RECOVERY OF CIRCADIAN-RHYTHM OF PLASMA-CORTISOL LEVELS AFTER A 3-DAY TRIP BETWEEN TOKYO AND SAN-FRANCISCO

The objective of the present study is to investigate the change in the circadian rhythm of plasma cortisol levels following a 3-d trip and a westbound return flight from San Francisco (SFO) to Tokyo. Six healthy male students volunteered for the project. Plasma cortisol levels were monitored 4 times daily for 13 d during the experimental period. In Tokyo, the baseline pattern of cortisol concentrations showed the classical diurnal profile. During the 50-h stay in SFO, phase advancement of 8 h was observed for the initial 32 h. This was followed by a disturbance in the profile for the remaining 18-h period. After returning to Tokyo, the subjects exhibited the original diurnal pattern beginning Day 1. However, complete resynchronization was not apparent until Day 4 after the return.