Researchers Nail Down Exactly Why You Should Avoid Light Before Bed

First Posted: Jun 30, 2017 08:42 AM EDT

Smartphone devices now have a blue light filter dubbed as "night mode" because excessive light before bed messes with our sleep. But why is that?

According to Caltech researchers, there's a protein in our brains that is programmed to react uniquely to lightness and darkness. This protein restores balance between wakefulness and sleep states.

Their findings are published in Neuron.

"Researchers had previously identified the photoreceptors in the eye that are required for the direct effect of light on wakefulness and sleep," says Prober, one of the researchers of the study. "But we wanted to know how the brain uses this visual information to affect sleep."

Zebrafish were the logical candidates for study participants. They are optically transparent, so viewing their neurons was easier. What's more, their sleep is similar to that of humans as they are awake during the day and asleep at night.

Wendy Chen, lead author, studied Prok2, a protein in zebrafish. In comparison to normal zebrafish, those with more Prok2 fell asleep during the day and were awake at night. This pattern was specifically related to light. In other words, if the lights were on, the overabundant Prok2 fish fell asleep and when it was off, they were awake. Interestingly, she found that genetically engineering fish with deficiencies in Prok2 were less active with the lights turned off and more active when turned on.

This is important. "Though diurnal animals such as zebrafish spend most of their time asleep at night and awake during the day, they also take naps during the day and occasionally wake up at night, similar to many humans," Prober says. "Our study's results suggest that levels of Prok2 play a critical role in setting the correct balance between sleep and wakefulness during both the day and the night."

What's more, the researchers discovered that Prok2 doesn't act alone to promote sleep when it's overexpressed and in the presence of light. Instead, gelanin, a sleep inducing protein, is needed. For example, gelanin was increased in the hypothalamus, the part of the brain that's focused on sleep, when there was more Prok2. Also, when gelanin was deficient, more Prok2 did not cause more sleep.

So, next time you take those last few glances at your computer or smartphone before bed, think about your Prok2 if you want a better night's sleep.

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