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Melatonin for sleep: how it works, adverse effects
Last reviewed: 06.07.2025

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Melatonin is a hormone produced by the pineal gland that regulates circadian rhythms. It is obtained from animals or manufactured artificially.
How does melatonin work?
Some scientific evidence suggests that melatonin may be useful in minimizing the effects of long-haul flights, especially in people traveling east and crossing more than 2-5 time zones (see the Cochrane Central Register of Controlled Trials abstract on the role of melatonin in preventing and treating jet lag).
Standard dosage has not been established, but ranges from 0.5–5 mg orally taken 1 hour before usual bedtime on the day of travel and 2–4 mg at night after arrival. There is less evidence to support the use of melatonin as a sleep promoter in adults and children with neuropsychiatric disorders (e.g., developmental disabilities).
Antioxidant effects of melatonin
The physiological effects of melatonin have been studied in animals for over 20 years. Only in recent years have studies begun to study the mechanisms of synthesis, regulation and functions of this hormone in the human body. Melatonin is an indole by its chemical structure, mainly produced by the pineal gland from tryptophan. The rhythm of melatonin production by the pineal gland is circadian. Its level in circulation begins to increase in the evening, reaching a maximum by the middle of the night, and then progressively decreases, reaching a minimum in the morning.
In contrast to the biorhythmological effects of melatonin, which are mediated by its receptors on cell membranes, the antioxidant properties of this hormone are not mediated through its receptors. In vitro studies using a method for determining the presence of one of the most active free radicals OH in the test medium have shown that melatonin has a significantly more pronounced activity in terms of OH inactivation than such powerful intracellular antioxidants as glutathione and mannitol. It has also been demonstrated in vitro that melatonin has a stronger antioxidant activity with respect to the peroxyl radical ROO than the well-known antioxidant vitamin E. The protective effect of exogenous melatonin with respect to free-radical damage caused by exposure to ionizing radiation has been demonstrated on human leukocytes in vitro.
An interesting fact, indirectly indicating the priority role of melatonin as a DNA protector, was revealed during the study of cell proliferation activity. The revealed phenomenon indicates the leading role of endogenous melatonin in the mechanisms of antioxidant protection.
The role of melatonin in protecting macromolecules from oxidative stress is not limited to nuclear DNA. When studying the effect of free radical damage on tissues in an experiment, it was found that it is highly effective in preventing the occurrence of lens degeneration (clouding). Moreover, the protein-protective effects of this hormone are comparable to those of glutathione (one of the most powerful endogenous antioxidants. Therefore, melatonin also has protective properties in relation to free radical damage to proteins.
Of course, of great interest are the studies that show the role of this hormone in interrupting lipid peroxidation (LPO) processes. Until recently, vitamin E (a-tocopherol) was considered one of the most powerful lipid antioxidants. In vitro and in vivo experiments comparing the effectiveness of vitamin E and melatonin showed that melatonin is 2 times more active in terms of ROO inactivation than vitamin E. The authors also noted that such a high antioxidant effectiveness of this hormone cannot be explained only by the ability of melatonin to interrupt the lipid peroxidation process by inactivating ROO', but also includes the inactivation of the OH radical, which is one of the initiators of the LPO process.
In addition to the high antioxidant activity of the hormone itself, in vitro experiments have shown that its metabolite 6-hydroxymelatonin, formed during its metabolism in the liver, has a significantly more pronounced antioxidant effect on LPO than M. Consequently, in the body, mechanisms of protection against free-radical damage include not only the effects of the hormone, but also at least one of its metabolites.
One of the factors leading to the toxic effects of bacteria on the human body is the stimulation of LPO processes by bacterial lipopolysaccharides. An animal experiment demonstrated the high efficiency of the hormone in protecting against oxidative stress caused by bacterial lipopolysaccharides. The authors of the study emphasize that the antioxidant effect of the hormone is not limited to any one type of cell or tissue, but is of an organismic nature.
In addition to the fact that melatonin itself has antioxidant properties, it is able to stimulate glutathione peroxidase, which is involved in the conversion of reduced glutathione into its oxidized form. During this reaction, the H2O2 molecule, which is active in terms of producing the extremely toxic OH radical, is converted into a water molecule, and the oxygen ion is attached to glutathione, forming oxidized glutathione. It has also been shown that melatonin can inhibit the enzyme (nitric oxide synthase), which activates the processes of NO radical production.
The above-listed effects of the hormone allow us to consider it one of the most powerful endogenous antioxidants. Moreover, unlike most other intracellular antioxidants, localized mainly in certain cellular structures, its presence and, therefore, its antioxidant activity are determined in all cellular structures, including the nucleus. This fact indicates the universality of the antioxidant action of melatonin, which is confirmed by the above-mentioned experimental results demonstrating its protective properties in terms of free-radical damage to DNA, proteins and lipids. Due to the fact that the antioxidant effects of the hormone are not mediated through its membrane receptors, melatonin can affect free-radical processes in any cell of the human body, and not only in cells that have receptors for it.
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