Adjustment of the human circadian system to changes of the sleep schedule under dim light at home.

In a field study at home, eight volunteers experienced a sleep period from 01:00 to 09:00 h encompassed by dim light for 6 days, then for another 6 days they were subjected to a 3-h advance of the sleep period, and for the last 6 days they were subjected to a 3-h delay of the sleep period, i.e. they experienced again the original sleep schedule. Following the 3-h advance of the sleep period, the circadian salivary melatonin and cortisol rhythms phase advanced by about 1 h within 6 days as compared with the original rhythm profiles, following the subsequent 3-h delay of the sleep period, both rhythms phase delayed by about 1 h within 6 days and returned roughly to their original phase. The data indicate that shifting of the sleep time under dim light at home, which may occur commonly in everyday life, phase shifts the human circadian system.