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Stability of Sleep Timing against the Melatonin Secretion Rhythm with Advancing Age: Clinical Implications

Department of Neuropsychiatry, Akita University School of Medicine 1-1-1 Hondo, Akita City, Akita 010-8543, Japan

Address all correspondence and requests for reprints to: Kazuo Mishima, M.D., Department of Neuropsychiatry, Akita University School of Medicine 1-1-1 Hondo, Akita City, Akita 010-8543, Japan. E-mail: mishima{at}psy.med.akita-u.ac.jp.

Aging is often associated with decreased ability of sleep maintenance. It has been hypothesized that the elderly experience a delayed timing of sleep period relative to the circadian phase of various sleep-promoting physiological functions, possibly causing decreased sleep propensity in the latter part of their nocturnal sleep. We evaluated the relationship between the sleep timing and circadian phase of melatonin secretion, which is known as a possible human sleep modulator as well as a stable marker of biological clock phase (BCP). Actigraph sleep recordings were performed, followed by the evaluation of melatonin phase under dim light in 42 healthy elderly volunteers (mean age, 68.8 yr; male/female ratio, 16/26) and 27 healthy young male volunteers (22.5 yr). Elderly subjects showed remarkable clock time advances in both the midpoint of BCP and sleep timing, with a significant decrease in sleep maintenance ability. However, they showed no significant age-related changes in the sleep timing against the midpoint of BCP, suggesting that early morning awakening in the elderly appeared in a BCP for which sleep propensity remained sufficient to sustain sleep. The present findings do not support the hitherto known hypothesis that age-related delay in the sleep timing against the BCP induces the deterioration in sleep maintenance in the elderly.

This work was supported by Special Coordination Funds of the Ministry of Education, Culture, Sports, and Technology and a Grant-in-Aid for Cooperative Research from the Ministry of Health, Labor, and Welfare of Japan.

Abbreviations: AUC, Area under the curve; AUC_half, area under the curve for the second half of sleep time; BCP, biological clock phase; BT, body temperature; DLMOff, dim light melatonin offset time; DLMOn, dim light melatonin onset time; mBCP, midpoint of biological clock phase; MLT, melatonin; SCN, suprachiasmatic nucleus; SE, sleep efficiency; WASO, wake time after sleep onset.