Two sets of mechanisms could theoretically mediate the relationship between affective states and physical health. First, positive well-being might be associated with favorable health habits and prudent lifestyles. For example, cigarette smoking is associated with psychological distress (13), and depression and anxiety are inversely related to leisure-time physical activity (14). The second possibility is that associations are mediated through psychobiological processes, defined as the pathways by which psychosocial factors stimulate biological systems through central nervous system activation of autonomic, neuroendocrine, inflammatory, and immune responses. Depressed mood has been linked with increased levels of C-reactive protein and inflammatory cytokines (15), prolonged norepinephrine responses to stress (16), and deficient immune responses after vaccination (17).
The biological correlates of positive affective states are only beginning to be described. Positive affect is associated with greater degrees of left compared with right superior frontal EEG activity at rest (18). Tugade and Fridrickson (19) demonstrated that the rate of cardiovascular recovery after stress is more rapid in individuals expressing positive emotionality. Lindfors and Lundberg (20) reported a small study involving 23 individuals in which salivary cortisol sampled every 2 h over the working day was inversely related to scores on eudaimonic psychological well-being scales. No associations were observed with urinary catecholamines or blood pressure. Psychological well-being ratings have also been positively associated with cytokine production after vaccination for influenza and hepatitis (21).
We assessed the biological correlates of positive affective states both in everyday life settings and under standardized stress testing conditions. We were interested in health-related biological indicators, so we measured cortisol during the day, ambulatory blood pressure and heart rate, and plasma fibrinogen responses to challenging behavioral tasks. Most research on affective states relies on global evaluations of positive or negative affect taken on a single occasion. The limitations of such measures for estimating subjective experience include recall bias, memory distortion, and the dominant influence of current state (22). A preferable method is momentary experience sampling, in which participants are prompted to record what they are currently feeling on several occasions for one or more days. We aggregated momentary ratings of happiness sampled repeatedly over the working day to derive a more robust estimate of positive affect than might be generated on a single occasion. We hypothesized that positive affect would be inversely associated with cortisol, ambulatory blood pressure, and heart rate, and with reduced fibrinogen stress responsiveness, independently of other factors known to influence these biological variables. A second aim of this analysis was to discover whether associations between happiness and biological responses were independent of psychological distress. Participants completed the General Health Questionnaire (GHQ), a well established screening instrument for psychiatric disorders that measures psychological distress (23), that has been found to predict coronary heart disease prospectively (24). We expected GHQ scores to be negatively associated with happiness ratings and reasoned that if positive affective states are independently related to health-related biological factors, then effects should persist after statistical control for psychological distress.