A biological night in long sleepers and in short sleepers

Leo Sher, M.D.

Fifteen years ago, our paper, “A longer biological night in long sleepers than in short sleepers” was published in the Journal of Clinical Endocrinology and Metabolism (1). We examined whether individual differences in sleep duration are associated with systematic differences in the duration of the biological night that is programmed by the circadian pacemaker and reflected in the nocturnal interval of circadian rhythms in neuroendocrine function, body temperature, and arousal.

Young, healthy long sleepers (sleep duration >9 h) and short sleepers (<6 h) were studied under constant environmental conditions and in the absence of sleep. Two- to four-week sleep logs and wrist motor activity recordings were used to identify individuals who met the criteria

The nocturnal intervals of high plasma melatonin levels, increasing cortisol levels, low body temperature, and increasing sleepiness were longer in long sleepers than in short sleepers. The maxima in cortisol levels and sleepiness showed a close relationship to habitual wake-up time, which occurred approximately 2.5 hours later in long sleepers than in short sleepers. All four markers of the biological night (i.e., plasma melatonin levels, cortisol levels, body temperature, and sleepiness) indicated that its longer duration in the long sleepers was due to a delayed offset in the morning and not an advanced onset in the evening.

The results of this study indicate that the circadian pacemaker programs a longer biological night in long sleepers than in short sleepers. It appears that individual differences in the circadian pacemaker’s program may contribute to the variability of sleep duration in the general population

In 2004, the authors of this paper received an International Award for this publication. Daniel Aeschbach, Ph.D., Leo Sher, M.D., Teodor T. Postolache, M.D., Jeffery R. Matthews, M.D., Michael A. Jackson, M.S. and Thomas A. Wehr, M.D. received The Finalist Award of The Endocrine Society and Pfizer, Inc. International Award for Excellence in Published Clinical Research in The Journal of Clinical Endocrinology and Metabolism in 2003.

Reference

1. Aeschbach D, Sher L, Postolache TT, Matthews JR, Jackson MA, Wehr TA.  A longer biological night in long sleepers than in short sleepers. J Clin Endocrinol Metab. 2003;88(1):26-30.