The body's stress systems remain activated.
Are you among those who fall asleep to light from the bedside lamp or TV screen?
It may prove to have consequences for your health, according to researchers from the United States.
It is apparently not just light before bedtime that has something to do with our sleep. If you have the light on through the night, your body does not get optimal rest.
Rash after one night
The researchers tested the light effect during night sleep on 20 participants between the ages of 18 and 40.
They compared one night's sleep with moderate light (100 lux), and one night's sleep with dim lighting (3 lux) in a laboratory.
When we are exposed to light in the morning, our heart rate increases. This way we become more awake and ready to start the day.
- Our results show that a similar effect is also present when exposure to light occurs during night sleep, says Phyllis Zee, the author behind the study, in a press release.
Stress systems remain activated
Our heart rate and blood pressure are usually lower at night than during the day.
However, with four 60W incandescent lamps in the room, these continued to be activated in the study participants.
And with increased heart rate through the night, participants had increased insulin resistance the next morning, according to the study published in the journal PNAS.
The researchers found this out by giving both the participants and a control group sugar water. Those who had slept with the light on had higher insulin levels.
- Increased heart rate indicates that the body's stress systems remain somewhat activated through the night. This in turn affects the body's response to insulin, says Rune Enger, associate professor of medicine at the University of Oslo.
This causes the tissues in the body to have difficulty absorbing sugar from the blood.
In the long term, such a failure in blood sugar regulation can predispose to type II diabetes, Enger says.
A relatively large effect
Enger believes that the study is good and that it controls too many factors.
He points out that sleep studies are often based on self-reported information. This study, on the other hand, is experimental.
- Instead of mapping how people sleep, for example with a questionnaire, you take a group here and check both brightness, amount of sleep, and a number of other factors, while studying in quite detail how the participants sleep, he says.
The experiment showed that there was a relatively large effect after one night's sleep in a bright room.
Weaknesses of the study
A weakness with the study is that the study is precisely about one night's sleep.
- What is not mapped here is how it behaves if you often or always sleep with light in the room. You can imagine that you get used to the light exposure, he says.
- If this is not the case, and the body's stress system remains activated over several bright nights, these are important findings that should be followed up.
Furthermore, the study also addresses a small number of young, healthy, normal-weight individuals.
- It is conceivable that these are not so representative of people who are at risk of developing type II diabetes, he says.
More research is needed
Regardless, he believes that it is useful to be aware of what kind of light exposure one is exposed to. Light exposure both before and during sleep is associated with poorer sleep quality.