositions predict future health. A variety of different terms have been used to describe positive states and traits in the literature, including happiness, positive affective style, and emotional vitality (Lyubomirsky, King, & Diener, 2005). These are in turn related to traits such as hopefulness, cheerfulness, and life satisfaction. Although there may be important distinctions between these characteristics in terms of their duration and developmental antecedents, in practice there is considerable overlap between the constructs (Kashdan, Biswas-Diener, & King, 2008), and their associations with health outcomes are closely correlated. The present article therefore addresses a broad range of positive affective states and dispositions. Second, we address the behavioral and biological pathways through which such effects may be mediated, highlighting recent research carried out by our group. We have placed particular emphasis on assessments of positive affect made using ecological momentary assessment (EMA) techniques, because these relate to everyday life experiences that may be particularly relevant to concepts of resilience in ordinary life. Third, we position this research in the broader context of protective psychosocial factors that have been identified as relevant to physical health outcomes. We conclude by addressing the question of whether positive affect is likely to make an independent contribution to disease prevention or whether it is a summary indicator of other protective and resilience factors such social connectedness, social support, adaptive coping and high-esteem

POSITIVE AFFECT AND PHYSICAL HEALTH

The research literature relating positive affect and psychological well-being with physical health is growing (Howell, Kern, & Lyubomirsky, 2007; Pressman & Cohen, 2005; Veenhoven, 2008). The strongest research design definitively to establish causality is the experimental study, in which participants are assigned at random to different levels of positive affect and tracked for health outcomes. In its pure form, such a design is rarely feasible or ethical, but a small number of quasi-experimental studies have been conducted. Notably, S. Cohen, Doyle, Turner, Alper, and Skoner (2003) and S. Cohen, Alper, Doyle, Treanor, and Turner (2006) have used experimental exposure to infectious organisms such as rhinovirus (common cold) and influenza virus and analyzed responses to the virus in relation to emotional state. In these studies, volunteers were administered standard doses of virus and monitored in quarantine for the development of objective illness. Participants with a more positive emotional style (those whose affect remained very positive over several days) had reduced risk of developing upper respiratory illness (S. Cohen et al., 2006). Interestingly, these effects were independent of optimism, extraversion, self-esteem, and purpose in life, suggesting a rather specific association between positive affect and health outcome.

The strongest population-based research design for studying factors predicting the development of physical illness is the prospective epidemiological cohort study. This involves recruiting a large sample of initially healthy individuals, assessing positive well-being (along with traditional risk factors for disease), then tracking the cohort over several years. The relationship between positive psychological factors and future illness can then be investigated. Central to such design is as complete a census of participants as possible, because loss to follow-up may distort the results, as well as adequate assessment of potential confounders. For example, positive well-being could be associated with higher socioeconomic status (SES) or cigarette smoking, both of which contribute to health risk.

Kubzansky and Thurston’s (2007) recent study of emotional vitality and coronary heart disease (CHD) illustrates this method. A cohort of 6,025 men and women aged 25–75 years who were free of CHD at baseline were followed for an average 15 years. Over this period, 1,141 developed CHD. A measure of “emotional vitality,” an amalgam of vitality (sense of energy and pep), positive well-being (happiness and life satisfaction), and emotional self-control (feeling emotionally stable and secure), was derived from the Gene