Sleeping on The Dark Side might be better than you think

Welcome to this edition's?Sleepletter?where we offer you easy-to-read insights from the latest research papers from the field of?sleep neurobiology?and clinical?sleep medicine. We hope you enjoy the content!

Sleep on The Dark Side

Do you know those moments when you fall asleep in front of the TV, laptop or smartphone while watching something just to wake up a couple of hours later not even realizing that you were going to fall asleep in the first place? I don’t know about you, but I certainly remember them. They may not seem to be all that bad for your sleep health since you at least slept a few hours in relative peace, right? Well, try thinking of it this way: you were asleep in front of a considerable light source – a screen. We know that the most important (but not the only) cue for your sleep/wake cycle is actually light. This tells the brain when you should be awake and when to go to sleep. The source could be sunlight, lights at home or light emitted by a TV screen. However, not all colors of light have the same effect on sleep. Blue light, which is beneficial during the day to boost our attention, concentration and mood is very disruptive at night. Blue light suppresses secretion of melatonin, a very important hormone for sleep and the circadian rhythm. Furthermore, artificial light at night, especially in industrialized countries, can also affect sleep. Studies showed that even a small amount of light at night can negatively affect your health and wellbeing, disrupt your?circadian rhythm and even increase the risk of obesity and cancer. Having read all of this, that supposedly harmless “nap” while watching TV late at night doesn’t seem so harmless after all. Since TVs or overhead room lights are quite strong light sources, could they have an effect on cardiometabolic health if left on at night? A new study published in PNAS has some intriguing answers for us.

Researchers from Northwestern University wanted to see the effects of dim and moderate light during sleep on cardiometabolic function, specifically glucose homeostasis and insulin resistance, both of which are important factors in diabetes. To test this, they recruited 20 young adults and separated them into two groups. One group of 10 slept one night in dim light and the following night in moderate light with overhead lighting turned on. The other group slept in dim light for both nights. But why not in complete darkness you might ask? Most people do not sleep in total darkness, with at least some ambient (e.g. moonlight) or street light coming through the window or blinds. Results from this experiment showed that people who slept with the overhead lights turned on had higher levels of insulin resistance, as well as higher heart rate after only one night compared to the group with dim light. Insulin resistance was positively associated with higher levels of sympathetic nervous system activity, indicating that glucose homeostasis might be impaired due to this. Although the differences in insulin resistance and heart rate were not huge between the groups, they might indicate that sleeping for months or even years with room lights turned on might slowly increase the risk of cardiometabolic disorders, but this still has to be proven. Melatonin levels were similar in both groups despite the room lights, but sleep architecture was somewhat different. People sleeping with the overhead lights turned on had less REM and slow wave sleep, which are important for memory, feeling rested the next day and many other processes. Overall, it seems that keeping the room lights on even for one day can have a small effect on cardiometabolic health which might accumulate over time and impair health which should people more aware that sleeping in front of the TV or laptop might not be the greatest idea for your health. This time, at least, you might want to choose sleeping on The Dark Side.

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About the author

Alen Juginovi??is a medical doctor and?postdoctoral researcher in the Department of Neurobiology at Harvard Medical School in Boston, MA, USA studying the effect of poor sleep quality on health. He is also organizing international award-winning projects such as Nobel Laureate conferences, international congresses, concerts and other, as well as participating in many events as a speaker. Feel free to contact him via LinkedIn for any inquiries.