Melatonin improves evening napping

Melatonin as a Chronobiotic with Sleep-promoting Properties

The use of exogenous melatonin (exo-MEL) as a sleep-promoting drug has been under extensive debate due to the lack of consistency of its described effects. In this study, we conduct a systematic and comprehensive review of the literature on the chronobiotic, sleep-inducing, and overall sleep-promoting properties of exo-MEL. To this aim, we first describe the possible pharmacological mechanisms involved in the sleep-promoting properties and then report the corresponding effects of exo-MEL administration on clinical outcomes in: a) healthy subjects, b) circadian rhythm sleep disorders, c) primary insomnia. Timing of administration and doses of exo-MEL received particular attention in this work. The exo-MEL pharmacological effects are hereby interpreted in view of changes in the physiological properties and rhythmicity of endogenous melatonin. Finally, we discuss some translational implications for the personalized use of exo-MEL in the clinical practice.

Melatonergic agents influence the sleep-wake and circadian rhythms in healthy and psychiatric participants: a systematic review and meta-analysis of randomized controlled trials

Exogenous melatonergic agents are widely used to treat insomnia and sleep disturbance. Several studies have shown that they might also modulate circadian rhythms. The purpose of this systematic review and meta-analysis was to summarize current knowledge about the effects of melatonin supplements and melatonin agonists on the sleep-wake cycle as well as on the circadian rhythm of melatonin in healthy participants and in patients with psychiatric disorders. The following electronic databases were searched: EMBASE, PubMed, Web of Science, CINAHL, and Cochrane Library. Of the 12,719 articles, we finally selected 30 studies including 1294 healthy participants and 8 studies including 687 patients with psychiatric disorders. Cochrane risk of bias tool was used to assess the risk of bias. Using meta-ANOVA, studies on healthy participants showed advancing effects of melatonergic supplements and agonists on sleep-wake cycle according to dosing time and dosage, despite the fact that the original individual melatonin rhythm was within a normal range (fixed effect model standardized mean difference [95% Confidence Interval] = -0.639[-0.968 to -0.310]). In a limited number of randomized controlled trials with psychiatric patients, the findings seemed similar to those with healthy participants, despite the psychiatric disorders and treatment related factors affecting circadian rhythms. Given the unmet clinical need for evidence-based treatments to correct circadian rhythms in psychiatric disorders, efficacy of melatonergic agents seen in healthy participants, and similarity of findings among psychiatric patients, large scale, well-designed randomized controlled trials are needed to test efficacy on circadian parameters in psychiatric disorders.

Melatonin ingestion after exhaustive late-evening exercise improves sleep quality and quantity, and short-term performances in teenage athletes

The present study aimed to explore the effects of a single 10-mg dose of melatonin (MEL) administration after exhaustive late-evening exercise on sleep quality and quantity, and short-term physical and cognitive performances in healthy teenagers. Ten male adolescent athletes (mean ± SD, age = 15.4 ± 0.3 years, body-mass = 60.68 ± 5.7 kg, height = 167.9 ± 6.9 cm and BMI = 21.21 ± 2.5) performed two test sessions separated by at least one week. During each session, participants completed the Yo-Yo intermittent-recovery-test level-1 (YYIRT-1) at ~20:00 h. Then, sleep polysomnography was recorded from 22:15 min to 07:00 h, after a double blind randomized order administration of a single 10-mg tablet of MEL (MEL-10 mg) or Placebo (PLA). The following morning, Hooper wellness index was administered and the participants performed the Choice Reaction Time (CRT) test, the Zazzo test and some short-term physical exercises (YYIRT-1, vertical and horizontal Jumps (VJ; HJ), Hand grip strength (HG), and five-jump test (5-JT)). Evening total distance covered in the YYIRT-1 did not change during the two conditions (p > 0.05). Total sleep time (Δ = 24.55 mn; p < 0.001), sleep efficiency (Δ = 4.47%; p < 0.001), stage-3 sleep (N3 sleep) (Δ = 1.73%; p < 0.05) and rapid-eye-movement sleep (Δ = 2.15%; p < 0.001) were significantly higher with MEL in comparison with PLA. Moreover, sleep-onset-latency (Δ = -8.45mn; p < 0.001), total time of nocturnal awakenings after sleep-onset (NA) (Δ = -11 mn; p < 0.001), stage-1 sleep (N1 sleep) (Δ = -1.7%; p < 0.001) and stage-2 sleep (N2 sleep) (Δ = -1.9%; p < 0.05) durations were lower with MEL. The Hooper index showed a better subjective sleep quality, a decrease of the subjective perception of fatigue and a reduced level of muscle soreness with MEL. Moreover, MEL improved speed and performance but not inaccuracy during the Zazzo test. CRT was faster with MEL. Morning YYIRT-1 (Δ = 82 m; p < 0.001) and 5-JT (Δ = 0.08 m; p < 0.05) performances were significantly higher with MEL in comparison with PLA. In contrast, HG, VJ and HJ performances did not change during the two conditions (p > 0.05). The administration of a single dose of MEL-10 mg after strenuous late-evening exercise improved sleep quality and quantity, selective attention, subjective assessment of the general wellness state, and some short-term physical performances the following morning in healthy teenagers.

Drugs for insomnia

INTRODUCTION

Sleep is a vital neurochemical process involving sleep-promoting and arousal centers in the brain. Insomnia is a pervasive disorder characterized by difficulties in initiating or maintaining or non-refreshing (poor quality) sleep and clinically significant daytime distress. Insomnia is more prevalent in women and old age and puts sufferers at significant physical and mental health risks. This review summarizes published data on the current and emerging insomnia drug classes, rationale for development and associated risks/benefits. (Summary of Product Characteristics and Medline search on "hypnotic" or specific drug names and "Insomnia").

