Is checking a smartphone during the night bad for sleep?

A team of American scientists observed how the brain reacts to short, intense exposure to blue light in order to determine how sleep is affected.

Smartphones are now so integral to daily life that some people take them to bed.

However, several studies have shown that the blue light they emit has negative effects on health, especially sleep. A new study appearing in the journal eLife analysed the effects of short bursts of blue light on the sleep cycle.

"We all have smartphones, and their screens are very bright.

We're all getting exposed to light at the wrong times of day. It's becoming more important to understand how these different types of light information are relayed to the brain," said Tiffany Schmidt, Professor of Neurobiology at Northwestern University in Illinois, who led the research.

In order to better understand what happens in our brains when our eye focuses on the light of the smartphone's screen in the middle of the night, Prof. Schmidt's team worked with genetically modified mice whose specialised retinal cells (ipRGCs) affected only the suprachiasmatic nucleus, the structure in the brain regulating circadian rhythm.

LIMITING THE NEGATIVE EFFECTS OF BLUE LIGHT ON SLEEP

Because mice are nocturnal, they fall asleep when exposed to light. Those observed during this study, however, remained awake when exposed to short bursts of light during the night.

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The mice's body temperature, which is also correlated with sleep, did not respond to short amounts of light, suggesting that their overall circadian rhythms remained intact.

This helps to explain why checking a smartphone during a restless night can increase feelings of fatigue the next day, but does not have a long-term effect on sleep cycles.

"If these two effects ― acute and long-term light exposure ― were driven through the same pathway, then every minor light exposure would run the risk of completely shifting our body's circadian rhythms," said Prof. Schmidt.

While the study shows that the system of responses to artificial light follows several paths, we still don't know which region of the brain is responsible for handling short-term bursts of light. Because of this, the researcher emphasised the importance of further research to map the differing ways in which the brain reacts to light.

According to the team, this could help people who work in "nocturnal" professions to stay awake through the use of lighting while lessening the health risks linked to sleep deficits (depression, diabetes, cancer).

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