Daily melatonin intake resets circadian rhythms of a sighted man with non-24-hour sleep-wake syndrome who lacks the nocturnal melatonin rise.

Effects of daily melatonin intake on the circadian rhythms of sleep and wakefulness, rectal temperature and plasma cortisol were examined in a sighted man who had suffered from the non-24-hour sleep-wake syndrome. The subject lacked the nocturnal melatonin rise in plasma, but showed robust circadian rhythms in rectal temperature and plasma cortisol. The sleep-wake rhythm free-ran with a period longer than 24 hours. Daily melatonin intake at 21:00 h concentrated sleep episodes in the nocturnal period (24:00-8:00 h), and increased the length of the episodes. A single oral dose (3 mg) of melatonin increased plasma melatonin levels to about 1300 pg/mL within one hour and remained at pharmacological levels for approximately 6 hours. The trough of rectal temperature and the circadian rise of plasma cortisol were fixed to the early morning. A higher dose of melatonin (6 mg) did not improve the general feature. After the cessation of melatonin intake, the sleep-wake rhythm began to free-run together with the circadian rhythms in rectal temperature and plasma cortisol. It is concluded that daily intake of melatonin at early night time resets the circadian rhythms in a sighted man who lacked the nocturnal melatonin rise and showed free-running circadian rhythms in routine life.