AREAS COVERED

GABA(A) receptor modulators facilitate sleep onset and some improve maintenance but increase risk of dependence, memory, cognitive and psychomotor impairments, falls, accidents and mortality. Melatonin receptor agonists improve quality of sleep and/or sleep onset but response may develop over several days. They have more benign safety profiles and are indicated for milder insomnia, longer usage and (prolonged release melatonin) older patients. Histamine H-1 receptor antagonists improve sleep maintenance but their effects on cognition, memory and falls remain to be demonstrated. Late-stage pipeline orexin OX1/OX2 and serotonin 5HT2A receptor antagonists may hold the potential to address several unmet needs in insomnia pharmacotherapy but safety issues cast some doubts over their future.

EXPERT OPINION

Current and new insomnia drugs in the pipeline target different sleep regulating mechanisms and symptoms and have different tolerability profiles. Drug selection would ideally be based on improvement in the quality of patients' sleep, overall quality of life and functional status weighed against risk to the individual and public health.

Melatonin agonists in primary insomnia and depression-associated insomnia: are they superior to sedative-hypnotics?

Current pharmacological treatment of insomnia involves the use of sedative-hypnotic benzodiazepine and non-benzodiazepine drugs. Although benzodiazepines improve sleep, their multiple adverse effects hamper their application. Adverse effects include impairment of memory and cognitive functions, next-day hangover and dependence. Non-benzodiazepines are effective for initiating sleep but are not as effective as benzodiazepines for improving sleep quality or efficiency. Furthermore, their prolonged use produces adverse effects similar to those observed with benzodiazepines. Inasmuch as insomnia may be associated with decreased nocturnal melatonin, administration of melatonin is a strategy that has been increasingly used for treating insomnia. Melatonin can be effective for improving sleep quality without the adverse effects associated with hypnotic-sedatives. Ramelteon, a synthetic analog of melatonin which has a longer half life and a stronger affinity for MT1 and MT2 melatonergic receptors, has been reportedly effective for initiating and improving sleep in both adult and elderly insomniacs without showing hangover, dependence, or cognitive impairment. Insomnia is also a major complaint among patients suffering from depressive disorders and is often aggravated by conventional antidepressants especially the specific serotonin reuptake inhibitors. The novel antidepressant agomelatine, a dual action agent with affinity for melatonin MT1 and MT2 receptors and 5-HT2c antagonistic properties, constitutes a new approach to the treatment of major depressive disorders. Agomelatine ameliorates the symptoms of depression and improves the quality and efficiency of sleep. Taken together, the evidence indicates that MT1/MT2 receptor agonists like ramelteon or agomelatine may be valuable pharmacological tools for insomnia and for depression-associated insomnia.

Morning Melatonin Has Limited Benefit as a Soporific For Daytime Sleep After Night Work

Exogenous melatonin administration in humans is known to exert both chronobiotic (phase shifting) and soporific effects. In a previous study in our lab, young, healthy, subjects worked five consecutive simulated night shifts (23:00 to 07:00 h) and slept during the day (08:30 to 15:30 h). Large phase delays of various magnitudes were produced by the study interventions, which included bright light exposure during the night shifts, as assessed by the dim light melatonin onset (DLMO) before (baseline) and after (final) the five night shifts. Subjects also ingested either 1.8 mg sustained-release melatonin or placebo before daytime sleep. Although melatonin at this time should delay the circadian clock, this previous study found that it did not increase the magnitude of phase delays. To determine whether melatonin had a soporific effect, we controlled the various magnitudes of phase delay produced by the other study interventions. Melatonin (n=18) and placebo (n=18) groups were formed by matching a melatonin participant with a placebo participant that had a similar baseline and final DLMO (+/-1 h). Sleep log measurements of total sleep time (TST) and actigraphic measurements of sleep latency, TST, and three movement indices for the two groups were examined. Although melatonin was associated with small improvements in sleep quality and quantity, the differences were not statistically significant by analysis of variance. However, binomial analysis indicated that melatonin participants were more likely to sleep better than their placebo counterparts on some days with some measures. It was concluded that, the soporific effect of melatonin is small when administered prior to 7 h daytime sleep periods following night shift work.

An evaluation of the neuroendocrine response to sleep in pediatric burn patients

INTRODUCTION

Previous work demonstrated reduced stage 3+4 and rapid eye movement (REM) sleep following burn injury. This study evaluated the hormonal effects of drug intervention on measures of endocrine status. A secondary objective examined the relationship between hormones and sleep stage distribution.

METHODS

Forty patients 3-18 years of age with a mean percent total body surface area burn of 50.1 +/- 2.9 were randomly assigned to zolpidem or haloperidol utilizing a blinded crossover design. Polysomnography was performed 6 nights, 3/week over 2 weeks. Each week's first night of monitoring was conducted without medication, serving as a baseline. Hormonal levels (epinephrine, norepinephrine, growth hormone, melatonin, dehydroepiandrosterone [DHEA], serotonin, cortisol) were obtained at 0600 h each study day.

RESULTS

Both drugs were associated with increased DHEA levels (P < .03); no other hormones were affected by medication. Significant inverse correlation was observed between REM sleep and epinephrine (r = -.34, P = .004) and norepinephrine levels (r = -.45, P = .02). A positive relationship existed between serotonin and sleep stage 3+4 (r = 0.24, P = .01) and REM (r = 0.48, P = .01). No other significant associations were identified between hormones and sleep.

