Sleeping with ambient light in your room bad for your health, says new research

Time to deploy the blackout blinds

A woman in bed wearing a sleep mask
(Image credit: Pexels / Polina Kovaleva)

If you live in an urban area, it's not unusual to have some amount of artificial light creeping into your room overnight. Even if that's not the case, many choose to have a nightlight, hallway light, or TV on overnight. But if the results of a new study are anything to go by, it's time to switch off that bedside lamp and invest in some blackout blinds.

Research has found a link between exposure to ambient light while you're trying to sleep at night, and adverse health effects. In the study, even one night of 'moderate' light exposure was found to impair glucose and cardiovascular regulation the following day, which in turn increases risk for conditions such as heart disease, diabetes and metabolic syndrome.

In the study (opens in new tab), scientists asked a group of 20 young, healthy adults to sleep in rooms with dim light, and with overhead light, and monitored sleep quality, heart rate and heart rate variability, insulin resistance and melatonin levels. Sleeping in the light room resulted in increased insulin resistance in the morning, and a higher heart rate and lower heart rate variability overnight. Insulin resistance means your body can't turn the glucose in your blood into energy, which in turn prompts your pancreas to create more insulin, leading to higher blood sugar levels over time.

"The results from this study demonstrate that just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes and metabolic syndrome,” senior study author Dr Phyllis Zee told Northwestern University (opens in new tab). "It’s important for people to avoid or minimise the amount of light exposure during sleep."

Exposure to light and dark plays a key role in prompting certain biological functions. Northwestern University explains that exposure to light causes our heart rates to increase in order to increase alertness during the day. Phyllis suggests that the study shows the body is responding in a similar way when exposed to light overnight, with your sympathetic nervous system kicking in when it should be your parasympathetic nervous system taking charge (the latter is what helps with restoration). 

Ruth Hamilton
Ruth Hamilton

Ruth is T3's Outdoors editor, reviewing and writing about everything from camping gear and hiking boots to mountain bikes, drones and paddle boards. To counter all that effort, she also runs the site's Wellness channel, which includes sleep, relaxation, yoga and general wellbeing. She has tested more mattresses than her small flat can handle, and has had to implement a one-in-one-out pillow policy, for fear of getting smothered in the night.