Whether it’s shop windows, illuminated street lamps and billboards, or home electronics, ambient night light is everywhere. Light pollution accused of disturbing the landmarks of animals and playing a role in the disruption of circadian rhythms in humans.
This shift in the biological clock can affect health and promote weight gain in particular. Artificial light at night also increases the cardio-metabolic risk. But the mechanisms involved in this latter process have so far not been well described. American researchers from Northwestern University therefore wanted to know more about the issue. For this, they studied the sleep of 20 healthy adults, aged 18 to 40, by comparing the effects of moderate exposure (100 lx) to light during sleep with those of a dimly lit environment ( <3 lx). And the results published in the Proceedings of the American Academy of Sciences (PNAS) are unequivocal.
A light that harms the rest of your heart
As the researchers point out, “in modern societies, exposure to indoor and outdoor nighttime light has become common, whether from screens or from sources outside the home, especially in large urban areas. It is also estimated that around 40% of people sleep near a light source.. A deleterious phenomenon for health. Indeed, these scientists have shown that moderate exposure to light during sleep is detrimental to heart health.
Sleeping in a lighted room, even with moderate light sources, puts the body on alert. The heart cannot truly rest, which increases the risk of heart disease. Moreover, when sleep is exposed to 100 lux (moderate light) versus 3 lux (low light), the heart rate accelerates, via the activation of the sympathetic nervous system. So the heart gets tired. As a reminder, the sympathetic nervous system is especially activated during the day, especially in the event of danger and fear, which is why it increases blood pressure. Unlike the parasympathetic system, which normally regulates our organs at night when the body is regenerating, it also promotes the release of glucose from the liver.
A higher risk of diabetes
In addition to heart health, which is directly affected by this light pollution, the pancreas is also affected. Based on the same light levels, scientists indicate that sleeping in even a moderately lit room increases the risk of diabetes. And for good reason, insulin resistance is observed the next morning a night’s sleep exposed to moderate light. As a result, the pancreas makes more insulin with a longer term risk of increased blood sugar levels.
If the metabolic changes are not in doubt for the researchers, the participants are not aware of them and do not feel the effects directly. The only thing that could alert would be fatigue since “the brain then behaves as during a sleep is light and fragmented. The physiology of sleep does not calm down as it should”says Dr. Daniela Grimaldi, neurologist and researcher at the Center for Circadian and Sleep Medicine at the Feinberg School of Medicine. Sleep is therefore not restorative.
One night is enough
A single night’s sleep exposed to moderate nighttime lighting can impair blood sugar and cardiovascular regulation, and exacerbate these risk factors for heart disease and diabetes, researchers say. “This study provides insight into the physiological mechanisms underlying the relationship between nocturnal light exposure, particularly during sleep, and cardiometabolic function.”explain the scientists.
These therefore recall some principles to promote sleep and improve the quality of sleep. Turn off all the lights or, failing that, put a dimmed one (red or orange), less stimulating for the brain, on the ground. When light seeps in even through shutters or curtains, wear a mask over your eyes to block out any source of light. The message from the researchers is clear:if you can make out things just fine, it’s probably too bright. Close the blinds, draw the curtains and turn off all the lights before going to bed “.
Finally, banish all white or blue light. In this regard, the naturopath Stéphane Tétart whom we interviewed in the second episode of our podcast “In your dreams”, explained that it was important not to use your smartphone during the hour before bedtime.
The effect of light in case of white night
“This study also showed that a full night of sleep deprivation with nocturnal light exposure increased insulin and glucagon-like peptide-1 levels, increased insulin resistance, and reduced nocturnal melatonin.”. So many changes that “have not been observed under dark sleep deprivation conditions “. Clearly, to sleep well and take care of your health, at night, bet on darkness!