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In the dark you sleep better and fight cardiovascular disease, diabetes and obesity

In the dark you sleep better and fight cardiovascular disease, diabetes and obesity

April 11, 2022
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Do you want to rest well at night and avoid increasing the risk of cardiovascular disease, obesity and diabetes? Then turn off all the lights and close the curtains tightly! In fact, sleeping in a room that is lit, even by external lights such as neon signs or street lamps, does not allow the body to relax, cardiovascular stress increases and the next day there is greater resistance to insulin. This is what emerges from a very recent scientific research published in the prestigious PNAS journal thanks to the work of an American team from Northwestern University (Mason et al, PNAS, March, 2022).

Our internal clock

Concentration, heart rate, use of insulin, appetite, energy, mood and body weight, all of this is defined by our internal clock. This clock establishes the alternation of the sleep-wake rhythm, puts the body in a condition to rest and regenerate itself during the night and increases the sense of alertness during the day. This fascinating mechanism is regulated by hormones that are released according to the conditions of light or darkness, following the alternation between day and night. When this balance is altered, for example when we are exposed to too many lights in the evening hours, our biological clock is jammed and some processes in our body no longer work as they should with consequences for health. Previous studies had observed that those who sleep in a lighted room have a greater risk of developing obesity. However, to date, it had not been possible to understand the exact causes of what was observed.

Why it is important to sleep in dark rooms

To better understand the action on the health of the lighting in the room where you sleep, the American researchers have developed the study we are talking about today. 20 volunteers were recruited. The study participants were divided into two groups. The first group was asked to sleep for two nights in dark conditions and the third night in a room where light was filtering through. The light made it possible to distinguish the objects inside the room. The second group has always slept in dark conditions. Volunteers were monitored both during the night and upon awakening. What emerged was that sleeping in rooms with a moderate lighting caused an alteration in the structure of sleep. Although the volunteers did not notice anything, their sleep had fewer deep and REM sleep phases and more light sleep phases. However, if the volunteers had not registered any difference the next day, their brains did and were activated as if in the presence of fragmented sleep. As a result, the sympathetic nervous system, the part of the autonomic nervous system associated with the waking phases, was stimulated and the heart rate increased. At the same time, the researchers found a decrease in heart rhythm variability. A high variability of the heart rhythm is a sign of health as it means that the cardiovascular system is better able to respond to stress. Lower variability indicates more difficult adaptation and an increased risk of cardiovascular disease. Not only that, the following day, those who had slept in the room with more light also had greater resistance to insulin. This means that the cells of muscles, tissues and liver are unable to respond correctly to insulin and to use circulating glucose to obtain energy. The body responds by increasing the release of insulin but in the long run this is not enough and blood sugar increases, opening the doors to type 2 diabetes.


Therefore, to improve the quality of sleep and gain health by decreasing the risk of cardiovascular disease, diabetes and obesity, it is important to sleep in dark conditions. Close the blinds and curtains, turn off the lights and the television. Then, as indicated by the authors of the study themselves, if you really need to keep some night lighting for safety reasons, choose colors such as amber or orange, which are less stimulating, avoiding white and blue lights which instead activate the brain more. Then, try to place the light close to the floor and avoid it directly illuminating your face. As an indication, you should never be able to clearly distinguish objects in the room.

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