CONCLUSIONS

This work characterizes the relationship between sleep deprivation and select endocrine parameters postburn. Drug interventions utilized in this study were either ineffective or insufficient in modulating improved hormonal response. Significance of zolpidem's and haloperidol's effect on serum levels of DHEA is unclear. The inverse correlation of epinephrine with REM may suggest that hypermetabolism associated with burns is partly due to lack of REM sleep. Questions remain regarding the effects of sleep deprivation on metabolism and clinical outcome.

Assessment of the Potential Role of Tryptophan as the Precursor of Serotonin and Melatonin for the Aged Sleep-wake Cycle and Immune Function: Streptopelia Risoria as a Model

In the present review we summarize the relationship between the amino acid, tryptophan, the neurotransmitter, serotonin, and the indole, melatonin, with the rhythms of sleep/wake and the immune response along with the possible connections between the alterations in these rhythms due to aging and the so-called “serotonin and melatonin deficiency state.” The decrease associated with aging of the brain and circulating levels of serotonin and melatonin seemingly contributes to the alterations of both the sleep/wake cycle and the immune response that typically accompany old age. The supplemental administration of tryptophan, e.g. the inclusion of tryptophan-enriched food in the diet, might help to remediate these age-related alterations due to its capacity of raise the serotonin and melatonin levels in the brain and blood. Herein, we also summarize a set of studies related to the potential role that tryptophan, and its derived product melatonin, may play in the restoration of the aged circadian rhythms of sleep/wake and immune response, taking the ringdove (Streptopeliarisoria) as a suitable model.

Role of the melatonin system in the control of sleep: therapeutic implications

The circadian rhythm of pineal melatonin secretion, which is controlled by the suprachiasmatic nucleus (SCN), is reflective of mechanisms that are involved in the control of the sleep/wake cycle. Melatonin can influence sleep-promoting and sleep/wake rhythm-regulating actions through the specific activation of MT(1) (melatonin 1a) and MT(2) (melatonin 1b) receptors, the two major melatonin receptor subtypes found in mammals. Both receptors are highly concentrated in the SCN. In diurnal animals, exogenous melatonin induces sleep over a wide range of doses. In healthy humans, melatonin also induces sleep, although its maximum hypnotic effectiveness, as shown by studies of the timing of dose administration, is influenced by the circadian phase. In both young and elderly individuals with primary insomnia, nocturnal plasma melatonin levels tend to be lower than those in healthy controls. There are data indicating that, in affected individuals, melatonin therapy may be beneficial for ameliorating insomnia symptoms. Melatonin has been successfully used to treat insomnia in children with attention-deficit hyperactivity disorder or autism, as well as in other neurodevelopmental disorders in which sleep disturbance is commonly reported. In circadian rhythm sleep disorders, such as delayed sleep-phase syndrome, melatonin can significantly advance the phase of the sleep/wake rhythm. Similarly, among shift workers or individuals experiencing jet lag, melatonin is beneficial for promoting adjustment to work schedules and improving sleep quality. The hypnotic and rhythm-regulating properties of melatonin and its agonists (ramelteon, agomelatine) make them an important addition to the armamentarium of drugs for treating primary and secondary insomnia and circadian rhythm sleep disorders.

Sleep, circadian rhythms, and delayed phase in adolescence

Sleep/wake timing shifts later in young humans during the second decade of life. In this review we describe sleep/wake patterns, changes in these patterns across adolescence, and evidence for the role of environmental, psychosocial, and biological factors underlying these changes. A two-process model incorporating circadian (Process C) and sleep/wake homeostatic (Process S) components is outlined. This model may help us to understand how developmental changes translate to shifted sleep/wake patterns. Delayed sleep phase syndrome (DSPS), which has a typical onset during the second decade of life, may be an extreme manifestation of homeostatic and circadian changes in adolescence. We describe symptoms, prevalence, and possible etiology of DSPS, as well as treatment approaches in adolescents.

Sleep and intercontinental flights

At present there are no 'high-tech' solutions to the problems that may beset intercontinental travellers. Indications for the use of drugs are limited, and their use must accord with Good Clinical Practice. Essentially, travellers must look after their sleep, as far as possible, during and after the flight. The most useful time for sleep during the flight must be anticipated, caution exercised in the use of hypnotics in-flight as reduced mobility is a potential risk factor for venous thrombosis, and a strategy adopted, whether flying east or west, to adapt as quickly as possible to the working hours of the new locality. After an eastward flight a hypnotic may be useful, but this strategy is seldom necessary after a westward flight unless the journey has involved crossing more than 5 or 6 time zones. The claim that melatonin accelerates the shift of the sleep-wakefulness cycle to a new time zone is controversial, and its recommended use may prejudice alertness during working hours. Exposure to artificial light and avoidance of ambient light at certain times of the day could prove to be of help-possibly in conjunction with drugs. However, effective and practical alterations in the light environment must be devised before such strategies can be considered with confidence.

The relationship between the rate of melatonin excretion and sleep consolidation for locomotive engineers in natural sleep settings

Background

The aim of the study was to examine the role that melatonin production plays in the regulation of sleep consolidation in a population of shiftworkers working and sleeping in their natural environments.

Methods

253 locomotive engineers (249 male, 4 female, mean age = 39.7 years) participated in the study for a 2-week period whilst working their normal roster patterns. Participants recorded details for all sleep periods in a sleep diary and collected urine samples during each day's main sleep period. The samples were subsequently assayed for the metabolite of melatonin in urine, 6-sulphatoxymelatonin (aMT6s), and the rate of excretion during main sleep periods was calculated.

