Last Updated: Mar 16, 2022

According to a recent study, sleeping for only a single night with dim light, such as a television with the volume turned off, increased blood sugar levels and heart rate of young, healthy people participants in a sleep lab experiment.

The dim light goes in the eyelids and disturbs sleep, although the participants sleep with their eyes closed, stated Dr. Phyllis C. Zee, Director, Center for Circadian and Sleep Medicine at the Feinberg School of Medicine, Northwestern University, Chicago.

Heart rate typically falls during the night, slowing because the brain rejuvenates and repairs the body. A higher heart rate at night has been proven in many studies to be an indicator for early death and heart disease.

A high blood sugar level is an indicator of insulin resistance. The body cannot utilize glucose effectively and the pancreas shifts into overdrive, flooding the body with more insulin until it loses the ability to perform this task.

Eyes Closed While Sleeping:

Research has previously shown a link between artificial lighting at night, disruption in metabolic function, weight gain and obesity, cardiovascular risk factors, insulin production, and the development of diabetes.

Phyllis C Zee asked, “Why would sleep with your lights on affect your metabolism? Could that clarify why there is a higher prevalence of obesity or diabetes in society?”

Phyllis and her team gathered 20 healthy people in their 20s and told them to stay in the sleep lab for two nights. The first night was spent in a darkened room where “you would not be able to see anything, even when your eyes were open,” Phyllis Zee stated.

All the participants in the sleep lab were connected to the devices, which monitored several objective measures of sleep quality. So the participant’s data could be collected with minimum interference; participants slept on their bed with an IV, the long tubes that ran all over the bedroom and via a hole on the researcher’s side of the laboratory. The blood collects without touching the sleeping participants.

“We recorded brainwaves and could determine the stage of sleep the person was in,” Phyllis stated. “We monitored participant’s EKG, breathing, heart rate, and also collected blood from them to test the levels of melatonin while they were asleep.” Melatonin is a hormone produced mainly by the pineal gland during the night and has long been linked to sleep-wake regulation.

A random part of the group repeated that same lighting level for the second night in the sleep lab. In contrast, another group of participants slept under a dim overhead light with a glow similar to “an extremely dark, cloudy day or street lights coming through a window,” Phyllis Zee stated.

“Now the people were sleeping with their eyes closed,” Zee explained. “In the literature, the assumption is that around 5 to 10 % of light in the environment would pass through the closed eyelids, which means it is not much light.”

However, even that little bit of light led to a loss of slow-wave and fast eye movement sleep. Zee stated these are the phases of rest during which the most cellular renewal occurs.

Furthermore, insulin resistance increased, heart rate rose, and parasympathetic and sympathetic nervous systems were not balanced, which has been associated with higher blood pressure in a healthy person.

The light was not bright enough, but enough to decrease melatonin levels in the body, Zee said.

What should you do while Sleeping?

What suggestion could Phyllis Zee give people based on existing research and study in the field? Close your curtains and blinds, use a sleep mask, and turn off all lights.

“I believe that the most convincing evidence is that you should pay attention to the light in the bedroom,” Phyllis stated. “Make sure you start dimming the minimum of the light for one hour or two before going to sleep to make sure that you are in a good place for sleeping.”

If night light is required, then keep it dim and at floor level “so that it is more reflected rather than directly close to your eyes or above your bed,” Phyllis suggested.

Also, be conscious of the kind of light you are using in your bedroom, she advised, and you should also remove any light sources that fall in the blue spectrum, such as those produced by electronic devices such as tablets, smartphones, TVs, and laptops, etc.

“Blue light is the most stimulating form of light,” Zee said. “If you need to keep the light on for security reasons, you should change the light color. It is best to select light bulbs with more brownish or reddish tones.” Phyllis stated.