Researchers recently looked into the impact of light exposure during sleep on one’s health. They discovered that even one night of light exposure raises heart rate when sleeping and affects glucose metabolism the next morning. According to them, sleeping without exposure to light is probably good for cardiometabolic health.
At night, exposure to artificial light is widely used around the world and has been connected to detrimental health and well-being effects.
Northwestern University in Chicago researchers recently looked into the biological impacts of various degrees of light exposure during sleeping. They discovered that one night of sleep exposure to moderate ambient light can affect glucose and cardiovascular homeostasis, as well as raise risk factors for heart disease, diabetes, and metabolic syndrome.
A 2019 study indicated that artificial light at night (ALAN), such as from a nightlight or television, is associated with obesity in women. Light exposure during sleep may have a deleterious impact on metabolic control.
According to another study, when compared to low light exposure, blue-enriched light exposure in the morning and evening affects glucose metabolism and raises insulin resistance. Another study found that higher levels of ALAN are linked to higher rates of type 2 diabetes among older adults. The mechanisms underlying ALAN’s metabolic effects are unknown.
Sleep study
The scientists enlisted the help of 20 young adults for a three-day, two-night stay in the lab. They used actigraphy and sleep diaries to measure participants’ sleep habits a week before the study.
After that, the participants were assigned to one of two sleeping conditions:
- On the first night, participants slept with a dim light of less than 3 lux (lx), and on the second night, they slept with an overhead room light of 100 lx.
- On both nights, Sleeping in a dim light setting of less than 3 lx.
The participants supplied blood samples before and after food intake on Days 1 and 2 of the experiment to assess melatonin and blood glucose levels. They were also subjected to overnight polysomnography (PSG) test to determine the quality of their sleep.
Every two hours while awake, the participants completed surveys to assess their subjective drowsiness, appetite, and mood changes. Meanwhile, nurses took blood pressure and heart rate readings every hour and every four hours.
The researchers discovered that a single night of 100 lx room lighting raised heart rate during sleep and enhanced insulin resistance the next morning.
Participants exposed to 100 lx lighting during sleep had more N2 sleep — one of the deeper stages of sleep — and less slow-wave sleep — which is critical for memory consolidation — than those exposed to dim light. They also had less REM sleep, which is when you dream.
The researchers found no differences in melatonin levels or PSG-derived indices of cortical arousal, sleep fragmentation, or wake-sleep stage stability between the two groups. This could be due to the fact that only 5-9 percent of light passes through closed eyelids.
Underlying mechanisms
Phyllis C Zee, MD., Ph.D., the study’s corresponding author, said to Medical News Today when asked what could explain the link between ALAN and the observed effects on heart rate and glucose metabolism:
“There are potentially three possibilities. [The first is that light] can cause awakening or arousal. We found small changes [in these measures, but they did not] correlate with an increase in insulin resistance. So this is unlikely to be a primary mechanism.”
“Secondly, light can affect the circadian clock and affect melatonin secretion. However, we found no significant difference in melatonin levels,” Dr. Zee added.
“[We thus hypothesize] that light activates brain regions that regulate the autonomic nervous system because there was a relationship between the changes in heart variability and insulin resistance,” she explained.
Dale Sandler, Ph.D., was not engaged in the study and is a senior investigator and chief of the Epidemiology Branch of the National Institute of Environmental Health Services (NIEHS). “Subtle variations in sleep stages could [also] have a role,” Dr. Sandler concurred with Dr. Zee.
The researchers came to the conclusion that avoiding ALAN may be beneficial to cardiovascular and metabolic health.
What should I do?
What advice would Zee give based on her research and those of others in the field? Consider closing your blinds and drapes, turning off all the lights, and wearing a sleep mask.
“I think the strength of the evidence is that you should clearly pay attention to the light in your bedroom,” she said. “Make sure that you start dimming your lights at least an hour or two before you go to bed to prepare your environment for sleep.”
Remove any unnecessary light sources from your bedroom. If you must use a night light, keep it dim and at floor level, rather than immediately next to your eye or at bed level, so that it is more reflected. She also advised being conscious of the type of light in your bedroom and prohibiting any lights emitting in the blue spectrum, such as those generated by televisions, smartphones, tablets, and laptops.
“Blue light is the most stimulating type of light,” Zee said. “If you have to have a light on for safety reasons change the color. You want to choose lights that have more reddish or brownish tones.”
