- Raquel Sánchez Varo, Diego Teófilo Bermúdez Flores and Juan Antonio López Villodres
- The Conversation*
It is true that there are few things more pleasant than a restful sleep after “falling into the arms of Morpheus.” Now, another great truth is how annoying it is to “spend a night awake.”
Sleeping well is one of the physiological processes with the greatest impact on our daily wellness. In fact, long-term lack of sleep has negative effects on our health.
Sleep is regulated by the combination of two processes. On the one hand, circadian rhythms. On the other, the accumulation of sleep-inducing substances in the brain, such as adenosine. Its quantity depends on several factors. Among others, the time we have been awake (longer, more adenosine) or the quality of sleep.
Our circadian rhythm controls the so-called sleep-wake cycle, divided into a rest phase (dark-sleep) and an alert phase (light-activity). That is why it is related to our behavior throughout the day.
The circadian (“near day”) clock in our species lasts for about 24 hours, and the body needs to synchronize it with environmental signals. The most important external synchronizer of our biological rhythm is the light-dark cycle.
The watchmaker or synchronizer of our biological clock
The pineal gland or epiphysis is a chronobiotic agent. This means that synchronizes our internal clock with the light-dark cycle. In the absence of light, this small brain organ of only 120 milligrams produces the hormone that leads us to the world of dreams: melatonin.
In some animals (fish, reptiles and amphibians) this gland is located under the skin and is capable of receiving light information directly. Hence it is also known as “the third eye.”
However, in the human species, as well as in most vertebrates, this pineapple-shaped, pea-sized organ it is located inside the skull. Therefore, you need more complex ways to know if it is day or night.
The retina records the light information, which reaches the suprachiasmatic nucleus (SPQ) of the hypothalamus (see diagram).
This is the brain structure responsible for controlling the circadian rhythm as a biological clock. The nucleus informs the pineal gland, the star of this process, to synthesize and release melatonin in dark conditions.
When our internal clock becomes out of sync with the rhythms of the environment, it triggers a conflict.
This is what happens, for example, when we make a trip whose origin and destination have different time zones (transoceanic), triggering the famous jet-lag or jet lag syndrome.
In these cases, a phase of adaptation to the new rhythm acquired is necessary, more difficult if we travel to the east, due to the loss of hours that it entails.
Sometimes taking melatonin tablets is used to synchronize with the new schedule.
Another example are shift work, in which the light-dark cycle is altered.
During the night there is an artificial exposure to high light conditions that inhibits the production of melatonin, confusing this system.
These situations could cause sleep disturbances and other harmful effects.
Such effects occur since melatonin not only plays a fundamental role in inducing sleep, but also has a hypotensive and inhibitory effect on thyroid activity.
As if that were not enough, this night owl hormone is also a antioxidant agent, neuroprotective, immune system modulator and oncostaticas it controls the development of tumors.
In fact, the International Agency for Research on Cancer (IARC) has classified night work shifts as “probably carcinogenic to humans” (the so-called group 2A). There are several studies that point to a higher incidence of breast cancer in women who work rotating shifts for long periods of time.
Even sexual behavior is affected by melatonin, whose levels rise in autumn and winter due to the lengthening of the nights. This produces an ovarian and testicular atrophy that decreases the production of sex hormones. Therefore, sexual and reproductive activity is reduced. These effects are most evident in seasonally breeding animals.
Finally, it has been described that in periods of low light there is a higher incidence of depressive disorders. This is the case of seasonal affective disorder, more frequent in more northern latitudes.
The importance of sleep hygiene
It is important to note that certain serious sleep disturbances are related to some mental illnesses. Also that insomnia is a risk factor to develop depression. However, the mechanisms underlying these disorders are quite complex and depend on many other factors.
What is evident is that proper sleep hygiene is essential for our physical and mental well-being. To this end, the World Sleep Society (WSS) proposes a list of ten simple recommendations. These include setting a sleep schedule, monitoring caffeine intake, or exercising regularly.
Once the relationship between luminosity and mood is known, we could say that Descartes was not misguided when he referred to the pineal as the very “seat of the soul”. According to the philosopher, from this remote place, in the center of the brain, the soul would direct the relationship between the body and the mind.
It is possible that this very spiritual observation is related to dimethyltryptamine (DMT), a substance with hallucinogenic properties produced in the pineal and also used as a dangerous drug of consumption. For this reason, DMT has been called the “drug of the gods” and has been associated with near-death experiences.
* Raquel Sánchez Varo is an assistant professor in the Histology Area of the Faculty of Medicine. Researcher at the Center for Networked Biomedical Research in Neurodegenerative Diseases (CIBERNED) and at the Malaga Biomedical Research Institute (IBIMA), University of Malaga.Diego Teófilo Bermúdez Flores is full professor of Histology. Teaching Unit of Histology and Pathological Anatomy. School of Medicine. University of Malaga, University of Malaga.Juan Antonio López Villodres is a professor contracted doctor of the Area of Histology of the Faculty of Medicine of Malaga. Member of research groups of the Ministry of Innovation, Science and Business of the Junta de Andalucía and IBIMA., University of Malaga.
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Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.