Why you need to sleep completely in the dark

When in-depth sleep quality studies are conducted, there is no choice but to take participants to the laboratory and monitor them overnight while they sleep. Only in this way can all factors that can affect sleep duration, such as noise, temperature and especially light, be controlled.

For many years, common sleep hygiene recommendations were to sleep in a cool room (around 18 degrees), quiet and dark. But how much darkness do we need to sleep well? Recent research shows that the darker the room, the better.

Sleep and light phases

Our internal circadian clock, located in the brain, “sets the time” for daylight and darkness at night. When we watch TV or look at a cell phone screen before bed, we artificially lengthen the amount of time our eyes are exposed to light. This “toxic light” has long been proven to alter our sleep patterns and prevent us from falling asleep. Even screen light before bed can reduce the secretion of melatonin, the hormone we need to fall asleep.

But for people who sleep with lights or a TV on in the room, or sleep in a room with a window that lets in outside light, dim lighting at night can affect the quality of their sleep.

While we sleep, our brain goes through different stages of sleep:

These four phases are repeated in 90-minute cycles with short awakenings between one cycle and the next. Deep sleep tends to be longer at the beginning of the night, and REM sleep is longer at the end before we wake up in the morning.

When our sleep is disturbed by noise or in this case light, these small awakenings occur more often and we are unable to enter deep sleep. The result is poor quality sleep, which becomes less restful and causes us to wake up feeling tired.

Decreasing the duration of deep sleep has been proven to negatively affect health. Light at night, while shortening the duration of this phase, increases the time we spend sleeping in REM sleep, which is not necessarily a good thing if it comes at the expense of restful sleep.

Sleep with light and the nervous system

Recent research shows that even with your eyes closed, small amounts of light can disrupt sleep cycles, which has other effects on the rest of the body, such as blood sugar levels. Northwestern University in the US conducted a study with 20 participants aged 19 to 36 years, during which they were asked to spend two nights in a laboratory. The first night they slept in a very dark room. On the second night, half the group slept under a small light emitting 100 lux, an intensity similar to that of a television on or a street lamp coming through a window. The other half spent the second night in a dark room.

According to neuroscientist Phyllis Zee, author of a Northwestern University study on the effects of light on rest, “One night of exposure to moderate ambient light during sleep can alter glucose regulation and cardiovascular health.

Participants were hooked up to an intravenous tube that continuously drew blood samples while they slept, and their heart rate, brain waves and hormone levels were recorded. As a result, participants who slept in rooms with dim lighting spent less time in deep sleep, and their insulin increased by an average of 25% in the morning. High insulin levels are a sign that the body is unable to metabolize glucose. They also had higher than average heart rates. This has nothing to do with sleeping more or fewer hours, as a previous study noted that it was the quality of sleep during those hours that influenced blood sugar levels.

This change in blood glucose levels means that cells become temporarily resistant to insulin, which over time can lead to type 2 diabetes. According to neuroscientist Phyllis Zee, author of the above study, light is extremely powerful because it can sync rhythms and even get them out of sync. moment, can desynchronize them. As he explains, “one night of exposure to moderate ambient light during sleep can alter glucose regulation and cardiovascular health.”

In fact, there are previous studies that have proven that there is a link between light exposure during sleep and an increased risk of developing type 2 diabetes in older adults. In a study of more than 40,000 women, it was found that sleeping with the TV on or dim lights was associated with an increased risk of obesity, specifically a 17% greater chance of gaining five kilograms over the next five years.

Why sleep in the dark

What happens is that the body is activated and we go into a state of readiness when there is light, even while we are sleeping. This phenomenon is called sympathetic activation because it is the sympathetic autonomic nervous system that kicks in, increasing heart rate, blood pressure, and blood sugar levels as if it were preparing us for action (which it is not). case occurs). Chronic heart palpitations and tension at night can increase the risk of cardiovascular disease.

How much light is too much light? This 100 lux indicates that there is enough light so that when we wake up at night, we can easily move around the room. In fact, the room should be dark enough to make it difficult to see objects. Neurologist Daniela Grimaldi, co-author of the Northwestern study, states that “even if you are sleeping, your autonomic nervous system is activated. Badly. Typically, heart rate and other cardiovascular parameters are lower at night and higher during the day.”

When there is light, the body is activated and we enter a state of readiness, even when we sleep. This phenomenon is called sympathetic activation.

The authors of the aforementioned Northwestern study recommend a number of simple steps to help improve our sleep by avoiding light:

*Dario Pescador is editor and director of Quo magazine and author of the book. your best personality Author: Oberon.