Morningness-eveningness and early-morning salivary cortisol levels

The purposes of this exploratory study were: (1) to describe a 2-h segment of the early-morning salivary cortisol levels of morning (M) and evening (E) types of healthy, day-active adults on one morning; and (2) to compare selected demographic and sleep characteristics. The sample consisted of 20 subjects, aged 23-39 years, 10 of each type. Measures included: morningness-eveningness questionnaire score, demographic information, self-report sleep characteristics, and self-report of well-being. Beginning with time of arising, seven salivary samples were collected at approximately 20-min intervals. Among the sleep variables, bedtime (p = 0.005), time of mid-sleep (p = 0.002), and arising time (p = 0.043) were later in the E group as compared to the M group. Six M and one E subject awoke spontaneously on the morning of sampling without an awakening aid (p = 0.018). Even though total hours of sleep were comparable between groups, E subjects reported feeling less rested in the morning (p = 0.019). Although mean M group salivary cortisol levels were greater than mean E group levels for each sampling time, there were no significant group differences. Eight M subjects reached a sampling period salivary cortisol peak by 50 min after arising, contrasted with six E subjects who reached their peak at that time. These preliminary findings suggest that E types demonstrate lower morning arousal and a delay in their early-morning peak of salivary cortisol relative to M types. Further study is needed to explore the relationship between M and E types, their sleep-wake patterns, and cortisol secretion patterns.