Chronotype and diurnal cortisol profile in working women: differences between work and leisure days.

The influence of chronotype on the diurnal profile of salivary cortisol was examined in a sample of 187 healthy women: 21 evening chronotype, 24 morning chronotype and 142 intermediate chronotype. Saliva samples were collected at waking, 30 min post-awakening, at 1000 h, 1200 h, 1500 h, 1700 h and at bedtime on one work and one leisure day. Several components of the diurnal profile were examined including the cortisol awakening response, the total cortisol output and the diurnal profile on both the work and the leisure day, a significant main effect of time emerged (both p<0.01). After adjustment for age, smoking status, self-rated health, time of waking, and sleep problems, no effect of chronotype was evident for cortisol in the evening, the cortisol awakening response, or total cortisol output over the working day. However, on the leisure day, total cortisol output was greater in evening-types than intermediate or morning-types, after adjustment for covariates (p=0.029). The present data indicate that chronotype has a limited impact on the diurnal cortisol profile of healthy women, and may be somewhat impervious to individual preferences for morning or evening activity.