There is substantial evidence that the prevalence of sleep disorders is an important occupational health problem, especially among health care professionals on night or on rotating work shifts 12345678910. An important aspect of the work environment of nurses is that they are required to work at any point in the 24 hour day 11. Night work is associated with disturbed sleep and impaired alertness. The impact of sleep is the result of the circadian interference with sleep during daylight hours and circadian suppression of pineal gland by light at night 12.

The definition of insomnia is a complaint of disturbed sleep, manifested as difficulties in sleep initiation, sleep maintenance, early morning awakenings, or nonrestorative sleep. Many sources also add the presence of associated daytime impairments, such as fatigue, irritability, decreased memory and concentration, and pervasive malaise affecting many aspects of daytime functioning 13. In a recent study, 32% of night-shift workers reported symptoms of insomnia or excessive daytime sleepiness, whereas these symptoms were reported in only 18% of day workers from the same sample population 14. Several studies have reported that sleep problems are more common among health care personnel on rotating work shifts 15. The quality of sleep has been found to be altered in hospital nurses working on rotating shift schedules, especially those working morning and night shifts as well as in hospital nurses working shifts when compared with day nurses 16.

The pineal hormone melatonin regulates a variety of physiological processes, including circadian, cardiovascular, reproductive, and neuroendocrine functions 171819. However, it is the hypnotic effects of melatonin that are considered an integral component of its physiological role in sleep modulation 2021. Administration of melatonin facilitates sleep onset and improves the quality of sleep 222324. Administration of melatonin can also produce phase shifts in circadian rhythms, and has been used to treat the symptoms of circadian maladaptation associated with shift work 252627. There is currently a great deal of interest in whether properly timed melatonin administration can facilitate circadian phase shifting in these situations 28.

Normally, production of melatonin by the pineal gland is stimulated by darkness and inhibited by light 29. Hajak et al 30 reported lower levels in blood melatonin in patients with insomnia than in healthy controls, and Haimov et al 31 found lower levels of urinary 6-sulphatoxymelatonin in elderly patients with insomnia than in healthy elderly subjects. Surprisingly, only a few studies have explored the beneficial effect of melatonin administration on night shift workers in an actual workplace setting 26. The purpose of this study was to compare the efficacy of melatonin (5 mg) and placebo in the treatment of shift workers with insomnia.

Eigthy-six out of 118 participants completed the study. Eleven subjects dropped out during the first treatment phase because they could not attend the scheduled tablet taking, whereas one did not complete the second treatment phase because of an acute illness unrelated to the study protocol. Twenty participants did not report sleeping problems in the baseline questionnaire. Table 1 presents a description of the 86 subjects who completed the study. Females accounted for 80.2% of the participants, and the mean age was 30.05 years (range: 24–46 years). Subjective parameters of sleep obtained from the baseline questionnaire are shown in Table 1.

Differences in sleep data at baseline, while taking placebo, and while taking melatonin are shown in Tables 2 and 3. Subjective sleep onset latency (SOL) was 37.5 +/- 41.3 minutes at the baseline. There was evidence of an effect of melatonin treatment on SOL. Specifically, the mean SOL for subjects being treated with melatonin was significantly lower than the mean SOL for subjects given placebo. Furthermore, means for both the subjects given melatonin and those given placebo were significantly different from the baseline mean (see Table 2). Although melatonin treatment did not significantly alter other insomnia variable compared with baseline values, there was a significant improvement in sleep quality with melatonin treatment (see Table 3).

In 86 shift-work nurses with insomnia disorders, administration of 5 mg of melatonin about 30 minutes before a night time sleep significantly decreased sleep onset latency (SOL) and increased sleep quality as compared with placebo. We observed a significant improvement in falling asleep induced by 5 mg of melatonin (16 min) as compared to baseline, which supports the well known capacity of this hormone to change biological rhythms 33343536.

Placebo was not equal to baseline for SOL. A general meta-analysis of placebo effects pointed to a nonsignificant beneficial effect on sleep latency (a 10-min decrease in subjective estimates of sleep latency) in five clinical trials 37. Melatonin did not alter the other sleep parameters that we measured. These findings are in accordance with those of earlier open trials using smaller numbers of subjects 3839.

The focus of our analysis was a comparison of assessment of insomnia parameters (sleep onset, sleep maintenance, sleep quality) in nurses with shift working at baseline, after a one-night melatonin treatment, and after a one-night placebo treatment. Our study revealed no major impact of melatonin on difficulty staying asleep or waking up too early. Our results agree with a previous investigation suggesting that patients with primary insomnia have a pathophysiologic disturbance that is not reversed by melatonin 40. No adverse effects of melatonin were noted during the treatment.

The fact that we observed a reduction in SOL but no change in sleep duration after melatonin administration has at least two possible explanations: either 1) melatonin caused a small (16 min) phase advance of the circadian system or 2) random variation obscured a correspondingly small lengthening of total sleep time. Our data do not provide the basis for favoring either one or the other of these alternatives.

A limitation of this study is that we were unable to perform polysomnography or actigraphy to evaluate sleep parameters objectively. Our results based on subjective self-reports were, however, very encouraging. Regarding the high prevalence of insomnia in shift workers, more studies about melatonin effect on different kinds of insomnia parameters (difficulty falling asleep, difficulty staying asleep, problem waking up too early, and sleep quality) causing by shift working is recommended.

Melatonin may be an effective treatment for shift workers with difficulty falling asleep.

The authors declare that they have no competing interests.

KHS helped with the conception and design of the study, helped to supervise the staff and helped to draft the manuscript. OA and GHP helped with the conception and design of the study and helped draft the manuscript. ZY helped with the conception and design of the study, helped to collect the data, participated in the data analyses and interpretation, and helped draft the manuscript. All authors read and approved the final manuscript.