Age dierences in sleep±wake behavior under natural conditions Corrine J. Kramer a , Gerard A. Kerkhof a,b, *, Winni F. Hofman a a Department of Psychonomics, University of Amsterdam, Netherlands b Departments of Physiology (LUMC) and Psychology, University of Leiden, P.O. Box 9604, Stationsweg 46, 2300 RC Leiden, Netherlands Received 22 October 1997; received in revised form 3 December 1998; accepted 28 December 1998 Abstract Dierences in lifestyle may account for a considerable portion of the reported age-related changes in overt circadian rhythmicity. By instructing a group of healthy, noninstitutionalized, elderly subjects and a group of young adults to keep a sleep±wake log for a period of two weeks, and to wear an activity monitor for an overlapping period of 11 days, we attempted to assess age-related dierences in the habitual sleep±wake behavior, in particular its day-to-day variability. Four clusters of coherent variables were constructed, re¯ecting (1) circadian phase, (2) variability of sleep±wake behavior, (3) sleep±wake continuity and (4) subjective sleep±wake quality. The results showed that, in comparison with the young subjects, the elderly had a relatively advanced and more regular sleep±wake pattern, reported more midnight awakening and did not dier in their subjective sleep evaluation. In spite of a greater regularity in their lifestyle (which would favor a larger amplitude of the overt circadian rhythmicity) oral temperature measurements showed some evidence of a weakened 24-h periodicity in the elderly. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Human; Healthy elderly; Ageing; Circadian; Sleep±wake rhythm; Actigraphy 1. Introduction Normal aging involves several alterations in sleep±wake behavior, such as an age-related decrease of the amount of slow wave sleep, an increased number and duration of night-time Personality and Individual Dierences 27 (1999) 853±860 0191-8869/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0191-8869(99)00034-3 www.elsevier.com/locate/paid * Corresponding author. Tel.: +31-71-527-6810; fax: +31-71-527-6782.