FREE CORTISOL-LEVELS AFTER AWAKENING - A RELIABLE BIOLOGICAL MARKER FOR THE ASSESSMENT OF ADRENOCORTICAL ACTIVITY

In three independent studies, free cortisol levels after morning awake ning were repeatedly measured in children, adults and elderly subjects (total n=152). Cortisol was assessed by sampling saliva at 10 or 15 m inute intervals for 30-60 minutes, beginning at the time of awakening for two days (Study 1 and 2) or one (Study 3) day, respectively. In al l three studies, free cortisol levels increased by 50-75% within the f irst 30 minutes after awakening in both sexes on all days. Premenopaus al women consistently showed a stronger increase with a delayed peak a fter awakening compared to men on all days. In Study 2, there was a te ndency for lower early morning free cortisol levels for women taking o ral contraceptives (p=.10). Stability of the area under the curve (AUC ) of the early morning free cortisol levels over the three (Study 1 an d 2) or two (Study 3) days ranged between r=.39 and r=.67 (p<.001). Ne ither age, weight, nor smoking showed an effect on baseline or peak co rtisol levels. Sleep duration, time of awakening and alcohol consumpti on also appeared to be unrelated to early morning free cortisol levels . From these data we conclude that in contrast to single assessments a t fixed times, early morning cortisol levels can be a reliable biologi cal marker for the individual's adrenocortical activity when measured repeatedly with strict reference to the time of awakening.