Results

Separate one-way factorial ANOVAs revealed a significant effect of time of sleep onset on aMT6s excretion rate, sleep duration, and subjective sleep quality. Generally, the rate of aMT6s excretion was lower, sleep duration was shorter, and sleep quality was lower for sleeps initiated during the daytime than for sleeps initiated at night.

Conclusion

Combined with previous studies linking melatonin production and sleep propensity, and others demonstrating the relationship between sleep consolidation and melatonin production in forced desynchrony protocols, the current results indicate that low production of melatonin may play a role in the poor consolidation of daytime sleep in natural sleep settings.

Relationship between individual difference in melatonin suppression by light and habitual bedtime

The purpose of this study was to determine the relationship between individual difference in melatonin suppression by exposure to light and habitual bedtime. Seventeen healthy male students (mean age: 22.6+/-2.4 yr) volunteered to participate in the study. The subjects were exposed to light (1000 lx) for 2 hours from 2 hours before the time of peak salivary melatonin concentration. Two hours after exposure to the light, melatonin suppression had occurred in fifteen subjects. No significant correlation was found between the rate of melatonin suppression and habitual bedtime in the fifteen subjects in whom melatonin suppression occurred. However, the habitual bedtime of the two subjects in whom melatonin suppression did not occur was earlier than that of the other subjects. These results suggest that there are some people with very low sensitivity to light and that this may affect habitual bedtime.

Melatonin and sleep in aging population

The neurohormone melatonin is released from the pineal gland in close association with the light-dark cycle. There is a temporal relationship between the nocturnal rise in melatonin secretion and the 'opening of the sleep gate' at night. This association, as well as the sleep promoting effect of exogenous melatonin, implicates the pineal product in the physiological regulation of sleep. Aging is associated with a significant reduction in sleep continuity and quality. A decreased production of melatonin with age is documented in a majority of studies. Diminished nocturnal melatonin secretion with severe disturbances in sleep/wake rhythm has been consistently reported in Alzheimer's disease (AD). A recent survey on the effects of melatonin in sleep disturbances, including all age groups, failed to document significant and clinically meaningful effects of exogenous melatonin on sleep quality, efficiency and latency. However, in clinical trials involving elderly insomniacs and AD patients suffering from sleep disturbances exogenous melatonin has repeatedly been found to be effective in improving sleep. The results indicate that exogenous melatonin is more effective to promote sleep in the presence of a diminished production of endogenous melatonin. A MT1/MT2 receptor analog of melatonin (ramelteon) has recently been introduced as a new type of hypnotics with no evidence of abuse or dependence.

Melatonin as a hypnotic: pro

In diurnal species, nocturnal melatonin secretion coincides with the habitual hours of sleep, in contrast to nocturnal animals which are at the peak of their activity while producing melatonin. Studies in humans, diurnal non-human primates, birds and fish show that melatonin treatment can facilitate sleep initiation during the daytime or improve altered overnight sleep. Behaviorally, the sleep-promoting effects of melatonin are distinctly different from those of common hypnotics and are not associated with alterations in sleep architecture. The effects of melatonin on sleep are mediated via specific melatonin receptors and physiologic doses of the hormone, those inducing circulating levels under 200 pg/ml, are sufficient to promote sleep in diurnal species. Aging reduces responsiveness to melatonin treatment and this correlates with reduced functional potency of melatonin receptors. Since melatonin receptors are present in different tissues and organs and involved in multiple physiologic functions, using physiologically relevant doses (0.1-0.3 mg, orally) and time of administration (at bedtime) is recommended, in order to avoid known and unknown side effects of melatonin treatment.

Hipnoindutores e insônia

O objetivo deste artigo de atualização é o de descrever brevemente o perfil, a utilização clínica e a indicação de alguns dos sedativos e compostos hipnóticos mais utilizados. Cerca de 2/3 de todas as prescrições hipnóticas vão para o uso crônico. Os benzodiazepínicos estão entre as drogas mais prescritas mundialmente. As mulheres, os idosos e os pacientes psiquiátricos e clínicos estão entre os usuários crônicos de hipnóticos. O zolpidem é, atualmente, o hipnótico mais prescrito na maioria dos países. Parece ser mais seguro em comparação aos benzodiazepínicos e poderia ser uma opção para o uso de longo prazo e controlado ("quando necessário"). Os antidepressivos sedativos encontram-se também entre as medicações mais prescritas para sedação em pacientes com insônia nos EUA e no Reino Unido. São descritos efeito sedativo e uso de trazodona, mirtazapina, doxepina e amitriptilina. Os autores também discutem o uso de melatonina e suas propriedades sedativas e o uso racional de antipsicóticos sedativos para insônia crônica, em especial em pacientes psiquiátricos. Finalmente, alguns compostos fitoterápicos são mencionados.

Advances in the management of insomnia

Insomnia is a prevalent disorder, altering night time sleep, daytime mood and performance. Current treatment strategies, used separately or in combination, include pharmacological, circadian, behavioural and cognitive therapy. An increased diversity of available hypnotics with different potency, pharmacodynamic and pharmacokinetic profiles and improved side effect profiles provides more flexibility in designing individual treatment strategies. Melatonin, a pineal hormone with acute sleep-promoting and chronobiotic properties, allows additional possibilities in treating insomnia and circadian sleep disorders. Current studies of processes involved in normal sleep regulation and pathophysiology of insomnia should result in the development of new medications based on physiological mechanisms of sleep.

