Walk and sleep. How sunlight affects sleep

A good night’s sleep starts with waking up in the morning, says Sean Stevenson, author of Healthy Sleep. It sounds strange, but it’s a fact: what we do during the day directly affects the way we sleep. For example, the amount of time we spend in the sun. How are these processes related and how can knowing about them help us get better sleep? Let’s try to figure it out.

Why is the circadian system needed?

Our sleep cycle is governed by the alternation of light and darkness. In science, this is called the circadian synchronization system. It can be compared to a clock built into our body: the circadian system helps control digestion, the immune system, pressure, appetite and mental energy. The suprachiasmatic nucleus, a small group of cells located in the hypothalamus, is responsible for its work. At a certain time, the circadian system sends a signal to the body that it’s time to sleep, and it produces the appropriate hormones.

This is how the daily biorhythm of a person who sleeps from 22:00 to 6:00 looks like

How does lighting affect sleep? As soon as it becomes light around us, the hypothalamus and all organs and glands associated with it receive a signal: it is necessary to wake up and be alert. Exposure to sunlight triggers the release of daytime hormones and neurotransmitters that set our biological clock. The main ones are serotonin, melatonin and cortisol.

Sleep and serotonin

We know that serotonin is one of the hormones of happiness. It turns out that he is responsible not only for a sense of well-being, but also for setting the body’s internal clock.

About 95% of serotonin is found in the gastrointestinal tract. And its secretion depends on the diet, the level of physical activity and the amount of light that we receive during the day. Special light-sensitive receptors in the retina send information to the hypothalamus: if our internal clock is set correctly, this process goes on smoothly day after day.

In the modern world, we often do not feel a lack of natural light – it is increasingly being replaced by artificial lighting.

Even in the most cloudy weather, street light is 10 times brighter than room light.

One study of office workers showed that those who sat by the window received 173% more natural daylight than others, and their nights sleep was 46 minutes longer.


Melatonin is not a sleep hormone because it does not induce sleep by itself. However, it directly affects the quality of sleep, creating the conditions in the body suitable for this.

Melatonin is produced by the pineal gland in the brain and other tissues that send the sleep signal to the cells. This happens naturally at nightfall, but we can prevent it if we don’t get enough light at the right time of day.

Cortisol instead of coffee

Cortisol is another hormone that our circadian system needs to synchronize sleep. In the book, Sean Stevenson quotes naturopathic doctor Alan Christianson, who compares cortisol to a coffee machine. In the morning we wake up because the adrenal glands have prepared a fresh portion of this hormone. And in the evening we fall asleep, because its reserves have run out.

The dependence of the level of cortisol in the body on the time of day

Sometimes cortisol is at its peak when it should be lowered, and vice versa.

You are probably familiar with the state when you feel physically tired in the late evening, but cannot sleep. Or when in the morning, instead of feeling refreshed, you barely leave your bed. All of this suggests that cortisol is being released at the wrong time.

Sunlight also affects the secretion of cortisol. This is explained by evolutionary biology: in the daytime, our ancestors were able to more actively obtain food and maintain a habitat. Interestingly, in sunny weather, the level of cortisol decreases more in the evening than in cloudy weather.

Program of action

Here are some tips from Sean Stevenson on how to use walks and sun exposure to help you sleep well.

Tip 1: go out in the sun at a good time

Our biological clock is most sensitive to sunlight from 6:00 to 8:30. During this time, exposure to the sun is most beneficial. And the best effect can be achieved if you are outside for at least half an hour.

Tip 2: take breaks

Take advantage of every opportunity to be in natural light: take breaks from work for 10-15 minutes to go outside, hold meetings in the fresh air, or at least stand by the window more often.

Tip 3: use sunglasses with care

Sunglasses protect our eyes from hazardous radiation, but at the same time block the natural light needed for hormones to be produced properly. If you decide to wear glasses, make sure they are with high quality UV protection. Low-quality glasses let in even more dangerous radiation, while keeping your pupils wide open.

Tip 4: get light beyond the window

Getting sunlight from a window is not very helpful. Glass transmits harmful UVA rays that increase the risk of skin cancer and blocks UVB rays that compensate for the former.

Tip 5: use gadgets that simulate sunlight

In extreme cases, if you do not have the opportunity to be outside at all, you should get gadgets that simulate sunlight: backlit tables, special visors. However, remember that while all of these devices have been clinically proven to be useful, they will not replace a short walk, even in the most cloudy weather.

Based on the book “Healthy Sleep”

Cover photo from here

#Neurobiology #Energy

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