Phase advance of sleep and temperature circadian rhythms in the middle years of life in humans.

Age-related changes in sleep may be linked to modifications in the circadian timing system. This study compared sleep patterns and unmasked circadian temperature parameters between a group of young subjects and a group of middle-aged subjects. Habitual bedtime and waketime were earlier in the middle-aged than in the young. In addition, middle-aged subjects reported a greater orientation toward morningness and they showed an earlier phase of temperature rhythm. No differences were found in amplitude of temperature rhythm or in habitual phase angle between sleep and the temperature rhythm. In conclusion, a phase advance of sleep and temperature circadian rhythm is already apparent in people in their forties and fifties. These changes precede modifications in amplitude or in habitual phase angle.