Sleep-inducing effects of exogenous melatonin administration

In this report current data is reviewed indicating that melatonin, the main hormone secreted by the pineal gland at night, participates in sleep regulation in humans. Evidence supporting this role relies on findings that abnormal melatonin secretion, induced by a variety of commonly used drugs, and in clinical disorders of the nervous system, are associated with sleep disturbances, and that melatonin has beneficial sleep-inducing effects in elderly melatonin-deficient insomniacs, and in children with sleep disorders. The time of melatonin administration, rather than the pharmacological dose, is a crucial factor regarding its potency as a sleep-inducing agent. Possible operating mechanisms explaining melatonin hypnotic effects are discussed.

Residual effects of daytime administration of melatonin on performance relevant to flight

There is a general consensus that melatonin possesses time-dependent hypnotic effects, but there is no information yet whether it has residual effects on neurobehavioral performance, especially after daytime administration. In the present study we investigated the possible residual effects of 3 mg melatonin on performance relevant to flight and on subjective feelings of sleepiness, arousal, activation and affect after a daytime nap, as a function of nap length. Fifteen reserve pilots of the Israeli Air Force participated in the study. The experiment consisted of four sessions during which either melatonin or placebo was administered at 16:00 h. In two conditions, subjects were allowed to sleep for 2 h (17:00-19:00 h) whereas in the other two only a 0.5-h nap was allowed. After the naps they started performing a flight simulator task every 2 h. Sleep efficiency significantly increased and sleep latency significantly decreased in both melatonin conditions compared to placebo. Flight performance was only mildly affected in the 0.5-h nap condition. Subjective assessment of sleepiness significantly differed between the two treatment conditions, only in the 0.5-h nap condition. Subjects felt sleepier 2-4 h after melatonin administration. To conclude, our data suggest that administration of melatonin before a brief daytime nap (about 0.5 h) may be associated with mild residual effects on psychomotor performance and may significantly affect subjective feeling of sleepiness for 2-4 h.

Melatonin and sleep qualities in healthy adults: pharmacological and expectancy effects

The impact of expectancy on melatonin's effects on sleep qualities was investigated. Both the pharmacological dose of 6 mg of melatonin and the expectation of receiving melatonin were predicted to improve subjective ratings of sleep qualities. The balanced placebo design varied 2 factors within-subjects: actual treatment and expected treatment. Adults (N = 53; 21 men and 32 women) between the ages of 26 and 71 years were administered either 6 mg of melatonin or a placebo for 8 nights. An instructional manipulation directed participants' expectations. Participants rated their nightly sleep experiences. Results revealed that feelings upon awakening differed between genders and that expecting melatonin increased ratings of sleep continuity. Most important, high ratings of "grogginess/tiredness" were associated with receiving melatonin, regardless of expectancy, as well as with receiving placebo when melatonin was expected. Overall, the findings underscore the need to consider expectancy and gender differences in research on melatonin and sleep experiences.

Effects of melatonin administration on daytime sleep after simulated night shift work

Disturbed sleep and on-the-job sleepiness are widespread problems among night shift workers. The pineal hormone melatonin may prove to be a useful treatment because it has both sleep-promoting and circadian phase-shifting effects. This study was designed to isolate melatonin's sleep-promoting effects, and to determine whether melatonin could improve daytime sleep and thus improve night time alertness and performance during the night shift. The study utilized a placebo-controlled, double-blind, cross-over design. Subjects (n=21, mean age=27.0 +/- 5.0 years) participated in two 6-day laboratory sessions. Each session included one adaptation night, two baseline nights, two consecutive 8-h night shifts followed by 8-h daytime sleep episodes and one recovery night. Subjects took 1.8 mg sustained-release melatonin 0.5 h before the two daytime sleep episodes during one session, and placebo before the daytime sleep episodes during the other session. Sleep was recorded using polysomnography. Sleepiness, performance, and mood during the night shifts were evaluated using the multiple sleep latency test (MSLT) and a computerized neurobehavioral testing battery. Melatonin prevented the decrease in sleep time during daytime sleep relative to baseline, but only on the first day of melatonin administration. Melatonin increased sleep time more in subjects who demonstrated difficulty in sleeping during the day. Melatonin had no effect on alertness on the MSLT, or performance and mood during the night shift. There were no hangover effects from melatonin administration. These findings suggest that although melatonin can help night workers obtain more sleep during the day, they are still likely to face difficulties working at night because of circadian rhythm misalignment. The possibility of tolerance to the sleep-promoting effects of melatonin across more than 1 day needs further investigation.

Human aging and melatonin. Clinical relevance

Melatonin is a hormone produced mainly by the pineal gland and secreted primarily at night, when it reaches levels 10 times higher than those present in the daytime. The highest melatonin levels are found in children younger than 4 yr; thereafter melatonin levels begin to decline with age. As a chronobiotic, melatonin acts on sleep by phase-advancing or delaying the sleep--wake cycle so that sleep onset occurs earlier or later than usual. Beneficial effects of melatonin have been observed in delayed and advanced sleep phase syndromes. These effects depend on the time that the hormone is administered. Melatonin is also used for jet lag and has been tried in shift workers and night workers to re-entrain their desynchronized rhythms. Melatonin also has free radical-scavenging properties that have primarily been observed in vitro at pharmacological concentrations.

Hypnotic action of melatonin during daytime administration and its comparison with triazolam

The present study was conducted to assess hypnotic action, effects on rectal temperature and dose dependency by daytime administration of exogenous melatonin (MLT) at 1 mg, 3 mg or 6 mg to subjects consisting of seven healthy juvenile adults. As a result, exogenous MLT significantly increased total sleep time and sleep efficiency, and MLT 6 mg was observed to demonstrate hypnotic effects that were nearly equal to those of triazolam at 0.125 mg. Rectal temperature was significantly decreased at MLT 1mg and 3 mg, there were no significant differences observed in the hypothermic effects at MLT 6 mg. These results indicate that exogenous MLT had dose-dependent hypnotic action on daytime sleep, and it is possible to consider that this hypnotic action was based on a direct-acting mechanism.

