Sleeping with a light can hurt health, study finds

‘People think that as long as they fall asleep and are unconscious, it’s not having physiological effects, but that’s simply not true’

A new study has found that just one night of sleep affected by a moderate amount of light could have negative effects on cardiovascular and metabolic health.

Study author Dr Phyllis Zee at the Center for Circadian and Sleep Medicine at Northwestern University told NPR that she “was surprised that even this fairly, I would say, small amount of light just getting through the eyes to the brain still had such notable effect”.

The results of the study concur with broader research coming to similar findings showing that exposure to small amounts of light during sleep can make people more susceptible to chronic diseases.

The study, which included 20 people, was set up to measure the effects of 100 lux of artificial light on healthy adults during sleep. “This is about enough light that you could maybe see your way around, but it’s not enough light to really read comfortably,” Dr Zee told NPR.

All of the subjects slept in an entirely dark room for the first night. The following night, half of the participants slept in a more lit room with the light placed above them.

The researchers recorded the test subjects’ brainwaves, heart rates, and took blood samples every few hours, in addition to other measures.

Both groups received a large amount of sugar in the morning to see how they responded to a spike in their sugar levels.

The study showed that those sleeping in moderately light conditions had higher heart rates through the night as well as increased insulin resistance the following morning, having more difficulties getting their blood sugar to normal levels.

Dr Zee said light exposure could affect your metabolism in several ways. While the participants sleeping in the lit conditions thought they slept fine, the researchers believe that the light was enough to affect the nervous system to go into a more alert and activated state.

“It’s almost like the brain and the heart knew that the lights were on, although the individual was sleeping,” Dr Zee said.

Dr Chris Colwell at UCLA told NPR that “there’s a lot of coordinated actions that have to occur in order for us to get a good night’s sleep and the autonomic nervous system balance regulates that”.

While the effects aren’t “dramatic”, Dr Colwell added that “you don’t want that going on when you’re trying to get a good night’s sleep”.

“This was only one night, so imagine if you’re living that way constantly?” he noted.

Disruptions to the body’s sleep-wake cycle can affect the ability of cells to release insulin, which in turn can affect blood sugar levels.

“That’s going to increase the risk of chronic diseases like insulin resistance, diabetes and other cardiometabolic problems,” Harvard Medical School professor Dr Charles Czeisler told NPR.

A 2019 study of 40,000 women found that sleeping with a TV or a light on was connected to a 17 per cent increased risk of gaining 11 lbs (5kg) over the course of five years.

Dr Czeisler alongside other researchers recently found that negative effects on the metabolism of participants during a period of three weeks were caused more by disruptions to the circadian rhythm, rather than by sleep deficiency.

“When we did not increase their exposure to artificial light at night, we did not see adverse effects of chronic sleep deficiency on glucose metabolism,” he told NPR.

“People think that as long as they fall asleep and are unconscious, it’s not having physiological effects, but that’s simply not true,” he added.