The results summarized in this paragraph include all missions. The melatonin and cortisol cycles of the astronauts who changed sleep times gradually shifted by seven to twelve hours and the cycles of those who changed sleep times abruptly shifted by 11 to 15 hours. The melatonin rhythm of those who changed sleep times gradually shifted more gradually than that of those who made the change abruptly. Cortisol peaks were in phase with melatonin peaks in all astronauts but one, who had changed sleep times gradually. Melatonin peaks were diminished during the first four days of bright-light exposure, but had recovered by the end of the seven-day treatment period. In the expanded tests, Actillume measurements showed that ambient light in the Shuttle cabin was much lower than ambient light on the ground and that sleep quality was poor before the flight. The results showed that a seven-day period of sleep-shifting and bright light treatment before flight can achieve the desired shift in circadian rhythms. However, the number of subjects was too small for recommendations to be made. Future studies should assess body-temperature cycles, rest-activity cycles, cognitive performance, alertness, and illumination.
Part A (STS-46, STS-47, and STS-50):
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 hours 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 crewmembers showed phase delays in all four measures that fell within 2 hours of the expected 11 to 12-hour 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.
Results for Part B and C are included in the first paragraph. Individual results for these protocols are not available.
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