Daily exposure to blue wavelength light each morning has been linked to enabling people to sleep better by ‘re-entraining’ their circadian rhythm.

And researchers at the University of Arizona have now demonstrated that it may be particularly useful in people recovering from mild traumatic brain injury (mTBI).

In a randomised clinical trial, adults with mTBI used a cube-like device that shone bright blue light at participants for 30 minutes early each morning for six weeks. Control groups were exposed to bright amber light.

Lead author William D. “Scott” Killgore, psychiatry professor in the university’s College of Medicine – Tucson, says: “Blue light suppresses brain production of a chemical called melatonin. You don’t want melatonin in the morning because it makes you drowsy and prepares the brain to sleep.

“When you are exposed to blue light in the morning, it shifts your brain’s biological clock so that in the evening, your melatonin will kick in earlier and help you to fall asleep and stay asleep.”

People get the most restorative sleep when it aligns with their natural circadian rhythm of melatonin – the body’s sleep-wake cycle associated with night and day.

“The circadian rhythm is one of the most powerful influences on human behavior,” Killgore says. “Humans evolved on a planet for millions of years with a 24-hour light/dark cycle, and that’s deeply engrained in all our cells.

“If we can get you sleeping regularly, at the same time each day, that’s much better because the body and the brain can more effectively coordinate all these repair processes.”

As a result of the blue light treatment, participants fell asleep and woke an average of one hour earlier than before the trial and were less sleepy during the day.

Participants improved their speed and efficiency in brain processing and showed an increase in volume in the pulvinar nucleus, an area of the brain responsible for visual attention.

Neural connections and communication flow between the pulvinar nucleus and other parts of the brain that drive alertness and cognition were also strengthened.

“We think we’re facilitating brain healing by promoting better sleep and circadian alignment, and as these systems heal, these brain areas are communicating with each other more effectively. That could be what’s translating into improvements in cognition and less daytime sleepiness,” Killgore says.

Computers, smartphones and TV screens often give blue light a bad reputation.

But according to Killgore, “when it comes to light, timing is critical. Light is not necessarily good or bad in-and-of-itself. Like caffeine, it all comes down to when you use it. It can be terrible for your sleep if you’re consuming coffee at 10 o’clock at night, but it may be great for your alertness if you have it in the morning.”

He and his team plan to continue their research to see if blue light improves sleep quality and how light therapy might affect emotional and psychiatric disorders.

Killgore believes that most people, whether injured or healthy, could benefit from correctly timed morning blue light exposure, a theory he hopes to prove for certain in future studies.