Scientists from Northwestern University in the US found that even a night’s sleep in dim light increases blood sugar levels and heart rate.
Study participants were 20 healthy young adults who spent two nights in a sleep lab. On the first night, they slept in a completely dark room. While they slept, study participants were connected to devices that recorded indicators of sleep quality, particularly brain activity, breathing, and heartbeat. Also, before going to bed, the participants were placed in catheters to draw blood during sleep.
On the second night, the participants slept in a low level of illumination – as if street light had come from a window.
“According to the study, between 5% and 10% of light from the environment enters the eye through closed eyelids – not much,” the researchers noted.
However, even this was enough to complete sleep. The heart rate increased, insulin resistance increased, the work of the sympathetic and parasympathetic nervous systems was disturbed, pressure increased. At the same time, the light was not bright enough to reduce melatonin levels.
Researchers have warned that regular sleep in such conditions can be dangerous to health. They recommend dimming the lights two hours before bed, not leaving the lights on or the TV on at night, and also pulling the curtains tight or using a special sleep mask.