Sleeping for only one night with a dim light, such as a TV set with the sound off, raised the blood sugar and heart rate of healthy young people participating in a sleep lab experiment, a new study found.
The dim light entered the eyelids and disrupted sleep despite the fact that participants slept with their eyes closed, said study author Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg School of Medicine.
Heart rate typically drops at night, slowing down as the the brain is busy repairing and rejuvenating the body. An elevated heart rate at night has been shown in numerous studies to be a risk factor for future heart disease and early death.
High blood sugar levels are a sign of insulin resistance, where the body stops using glucose properly and the pancreas goes into overdrive, flooding the body with extra insulin to overcompensate until it eventually loses its ability to do so. Over time, insulin resistance can ultimately lead to Type 2 diabetes.
Sleeping with eyes closed
Prior research has shown an association between artificial light at night and weight gain and obesity, disruptions in metabolic function, insulin secretion and the development of diabetes, and cardiovascular risk factors.
“Why would sleeping with your lights on affect your metabolism? Could that explain why there is a higher prevalence of diabetes or obesity (in society)?” Zee asked.
Zee and her team took 20 healthy people in their 20s and had them spend two nights in a sleep lab. The first night was spent in a darkened room where “you wouldn’t be able to see much, if anything, when your eyes were open,” Zee said.
All of the study participants were connected to devices monitoring a number of objective measures of sleep quality. So data could be gathered with minimal interference, they slept with an IV with long tubes that snake across the room and through a hole to the researcher’s side of the lab. The blood was drawn without ever touching the slumbering participants.
“We recorded the brainwaves and could tell what sleep stage the person was in,” Zee said. “We recorded their breathing, their heart rate, their EKG, and we also drew blood from them to measure melatonin levels while they were sleeping.” Melatonin is a hormone that regulates the body’s circadian rhythm, or sleep and wake body clock.