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HEALTH | 04.13.2020

J. A. Madrid, chronobiologist: “The use of mobile devices should be avoided one or two hours before going to bed”

Question: What is Chronobiology?

Answer: It is the science that studies the rhythms of life. It deals with all those biological phenomena that repeat with a certain cadence: every day, every month or every year. For example, daily sleep-awake, blood pressure and cortisol rhythms; or the annual rhythms of flu epidemics or child births. You could say that chronobiologists are the watchmakers of life.

Q: How does our biological clock work?

A: Our body contains a symphony of rhythms that play out in all our functions and behaviors, even if we are not aware of it. This music is orchestrated by a biological clock that sets our internal time and keeps our entire body in sync. Our internal time does not have to coincide with the time imposed on us by social obligations (social time). However, it does usually coincides with nature’s time, which is fundamentally driven by sunrise and sunset.

The system that generates internal time and keeps it in sync with nature’s time and social time is called the circadian system or biological clock. It acts as the conductor of the body’s orchestra and is found in the brain. It receives light information through the eyes and sends signals to the entire body. When we analyze a certain organ, such as the liver, we find it has its own clocks. Liver cells too have their own clocks. This complexity, together with the changing of environmental cycles and unhealthy life habits typical of developed societies, means that the biological clock is very easily altered.

Q: How does being in quarantine affect our biological clocks?

A: The confinement of people indoors in completely isolated environments has long been studied by chronobiologists. Without going into too much detail, last year we collaborated with the BBC on a documentary in which a volunteer stayed in a nuclear bunker for ten days. What we found was that every day he went to bed around half an hour later than the day before, but that he always did this with the same time interval. This signal to go to sleep, without consciously knowing what time it was, was provided by his biological clock.

As well as being such an extreme situation, coronavirus quarantine is a situation where many of our time indicators or social schedules have been lost. I am referring to working hours, school hours, etc. Therefore, if we want to prevent coronavirus from depriving us of sleep due to chaotic rhythms, we must adopt a rhythm whose primary objective is to bring back these lost rhythms.

Q: What are some sleep-related difficulties we may face?

A: The most common thing we see is difficulty falling asleep, caused by fear of getting sick or losing our job.

However, if we maintain regular schedules and incorporate a series of healthy habits, we may even sleep better than we did before. This is because we will be free to set a sleep schedule that best suits our personal chronotype.


“Lack of exercise has an impact on our sleep, metabolism and mood”

Q: How important is rest in the current context?

A: One way to “charge” your biological clock’s batteries is by making a distinction between what you do during the day and what you do at night. Daytime activity and nighttime rest are two sides of the same coin. Therefore, prioritizing rest at night is essential when it comes to feeling more invigorated the next day.

In order to fall asleep we have to guide our body and mind down a path of gradual disconnection: disconnecting from the news, switching to a warm low-power light, not eating dinner late, not exercising before bed and establishing relaxing routines before bedtime. During the day, it is worth giving our minds a rest from news and social networks by adding periods when we simply do nothing.

Q: These days a lot of people don’t have the option of getting out onto a terrace or into a garden. Is a lack of fresh air and natural light harmful?

A: The outdoors and exposure to natural light act as antidepressants and relaxants. Remember how you feel after returning home from a sunny day at the beach or in the countryside. Furthermore, natural light is the best synchronizer of our biological clocks. That’s why we should take advantage of any available moment to be near a window, let the sun into the house or go out onto the balcony or the terrace.


“The light from screens tricks our biological clocks by telling us that it’s not yet time to sleep”


Q: One of the few ways that we can interact with one another during quarantine is with cellphones or computers. Can excessive use of these devices take a toll?

A: Fortunately, most people have mobile devices that allow them to remain constantly in touch. However, this technology also has its downside. It can promote sedentary lifestyles, make us dependent on news and social networks, and increase exposure to screen light at night. Using mobile devices should be avoided or cut to one or two hours before going to bed. Light from screens not only activates our brains but also tricks our biological clocks by telling them it’s not yet time to go to sleep.

Q: What about a lack of physical exercise?

A: We are designed to move. Therefore, the less physical activity we do, the more we move away from this natural design. This then has a negative impact on our sleep, metabolism and mood. Quarantine means we have almost no choice in becoming more sedentary. This contributes to the deterioration of the biological clock and sleep.

Q: What advice would you give to someone who has noticed a deterioration in the quality of their sleep?

A: What I am going to say next applies to everyone, but especially to those who find that their sleep has worsened with quarantine. We need to work on three areas: habits, controlling information and life goals.

First of all, we must establish schedules for all of our activities: sleep, mealtimes, physical exercise, leisure and (virtual) social contact.

Second, we must try to allocate different times and places for work, rest and leisure. Starting the day with moderate physical activity (stretching, flexibility, yoga) and exposing ourselves to natural light, not working in bed, taking off our pajamas and putting on clothes as if we were leaving the house, taking advantage of every opportunity to move, and not spending too much time on screens are all good habits to adopt for confinement.

Third, it is important to set aside enough time for sleep and rest. It helps if we bring meal times forward (lunch before three and dinner at least two hours before going to bed), use warm lighting and disconnect from cellphones and tablets before bed.

Another problem that affects sleep is too much (often useless) information, and a growing number of hoaxes that prevent us from concentrating on other tasks that are more comforting and productive. Therefore, it may be useful to go on a “diet” where we consume less information.

Finally – and this is applicable regardless of the situation – I think it’s important that we avoid “killing time.” We should start every day with a goal that makes us wake up filled with energy. A month ago we were complaining that we didn’t have time to do the things we wanted to. Now might be the time to do them.


Ten habits for getting enough sleep during confinement

  • Sleep in the dark every night.
  • Get more than two hours’ exposure of natural light a day, preferably in the morning.
  • Stop using electronic devices at least two hours before going to bed.
  • Spend less than 10 hours a day sitting or being sedentary.
  • Perform moderate-vigorous activity at least 30 minutes a day, preferably in the morning.
  • Sleep between seven and nine hours a day and one or two hours more for adolescents and children respectively.
  • Don’t nap during the day for longer than 30 minutes.
  • At weekends, wake up at roughly the same time as you do on work days.
  • Eat dinner at least two hours before going to bed.
  • Eat breakfast every day.

Dr. Juan Antonio Madrid Pérez

Nutrition Specialist at the University of Granada (1985) and Chronobiology Specialist at the Pierre and Marie Curie University in Paris (1988). Dr. Juan Antonio Madrid PérezProfessor of Physiology at the Universities of Granada, Extremadura and Murcia. Professor of Chronobiology at the University of Murcia Faculty of Medicine. Full Professor of Physiology at the Department of Physiology of the University of Murcia since 1998. He has run the online Masters in Sleep: Physiology and Medicine since 2012.

Director of the Laboratory of Chronobiology of the University of Murcia since 1992 and Head of the Research Group of Excellence in Chronodisruption and Health in the Region of Murcia.