Which Aspects of Morningness-Eveningness Change with Age?

JOURNAL OF BIOLOGICAL RHYTHMS, Vol. 22 No. 3, June 2007 278-280 DOI: 10.1177/0748730407301054 © 2007 Sage Publications Since the early 1970s, various pencil-and-paper questionnaires have been developed so that a number can be derived that is indicative of where an individual lies on the morningness-eveningness (M/E) continuum (e.g., Horne and Ostberg, 1976; Smith et al., 1989). Despite the documented genetic basis for M/E differences (Katzenberg et al., 1998), older subjects have generally shown higher morningness scores (more toward a “morning lark” orientation) than younger adults (Monk et al., 1991; Czeisler et al., 1992). Moreover, even over the “middle” years of life (2060 y), M/E score has been shown to increase with age, associated with changes observed in the timing and quality of sleep (Carrier et al., 1997). The aims of the present study were to explore different pathways to M/E and to ascertain whether age-related changes were different among different pathways. While it is parsimonious to conceive of M/E as being a unitary concept related simply to the phase of the endogenous circadian pacemaker, several alternative pathways to a given M/E score can be proposed. A second possible pathway relates to different relative strengths to circadian and homeostatic determinants to evening alertness. For example, relative weakness in circadian strength, which has been observed in the elderly (Monk and Kupfer, 2000), might lead to evening sleepiness (as the homeostatic drive predominates) and thus to a higher M/E score. A third possible pathway is that of age-related changes in sleep duration. As age increases, the amount of time spent asleep decreases. This loss of sleep occurs predominantly during the morning hours and leads to earlier morning wake times and an increased inability to sleep late with increased age. Such changes would themselves lead to a higher M/E score. The present analysis used information obtained from individual responses to each of the 19 questions in the Horne and Ostberg (1976) M/E instrument (HOM). Study A was concerned with 150 middle-aged and young adult subjects (20-60 y, mean 35.0 y, SD 11.2 y; 72 m, 78 f), Study B with a (nonoverlapping) sample of 106 older adults (65-93 y, mean 83.1 y, SD 4.2 y; 47 m, 59 f) and 100 younger adults (19-38 y, mean 26.9 y, SD 4.5 y; 40 m, 60 f) obtained from different contributing studies. We sought to determine 1) whether factor analysis can be used to reveal different pathways to M/E score, 2) whether different pathways have different rates of age-related increase over the young adult and middle years (20-60 y), and 3) whether such pathway differences are also observed when older adults (>60 y) are compared to younger adults (<40 y). A factor analysis performed with varimax rotation was applied to the 19 question-specific HOM responses in Study A and yielded 3 major factors. Eight questions clustered in Factor 1, 6 questions in Factor 2, and 5 questions in Factor 3 (see the appendix). Factor 1 included 4 questions that are fairly clearly related to circadian phase and 4 questions that relate to alertness, sleepiness, hunger, and ability to exercise at an early morning hour. Factor 2 included 5 questions that were directly concerned with one’s alertness/sleepiness and ability to do things in the evening hours and 1 question that seems to relate more to circadian phase. Factor 3 included 5 questions that relate (directly or indirectly) to one’s alertness in the morning (and thus ability to be LETTER