Fig. 1.

Biological correlates of happiness over the working day. (a) Mean salivary cortisol averaged during the working day in relation to happiness quintile, adjusted for gender, age, grade of employment, BMI, smoking, and psychological distress. Error bars are standard errors of the mean (SEM). Cortisol levels were inversely related to happiness (P = 0.009), and there was no gender difference in this pattern. (b) Mean heart rate averaged during the working day in relation to happiness in men (black bars) and women (hatched bars). Values are adjusted for age, grade of employment, BMI, smoking, and physical activity, and error bars are SEM. The difference across happiness quintiles was significant for men (P = 0.020) but not for women.