Relationship between Napping and Melatonin in the Blind

Abstract

Daytime sleepiness is a common complaint in blind subjects. Abnormally timed melatonin has been invoked as a possible cause of both daytime sleepiness and nighttime awakening. In free-running blind individuals, there is an opportunity to assess the relationship between endogenous melatonin rhythms and subjective sleepiness and naps. The aim of this study was to characterize melatonin rhythms and simultaneously to evaluate subjective napping. A total of 15 subjects with no conscious light perception (NPL) were studied for 1 month. Prior to the study, sleep disorders were assessed using the Pittsburgh Sleep Quality Index. Cosinor and regression analysis revealed that 9 of the 15 NPL subjects had free-running 6-sulphatoxymelatonin (aMT6s) rhythms (period [tau] range = 24.34 to 24.79 h), 3 were entrained with an abnormal phase, and 3 were normally entrained. Most of the subjects (13 of 15) had daytime naps; the 2 individuals who did not made conscious efforts not to do so. Subjects with abnormal aMT6s rhythms had more naps of a longer duration than did those with normal rhythms. Free-running nap rhythms occurred only in subjects with free-running aMT6s rhythms. The 2 abnormally entrained subjects who napped did so at times that coincided with high levels of aMT6s (mean aMT6s acrophase [phi] +/- SD = 14.30 +/- 1.08 h, 20.30 +/- 0.62 h; mean nap time +/- SD = 14.01 +/- 3.60 h, 18.23 +/- 3.20 h, respectively). Regardless of aMT6s rhythm abnormality, significantly more naps occurred with a 4-h period before and after the estimated aMT6s acrophase. In 4 free-running subjects, aMT6s acrophase (phi) passed through an entire 24-h period. When aMT6s was in a normal phase position (24:00 to 06:00 h), night-sleep duration tended to increase with a significant reduction in the number and duration of naps. Sleep onset and offset times tended to advance and delay as the aMT6s rhythms advanced and delayed. Our results show a striking relationship between the timing of daytime production of melatonin and the timing of daytime naps. This suggests that abnormally timed endogenous melatonin may induce sleepiness in blind subjects.

The Effects of Low-Dose 0.5-mg Melatonin on the Free-Running Circadian Rhythms of Blind Subjects

“…This subject had a small number of data points because of the subject's long τ and consequent short duration of melatonin treatment (i.e., when τ = 24.95 h, it takes only 26 days to complete one full cycle of τ and T = 24.00 h). Analysis by midrange crossing points confirmed a shortened period of 24.46 h. In addition, the timing of naps also suggests a shortened period, in that the number of days between episodes of daytime napping associated with circadian desynchrony (Lockley et al, 1997b) is increased during the melatonin treatment in this subject, suggesting a longer beat cycle consistent with a shorter period (Fig. 1c, right panel).…”

“…It is characterized by cyclic episodes of poor sleep and increased daytime napping when the circadian system is out of phase with the 24-h day (identified by aMT6s acrophase at an abnormal phase, 0600-2400 h), followed by episodes of better sleep and improved daytime alertness when the aMT6s rhythm is at a relatively normal circadian phase (2400-0600 h) (Lockley et al, 1997b. Free-running rhythms in sleep, without other endogenous circadian rhythm markers, are not always readily observed in field studies due to social factors such as the necessity to keep standard working hours.…”

“…Determining why interindividual differences exist with respect to the efficacy of entrainment by melatonin is vital to the development of melatonin administration regimes applicable to a general population in the treatment of free-running circadian rhythms and non-24-hr sleep-wake disorder (Lockley et al, 1997b. The present finding that melatonin administration can entrain some, but not all, subjects when their endogenous circadian phase "drifts" into an appropriate phase relationship with the treatment time, rather than having to initiate treatment at an appropriate phase, has the potential to make treatment regimes easier to develop.…”

Sleep and Circadian Rhythms in Hospitalized Patients with Decompensated Cirrhosis: Effect of Light Therapy

“…The Horne-Östberg (HÖ) questionnaire determines a subject's diurnal preference (definitely morning [score 70-86], moderately morning [59-69], intermediate [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58], moderately evening [31][32][33][34][35][36][37][38][39][40][41] and definitely evening [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]) based on 19 self-administered questions [24].…”

Effects of light on human circadian rhythms

“…L'estimation de l'inhibition de la sécrétion de mélatonine induite par la lumière indique que la réponse dépend de l'intensité et de la longueur d'onde. Contrairement à l'exposition oculaire à la lumière, la lumière extra-oculaire n'induit pas de [2,3,10,16,24,29,33], cortisol [5, 11, 13, 23-26, 29, 36], core body temperature [10,24,34] and the sleep/wake cycle [14,21,22,24] [ 18,20].…”