Relationships between sleep stages and plasma cortisol: a single case study.

The relationship between the plasma cortisol level and sleep stages was investigated in a single male subject across 17 nights. Blood samples were taken every 30 min from 11.00 p.m. until 02.30 a.m. and every 15 min during the rest of the night. Data analyses performed for the whole nights did not give evidence for strong relations between plasma cortisol and sleep stages. Analyses on data of the second part of the night, beginning with the onset of the first cortisol peak, revealed that plasma cortisol was primarily decreasing when rapid eye movement sleep (REM) was present. Sleep stage I and periods of wakefulness were associated with increasing cortisol levels. There was no evidence for a particular EEG event triggering the first rise of plasma cortisol during the night.