July 15, 2024

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Even a little light during sleep can be bad for your health

Even a little light during sleep can be bad for your health


Even a little light during sleep can be bad for your health.

We all turn off the lights and draw the curtains before going to bed, and researchers recently found more scientific evidence for this seemingly common-sense practice.

Many Americans sleep with some kind of artificial light in their room, such as a TV, electronics, or streetlights outside the house.

But even one night’s sleep in moderately bright light can adversely affect cardiovascular and metabolic health, according to a new study.


Sleep is vital to the relationship between emotion and memory



“What surprised me was that even a tiny bit of light that passed through the eyelids and into the brain had a noticeable effect,” said Phyllis Zee, Ph.D., senior author of the study and director of the Northwestern University Center for Circadian Rhythm and Sleep Medicine.


In addition to this, there is growing evidence that exposure to light at night can cause a variety of harm to the body or increase the chance of developing chronic diseases.




Physiological effects of light

Dr. Zee and her team at Northwestern University conducted a small study of 20 subjects to analyze the effects of 100 lumens of artificial light on healthy adults during sleep.


“In this light, you can still see things around you, but it’s not comfortable to read.” In the study, all subjects slept in an almost dark room on the first night.

On the second night, half of the subjects slept in a brighter room. (The light source is above the head.)


While the subjects slept, the researchers recorded their brain waves and heart rate, and drew blood every few hours, among other tests.

After waking up in the morning, subjects in both groups consumed large amounts of sugar and observed how their bodies responded to the sugar surge.


The results showed that there were significant differences between the two groups of subjects.

The subjects who slept in the light had higher heart rates throughout the night and greater insulin resistance in the morning, meaning they had a harder time keeping blood sugar within the normal range.



Light can interfere with metabolism

Dr. Zee pointed out that falling asleep in a light environment at night can cause a variety of metabolic disturbances.


Although studies have pointed out that light can interfere with sleep quality, surprisingly, this study did not find this during the monitoring process.

In fact, most of the subjects said they slept well.


The researchers also measured melatonin levels in the subjects. This hormone helps regulate the circadian rhythm and promotes sleep, with low levels during the day and high levels at night.

Studies have shown that exposure to artificial light at night can inhibit the secretion of melatonin.

Scientists have also found that there is a correlation between melatonin disturbance and a variety of diseases, such as cancer, diabetes and so on.

However, the study also did not find a decrease in melatonin levels in subjects who fell asleep with light.


“This may mean that the light entering the eye is not bright enough to suppress melatonin secretion.”


But Dr. Zee and his team believe that such a small amount of light is enough to activate the sympathetic nervous system of the autonomic nervous system, which regulates the body’s “fight or flight” response. During sleep, the system is supposed to “cool down”, switch to the parasympathetic nervous system, and the heart rate and respiration rate drop with it.

But changes in the subjects’ cardiovascular function showed that even a small amount of light was enough to switch the nervous system to a more active and alert state.


“It’s like the brain and heart know the lights are on.”


Dr. Chris Cowell, who studies the mechanisms of circadian rhythms at the University of California, Los Angeles, pointed out that this study shows that even relatively dim light can interfere with our sleep-wake cycle.

He thinks the findings make sense because the autonomic nervous system obeys a stable circadian rhythm.


“In order for us to get a good night’s sleep, the body performs many coordinated actions, and these are regulated by the balance of the autonomic nervous system.”

While the effects of light on the nervous system are not as pronounced as when awake, Dr. Cowell noted that the disturbance is still a cause for concern. “If you want to get a good night’s sleep, this effect can be avoided.”



Increased risk of chronic disease

The findings of this study are not big news. Cowell pointed out that there have been many studies showing that disruption of the circadian rhythm can affect the body’s regulation of blood sugar levels.


In some of these human experiments, the light used in the study was much brighter, and the subjects were not actually asleep. While the study’s findings cannot predict long-term effects, Cowell suspects that these harmful effects will accumulate over time. “It’s just one night, imagine what it would be like if it went on like this for a long time?”


The body’s “master clock”, called the suprachiasmatic nucleus, is located in the brain, but organs and tissues throughout the body have their own cellular “timers.” Pancreatic cells responsible for secreting insulin are one such example. Interfering with the sleep-wake cycle affects its ability to normally secrete insulin, which in turn affects the body’s regulation of blood sugar.


“This increases the risk of chronic diseases such as insulin resistance, diabetes, and other cardiometabolic problems,” said Dr. Charles Zeissler, a professor at Harvard Medical School.


For example, a large observational study of more than 40,000 women found that sleeping with the TV or lights on had a 17% chance of gaining 11 pounds over a five-year observation period. ).


Zeissler himself has carried out research to examine the longer-term effects of disrupted circadian rhythms on metabolism.

In a recently published study, he and colleagues concluded that during the three-week study period, the negative effects on subjects’ metabolism were primarily due to disturbances in circadian rhythms, and not necessarily sleep deprivation.


“Without increasing the level of artificial light at night, we found no adverse effects of chronic sleep deprivation on blood glucose metabolism.”


Of course, this does not mean that lack of sleep is not harmful to health, just to highlight the long-term effects of light exposure during nighttime sleep.


“People might think that as long as they’re asleep, the light won’t have any physiological effect. But that’s not the case.”






Even a little light during sleep can be bad for your health.

(source:internet, reference only)

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