Melatonin and Cortisol assessment of circadian shifts in astronauts before flight

Melatonin and Cortisol were measured in saliva and urine samples to assess the effectiveness of a 7‐day protocol combining bright‐light exposure with sleep shifting in eliciting a 12‐hr phase‐shift delay in eight U.S. Space Shuttle astronauts before launch. Baseline acrophases for 15 control subjects with normal sleep‐wake cycles were as follows: Cortisol (saliva) at 0700 (0730 in urine); melatonin (saliva) at 0130 (6‐hydroxymelatonin sulfate at 0230 in urine). Acrophases of the astronaut group fell within 2.5 hr of these values before the treatment protocols were begun. During the bright‐light and sleep‐shifting treatments, both absolute melatonin production and melatonin rhythmicity were diminished during the first 3 treatment days; total daily Cortisol levels remained constant throughout the treatment. By the fourth to sixth day of the 7‐day protocol, seven of the eight crew members showed phase delays in all four measures that fell within 2 hr of the expected 11‐ to 12‐hr shift. Although Cortisol and melatonin rhythms each corresponded with the phase shift, the rhythms in these two hormones did not correspond with each other during the transition.