Affective States. The sample was divided into quintiles based on happiness ratings during the working day. Participants in the lowest quintile (quintile 1) gave virtually no positive happiness ratings, whereas those in the highest quintile (quintile 5) rated themselves as happy almost all of the time (Table 1). There was no association between happiness and age, gender, marital status, or socioeconomic position. There was a positive correlation between happiness ratings on the work and leisure days (r = 0.65, P P P P = 0.004), confirming that happier individuals reported lower psychological distress (Table 1). The proportion of participants with positive GHQ case status was 29.3%, 31.8%, 31.8%, 18.6%, and 11.6% for respondents in happiness quintiles 1 to 5, respectively. The odds adjusted for age and gender of a positive GHQ case score were 3.21 (95% confidence interval 1.00-10.3) for individuals in the lowest happiness quintile, 3.56 (1.14-11.1) for quintile 2, and 3.45 (1.11-10.7) for quintile 3 compared with the highest happiness quintile. Men and women did not differ significantly in any of these analyses.
Neuroendocrine and Cardiovascular Activity in Everyday Life. Cortisol aggregated over eight samples taken at 2-h intervals on the working day averaged 7.70 ± 2.8 nmol/liter and was slightly higher in men than women (P = 0.043). Cortisol concentration differed across the happiness quintiles after controlling for age, grade of employment, smoking status, and body mass index (BMI), and this effect remained significant after the GHQ was included as a covariate (P = 0.009). Cortisol levels also decreased across the day (P Fig. 1). The mean salivary cortisol over the leisure day was 7.22 ± 3.0 nmol/liter and did not differ between men and women. The difference in leisure-day cortisol across the happiness quintiles was also significant after the GHQ and other covariates were taken into account (P = 0.026). Levels were greatest in the lowest happiness quintile (adjusted mean 8.24 ± 4.1 nmol/liter), declining to 6.17 ± 1.8 nmol/liter in the highest happiness quintile (a 34% difference). Thus on both work and leisure days, higher levels of happiness were associated with lower cortisol levels, independently of psychological distress and other covariates.
Happiness was not associated with ambulatory blood pressure in this study. Transient episodes of activation stimulated by positive mood states may prevent any inverse association between broader positive experience and blood pressure from becoming apparent (33). Nevertheless, in men but not women, happiness was associated with ambulatory heart rate after controlling for age, grade of employment, smoking, BMI, and physical activity (P = 0.020). This effect remained significant after additional control for GHQ scores (P = 0.033). Heart rate averaged across the working day and evening was greatest in the low happiness quintile, and was less in happier men (Fig. 1).
Mental Stress Testing. In the laboratory phase of the study, subjective stress averaged 1.45 ± 0.75 during baseline, rising to 4.04 ± 1.4 for task trials. Systolic blood pressure averaged 114.6 ± 12.1 mmHg (1 mmHg = 133 Pa) during baseline, increasing to 140.9 ± 21.1 mmHg during task trials, whereas diastolic blood pressure rose from 70.1 ± 9.6 to 83.7 ± 11.4 mmHg. There were no differences across happiness quintiles in subjective stress, blood pressure, or heart rate responses to tasks, and ratings of task difficulty and controllability were also unrelated to happiness group.
Plasma fibrinogen concentration in blood drawn during the baseline averaged 2.87 ± 0.6 g/liter and was unrelated to happiness. Fibrinogen concentration increased after stress, and there were significant differences in stress responses across happiness quintiles after covarying for age, gender, grade of employment, smoking, BMI, and baseline fibrinogen (P = 0.003). Inclusion of the GHQ as an additional covariate did not change this result (P = 0.011), illustrated in Fig. 2. The increase in fibrinogen (adjusted for covariates) with stress averaged 0.12 g/liter in the lowest compared with 0.0097 g/liter in the highest happiness quintile. We found that 68.4% of participants showed an increase in fibrinogen concentration with stress, whereas there was no change or a decrease in fibrinogen between baseline and task trials in 31.6%. The odds of a stress-induced increase in fibrinogen were 3.72 (confidence interval 1.16-11.9) for participants in happiness quintile 1, adjusted for covariates including GHQ score, compared with the highest happiness quintile.