Melatonin for chronic sleep onset insomnia in children: a randomized placebo-controlled trial

To establish the efficacy of melatonin treatment in childhood sleep onset insomnia, 40 elementary school children, 6 to 12 years of age, who suffered more than 1 year from chronic sleep onset insomnia, were studied in a double-blind, placebo-controlled study. The children were randomly assigned to receive either 5-mg melatonin or placebo. The study consisted of a 1-week baseline, consecutively followed by a 4-week treatment period. After that period, treatment was continued if the parents wished so. The study's impact was assessed by measurements of lights-off time, sleep onset, and wake-up time, recorded in a diary (n = 33). Sleep onset was also recorded with an actigraph (n = 25). Endogenous dim light melatonin onset was measured in saliva (n = 27). Sustained attention was evaluated with the Bourdon-Vos reaction time test (n = 36). In the melatonin group, mean (95% CI) lights-off time advanced 34 (6-63) minutes, diary sleep onset 63 (32-94) minutes, actigraphic sleep onset 75 (36-114) minutes, and melatonin onset 57 (24 to 89) minutes; total sleep time increased 41 (19-62) minutes. In the placebo group, these parameters did not shift significantly. The change during the 4-week treatment period differed between the treatment groups significantly as to lights-off time, diary and actigraphic sleep onset, sleep duration, and melatonin onset. There were no significant differences between the treatment groups in the change of sleep latency, wake-up time, and sustained attention reaction times. Mild headache occurred in 2 children during the first 2 days of the melatonin treatment. Eighteen months after the start of the trial, in 13 of the 38 children who could be followed up, melatonin treatment was stopped because their sleep problem was solved and in 1 child because sleep was not improved. Twelve children used melatonin 5 mg, the other 1.0 to 2.5 mg. One child developed mild generalized epilepsy 4 months after the start of the trial. The results show that melatonin, 5 mg at 6 PM, was relatively safe to take in the short term and significantly more effective than placebo in advancing sleep onset and dim light melatonin onset and increasing sleep duration in elementary school children with chronic sleep onset insomnia. Sustained attention was not affected.

Age-related changes in melatonin levels in humans and its potential consequences for sleep disorders

Prior to three months of age there is little melatonin (MLT) secretion in humans. MLT production then commences, becomes circadian, and reaches its highest nocturnal blood levels between the ages of one to three years. During the remainder of childhood, nocturnal peak levels drop progressively by 80%. In adults, these levels show an additional drop of some 10%, mainly during senescence. The large drop in serum MLT during childhood is probably the result of the increase in size of the human body, despite a constant MLT production after infancy. The additional decline of MLT with higher age may be due to a yet unidentified physiological mechanism accompanying senescence. The biological significance of these MLT alterations remains unknown. Since the discovery of MLT, an immediate sedative action of this hormone has been known. A number of recent studies have demonstrated that MLT indeed exerts a sleep-promoting action by accelerating sleep initiation, improving sleep maintenance, and marginally altering sleep architecture. The potential of MLT in the treatment of insomnia is being explored, and the results are promising. Although in most of these studies pharmacological dosages of MLT have been used, preliminary data suggest that similar effects can also be achieved by physiological hormone concentrations. The latter observation raises the question of whether MLT might be involved in the physiological control of sleep.

Does exogenous melatonin improve day sleep or night alertness in emergency physicians working night shifts?

STUDY OBJECTIVE

To determine whether exogenous melatonin improves day sleep or night alertness in emergency physicians working night shifts.

METHODS

In a double-blind, placebo-controlled crossover trial, emergency physicians were given 10 mg sublingual melatonin or placebo each morning during one string of nights and the other substance during another string of nights of equal duration. During day-sleep periods, subjective sleep data were recorded. During night shifts, alertness was assessed with the use of the Stanford Sleepiness Scale. Key outcome comparisons were visual analog scale scores for gestalt night alertness and for gestalt day sleep for the entire string of nights.

RESULTS

We analyzed data from 18 subjects. Melatonin improved gestalt day sleep (P = .3) and gestalt night alertness (P = .03) but in neither case was the improvement statistically significant. Of 13 secondary comparisons, 9 showed a benefit of melatonin over placebo; none showed a benefit of placebo over melatonin.

CONCLUSION

Exogenous melatonin may be of modest benefit to emergency physicians working night shifts.

Beyond benzodiazepines: alternative pharmacologic agents for the treatment of insomnia

OBJECTIVE

To review the epidemiology, etiology, and classification of insomnia and provide an overview of the pharmacologic therapy of insomnia. Novel nonbenzodiazepine hypnotics including zolpidem, zopiclone, and zaleplon, as well as nonprescription products such as valerian and melatonin, are reviewed in detail.

DATA SOURCES

A MEDLINE search was performed to identify relevant clinical studies, case reports, abstracts, and review articles published between April 1992 and December 1997. Key search terms included insomnia, benzodiazepines, zolpidem, zopiclone, zaleplon, Cl 284,846, melatonin, and valerian. Additional references were obtained from the lists of review articles and textbooks.

DATA EXTRACTION AND SYNTHESIS

Data concerning the safety and efficacy of the hypnotic agents were extracted from all available clinical trials and abstracts. Background information regarding insomnia, benzodiazepines, and other hypnotics was extracted from the most current literature, including review articles and textbooks.

