Diabetes linked to sleeping with lights on

Are you a lights off, or a lights on person? I’m talking, of course, about when you go to sleep. Some people like to keep a light on overnight, but now new research suggests it’s a bad idea and, instead, sleeping in the pitch black is better for your physical health. Naked Scientist Harry Lewis is a big fan of sleeping in total darkness...

Harry - I certainly do Chris. Ear buds out. Blackout curtains open. Ready for the day. That's right. New research coordinated by Phyllis Zee, chief of sleep medicine and department of neurology at Northwestern University, illuminates the health risk of sleeping with the light's on. I caught up with her, but when I did, she wasn't actually in Illinois.

Phyllis - I am in Rome right now. In Italy. In the eternal city.

Harry - It was the last place I went before the lockdown started to get put in place. It's quite a bright city. Although you are covered with the historic relics, there's a lot of light around.

Phyllis - There is a lot of light around in the center of Rome. I noticed that many of the ruins and beautiful historic sites are also lit at night. But the street lamps can be quite bright if they're right next to your window, especially when you're trying to sleep.

Harry - And that's what we're coming onto. A bit of research that you've probably recently, discussing the effects on our health if, when you are sleeping, you are in the presence of lighting. What are your findings from this research?

Phyllis - What we found was even in very healthy, relatively young people, having them sleep with their lights on compared to if they were able to sleep in much, much dimmer light, which was like less than three lux, that there was a difference. Those who slept in the room light had a higher heart rate throughout the entire sleep period, and the next morning, we challenged them with glucose. They drank a bunch of glucose and we found that the group that slept in the light condition had what we call 'insulin resistance'. That means that to keep their blood levels of sugar and glucose normal, the body had to secrete more insulin. That is what we see in, for example, people with type two diabetes. The tissue is less sensitive to the hormone insulin.

Harry - If we extrapolate this out, does that mean that if you were to sleep in the presence of light, not too much, but just a little bit, then this could result in somebody being more likely to be diagnosed with diabetes?

Phyllis - We know that having insulin resistance and increased heart rate during sleep, normally your heart rate should be going down during sleep, could be a risk factor for the development of what we call cardiovascular or metabolic disorders. There are other studies and one that was published just last year. What they found was that those who were sleeping with lights on during the night, whether it was from a lamp, a television, or outside light, were at higher risk for obesity.

Harry - I feel like because we've grown into this era of light being all around us. There must be a lot of research into the effects of light on our health when we are sleeping. Is that the case? Am I right in that assumption?

Phyllis - There's actually not as much research of light while we're sleeping. Most of our research has focused on light in the evening, usually before we go to bed. When you're awake, you're in bed and you're looking at your phone, you're looking at your light emitting devices. It's really more in that pre-sleep period. I actually was surprised. I don't sleep with the lights on, but there was a survey done in Britain that somewhere about like 30-40% people sleep with their lights on. I mean, that's a lot.

Harry - Yeah. I mean, I've got a little radio next to my bed and it actually pumps out probably enough light for me to just about see around. Maybe I should be turning that off before I go to bed.

Phyllis - Yeah. Especially the blue lights, your brain is gonna be much more activated by short wavelength or blue to green types of light than it would be for red or amber colours. I say sometimes people have to have their lights on for safety reasons, but think about changing that colour. Certainly if it's blue to something that's a little more on the red side. It can affect sleep. It can affect what you eat. It's really another modifiable factor that we can use to improve our health.