Melatonin-the hormone that controls sleep and seasonal rhythms
It is a fact known to all that human beings, like all other animals, need to sleep . Sleep is a basic physiological function, a mechanism that allows the body (and especially the brain) to rest and repair itself. However, sleep is not a unique and invariable process, but rather it goes through different phases throughout the process. Moreover, it is a process that is not voluntary, but depends on circadian rhythms.
These rhythms regulate the sleep-wake cycle according to the body’s biological needs and the time of day. This regulation, as well as the seasonal patterns that occur in other animals, is mainly due to the action of a hormone: melatonin
Melatonin: What are we talking about?
Melatonin is a hormone secreted mainly by the pineal gland from tryptophan and serotonin. It is a very liposoluble hormone, with great facility to penetrate the blood-brain barrier and the interior of the cells. This hormone is generated when the retina perceives an absence of light, producing the maximum peak of this hormone during the night and reducing it in the presence of luminosity.
The process of melatonin production is as follows: the retina captures the presence or absence of light, passing this information to the optic nerve, then to the supraquiasmatic nucleus and from there to the upper cervical ganglion, which reaches the epiphysis. The epiphysis proceeds to carry out a series of reactions that culminate in the production of melatonin, which is distributed throughout the rest of the body. Apart from its birth in the brain, it also appears in the retina, liver, kidneys, intestine, immune cells and in the female endometrium.
Melatonin has its receptors at various points in the body , both inside and outside the brain, which produce different effects on the functioning of the body. The brain’s melatonin receptors have an effect on circadian rhythms, the non-neural ones influence reproduction, and finally the peripheral ones have different effects depending on their location.
Thus, the functions of melatonin are many and varied, affecting various systems of the organism, although the function for which it is best known and studied is that of controlling circadian rhythms , mainly carrying out a chronobiological action in the supraquiasmatic nucleus. In other words, this hormone helps to establish when we go from sleep to wakefulness and vice versa. The maximum production usually occurs around an hour and a half after falling asleep, helping to induce deep sleep.
Effects beyond Sleep
Apart from the function of regulating the sleep-wake cycle, recent research has shown that this hormone is very useful in many systems. It actively participates in the regulation of seasonal and reproductive phenomena, such as oestrus in animals. It also has an impact on long-term memory enhancement .
The immune system is also affected by this hormone (reducing its efficiency during its absence) and has an important antioxidant effect that counteracts the excess of free radicals. Thus, this hormone also participates in the processes of growth and aging.
Exogenous use of melatonin
Despite being an endogenous hormone, manufactured by the body itself, melatonin has been artificially synthesized and marketed as dietary supplement (although it is not yet allowed as a medicine due to the little research that exists and the inconclusive results extracted so far).
Some of the uses to which it has been put are as follows:
1. Sleep disorders
Melatonin has been used as a treatment for sleep disorders . Specifically, its capacity to improve the adjustment of sleep in cases of jet lag stands out , and it has been shown that when administered around bedtime at the point of destination, jet lag is considerably reduced. This is why it is widely used in circadian rhythm disorders. It also produces benefits in the case of delayed phase sleep syndrome, as well as in sleep mismatches in the case of individuals who work late at night.
However, with regard to primary or secondary insomnia to another disorder, although has shown to decrease sleep latency and improve the amount of time spent asleep , in some studies has not shown a greater effect than placebo, being more effective use of benzodiazepines and always prioritizing sleep hygiene.
Some research shows that the administration of this substance produces improvement in other disorders due to the improvement in sleep patterns, being examples of them cases of autism or childhood epilepsy. However, further research is needed.
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2. Action on reproduction and growth
It has been observed that melatonin administration is linked not only to sleep patterns, but also to other seasonal processes.
In animals, has been shown to affect and modulate oestrus periods . In humans, it has been observed that the administration of this hormone affects growth, making it evident that it has an effect at the time of the appearance of puberty. An excess of this hormone can delay it, while a defect can cause an advance of it.
Research indicates that melatonin supplementation may act preventively to prevent migraines .
4. Mood disorders
Different studies have demonstrated the efficacy of melatonin application to improve the condition of patients with depressive disorders, especially in the case of seasonal affective disorder.
5. Aging and dementia
The production of melatonin is not constant throughout life , producing a significant and progressive decrease from adolescence to the end of life (which helps explain why the elderly have shorter and more frequent periods of sleep).
In addition, a large part of the effects of aging are due to the presence of free radicals. Likewise, different types of free radicals and oxidation have also been linked to dementia processes such as Alzheimer’s or Parkinson’s.
Given that melatonin has been shown to be one of the major endogenous antioxidants available, several tests have shown that the administration of melatonin decreases oxidative damage in the different systems of the organism, and thus can be an aid to delay brain aging and prolong intellectual functioning in dementia.
The application of melatonin in some cancer patients seems to reduce tumor growth and prolong survival, being observed as a possible treatment to be combined with chemotherapy. This effect seems to be due to antiproliferative properties and to the potentiation of the effects of chemotherapy, especially in cases of cancers that depend on reproductive cells.
7. Other inconclusive research
As mentioned, melatonin has certain effects on the immune system, acting as a modulator . In addition to being a powerful antioxidant, it has been found to act on receptors in T-lymphocytes, contributing to the production of immunoglobulin.
It has been studied to help slow down the replication of HIV, so it could be applied as a booster treatment. Its usefulness in cases of different cancers has also been explored. However, the results are not conclusive.
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