CONCLUSIONS

New developments in benzodiazepine receptor pharmacology have introduced novel nonbenzodiazepine hypnotics that provide comparable efficacy to benzodiazepines. Although they may possess theoretical advantages over benzodiazepines based on their unique pharmacologic profiles, they offer few, if any, significant advantages in terms of adverse effects. Over-the-counter agents such as valerian and melatonin may be useful in alleviating mild, short-term insomnia, but further clinical trials are required to fully evaluate their safety and efficacy.

Melatonin--the key to the gate of sleep

This article reviews the evidence that melatonin, a hormone produced by the pineal gland during the dark hours, plays a major role in the regulation of the sleep-wake cycle. In recent years, our laboratory has been involved in a large-scale project aimed at investigating the role of endogenous melatonin in sleep-wake regulation and the effects of nonpharmacological levels of melatonin on sleep. Based on our finding on the precise coupling between the endogenous nocturnal increase in melatonin secretion and the opening of the nocturnal sleep gate, we propose that the role of melatonin in the induction of sleep does not involve the active induction of sleep, but is rather mediated by an inhibition of a wakefulness-producing mechanism in the central nervous system. Our studies also suggest that exogenously administered melatonin may be beneficial in certain types of insomnia that are related to disturbances in the normal secretion of the hormone.

Guidelines for prescribing melatonin

Although compelling logic suggests that melatonin may be effective for a variety of disorders, there are few empirical clinical studies. The optimal dose of melatonin is not clear; most studies have used doses that produce supraphysiological blood levels. The timing of melatonin administration is important. Melatonin has few immediate side-effects except drowsiness, but the effects of chronic administration are unclear. Melatonin may be effective in reducing jet lag. In elderly patients with poor sleep and documented low melatonin production, melatonin may be helpful. In several studies, melatonin has been shown to shorten sleep latency. Further studies are needed to clarify the efficacy and safety of melatonin.

Efficacy of melatonin as a hypnotic agent

The seemingly contradictory literature on the use of melatonin in insomnia is best understood by considering issues of time of administration (day or night), dose range (physiological or pharmacological), subject selection (normals or insomniacs), choice of dependent variable (self-report or electroencephalogram), and comprehensiveness of the reported variables (sleep onset or sleep maintenance). Available data on nighttime administration to normals and insomniacs are reviewed. It is concluded that there is not yet a convincing body of evidence, using generally accepted measures, that melatonin administration improves sleep in insomniacs with noncircadian sleep disturbance.

Responsiveness to melatonin and its receptor expression in the aging circadian clock of mice

This study determined the effect of age on the efficacy of melatonin treatment to phase shift circadian activity rhythms and on melatonin receptor expression in the suprachiasmatic nucleus (SCN) and paraventricular nucleus of the thalamus (PVNT) of C3H/HeN mice. The circadian rhythm of 2-[125I]iodomelatonin binding, assessed at three times of the day [circadian times (CT) 2, 10, and 18], showed a modest age-related decrease in the SCN but not the PVNT of old C3H/HeN mice (24 mo). There was a tendency for age to reduce Mel1a melatonin receptor mRNA expression in the suprachiasmatic nucleus during the day, but not during the night. The magnitude of phase shifts of circadian activity rhythms (advances or delays) induced by administration of melatonin at CT 10 or CT 2 was identical in young and old C3H/HeN mice. Together, these results suggest that the decrease in melatonin receptor expression in the SCN had little effect on melatonin-induced phase shifts of circadian activity rhythms. We conclude that the responsiveness of the circadian timing system to melatonin administration does not decrease with age.

Efficacy of melatonin as a sleep-promoting agent

Numerous studies have demonstrated sleep-promoting effects of melatonin treatment in humans, as evidenced by subjects' self-reports, polysomnographic recordings, and continuous actigraphic registration of motor activity. The sleep-promoting effects of either physiological or pharmacological doses of melatonin typically are observed within 1 h following treatment regardless of the time of melatonin administration. This fact indicates the acute nature of this effect of melatonin on sleep, independent of any effect of the melatonin treatment on circadian organization. This article considers a dose dependency of melatonin effects on sleep, interindividual variability, and age-related differences in circulating melatonin levels produced in response to a given dose of the hormone. Possible side effects of melatonin treatment, and the use of an animal model to serve as a guide in the development of therapeutic applications, also are considered.

Melatonin: role in gating nocturnal rise in sleep propensity

The present article reviews the evidence that melatonin possesses sleep-inducing effects and that it gates the increase in nocturnal sleepiness. It is shown that, without exception, all the studies that have investigated daytime administrations of melatonin reported increased sleepiness, even at doses that do not increase plasma levels of melatonin beyond its physiological levels. By contrast, nighttime increase in sleepiness was achieved only after administration of high doses. Based on these findings and on the precise coupling between the endogenous nocturnal increase in melatonin secretion and the opening of the sleep gate, it is suggested that melatonin participates in the regulation of the sleep-wake cycle by inhibiting the central nervous system wakefulness generating system. This inhibition allows a smooth transition from wakefulness to sleep. Clinical findings on decreased levels of nocturnal melatonin in chronic insomniacs, and on the efficacy of exogenous melatonin in improving sleep in melatonin-deficient insomniacs, are congruent with this hypothesis.

Effect of atenolol on nocturnal sleep and temperature in young men: reversal by pharmacological doses of melatonin

To examine the physiological role of melatonin in sleep, nocturnal melatonin secretion was suppressed using 100 mg oral atenolol in two studies. In Study 1, nocturnal sleep was recorded in 8 young men over 4 nights. Subjects received atenolol on one of the last 2 nights and showed significantly increased total wake time (TWT) and wakefulness after sleep onset (WASO), as well as decreased REM sleep and slow-wave sleep (SWS). When melatonin (total 5 mg) was given after atenolol on the other night, the changes in TWT, WASO, REM, and SWS were reversed. In Study 2, sleep onset latencies (SOL) and core temperature (Tc) of 10 young men were measured for 3 nonconsecutive nights. In a cross-over design, atenolol given on one night significantly suppressed urinary 6-sulphatoxymelatonin (6s-aMT) production and increased hourly measures of Tc and SOL relative to baseline night values. Oral melatonin (3 mg), administered after atenolol, reversed the changes in Tc and SOL. These results suggest that endogenous melatonin may assist in the maintenance of normal sleep architecture (Study 1) and also increase nocturnal sleep propensity by hypothermic effects (Study 2).

Melatonin — a chronobiotic and soporific hormone

In this report we review evidence that melatonin, a hormone produced by the pineal gland during the hours of darkness, plays a major role in the synchronization of the sleep/wake cycle. The production of melatonin is regulated by a structure located in the hypothalamus called the suprachiasmatic nucleus (SCN). The activity of the SCN is strongly affected by changes in illumination and, as a consequence, melatonin levels are high during darkness and low in the light and it, therefore, reflects the cycle. Changes in sleep/wake patterns are among the hallmarks of biological aging. Complaints of difficulty in initiating and maintaining sleep, and daytime drowsiness, are more common in the elderly than in any other age group. In this report, we review evidence that impaired meltonin secretion is associated with sleep disorders in old age. Circulating melatonin levels have been found to be significantly lower in elderly insomniacs than in age-matched controls, and their onset and peak times delayed. In view of these findings, we investigated the effects of melatonin treatment on melatonin-deficient insomnia in the elderly. From the results of our study, it seems likely that melatonin replacement therapy may be beneficial in the initiation and maintenance of sleep in this population.

Relationship between napping and melatonin in the blind

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.

Hypnotic and hypothermic effects of melatonin on daytime sleep in humans: lack of antagonism by flumazenil

In this double-blind, placebo-controlled study we investigated whether 10 mg flumazenil, a pure benzodiazepine antagonist, can block the hypnotic and hypothermic effects of 3 mg melatonin. The design comprised four 7-h (1200-1900 h) testing periods, preceded by a 'no-treatment' adaptation period of the "7/13' sleep-wake paradigm. Six young healthy adult males were paid to participate. During each experimental period, tablets were administered at 1145 h (flumazenil or placebo) and at 1200 h (melatonin or placebo) in a randomized, double-blind, partially repeated Latin square design. Polysomnographic recordings and core body temperature recordings revealed that melatonin, either in combination with placebo or with flumazenil, significantly increased the amounts of sleep, and decreased core body temperature in comparison with placebo alone or the combination of flumazenil plus placebo. These results do not support the hypothesis that melatonin exerts its hypothermic and hypnotic effects via the central benzodiazepine receptors.

Nocturnal secretory patterns of melatonin, luteinizing hormone, prolactin and cortisol in male patients with gonadotropin-releasing hormone deficiency

To clarify whether disorders of gonadotropin releasing hormone (GnRH) deficiency are associated with altered melatonin and pituitary hormones secretory patterns, we studied male patients with hypogonadotropic hypogonadism (IGD; n = 6), delayed puberty (DP; n = 7) and age-matched pubertal controls (n = 7). Serum samples for the determination of melatonin, luteinizing hormone (LH), prolactin and cortisol levels were obtained at 15 min intervals from 1900 to 0700 in a controlled light-dark environment, complete bed-rest and fasting with simultaneous sleep recordings. Mean (+/- SD) dark-time melatonin levels were significantly higher in IGD (286 +/- 26 pmol/L) and DP (205 +/- 44 pmol/L) compared with 178 +/- 64 pmol/L in controls (P < 0.003). So were the mean (+/- SD) peak melatonin levels (453 +/- 63, 346 +/- 106 and 292 +/- 96 pmol/L) in IGD, DP and controls, respectively (P < 0.03). Integrated nocturnal melatonin (AUC) values were also higher in IGD and DP (184 +/- 15 and 134 +/- 28 pmol/min/L x 10(3)) compared with 116 +/- 42 pmol/min/L x 10(3) in controls (P < 0.003). The time of onset of the nocturnal melatonin rise was observed earlier in IGD and DP patients as compared to controls. No correlations were found between melatonin and LH levels, between melatonin and prolactin levels, or between melatonin and cortisol levels. These data indicate that melatonin secretion is enhanced in male patients with GnRH deficiency. The lack of correlation between melatonin and LH suggest that circulating gonadal steroids, rather than LH, modulate melatonin secretion in a reverse fashion.

Melatonin effect on daytime sleep in men: suppression of EEG low frequency activity and enhancement of spindle frequency activity

The effect of melatonin (5 mg, p.o.) on electroencephalographic (EEG) activity during sleep was investigated in eight men in a placebo-controlled cross-over design. Melatonin was administered immediately prior to a 4-h daytime sleep episode (13-17 h) after a partial sleep deprivation. The non-REM sleep stages and REM sleep duration were not significantly affected. Melatonin enhanced EEG power density in non-REM sleep in the 13.75-14.0 Hz bin (i.e., within the frequency range of sleep spindles), and reduced activity in the 15.25-16.5 Hz band. In the first 2 h spectral values within the 2.25-5.0 Hz range were reduced. These changes in the EEG are to some extent similar to those induced by benzodiazepine hypnotics and to the contribution of the endogenous circadian pacemaker to the spectral composition of the sleep EEG when sleep occurs at night.