Shining near-infrared light on the head boosts brain's sleep chemical, study finds

"This is welcome news for insomnia patients who reach for sleeping pills every night."

Shining near-infrared light on the head can increase levels of a natural "sleep substance" in the brain and help induce sleep, according to new research.

The Gwangju Institute of Science and Technology (GIST) announced Wednesday that a research team led by professors Kim Tae and Kim Jae-kwan of the Department of Biomedical Science and Engineering had identified how transcranial photobiomodulation (tPBM) using near-infrared light affects the brain's sleep-regulation process.

The team focused on adenosine, a compound that accumulates in the brain the longer a person stays awake, promoting drowsiness and helping trigger sleep onset. It is one of the key substances regulating what is known as "sleep pressure" — the body's drive to sleep.

The researchers hypothesized that near-infrared light stimulates mitochondrial energy metabolism in brain cells, boosting levels of adenosine triphosphate (ATP), the cell's primary energy source, and that adenosine would rise as a byproduct of ATP breakdown.

When near-infrared light was applied to various types of brain cells, ATP levels increased. In mice, irradiating the head with near-infrared light reduced waking time and extended non-rapid eye movement (NREM) sleep.

In the mouse brain particularly, adenosine concentrations rose and delta waves associated with deep sleep increased. These changes persisted for up to three hours after the near-infrared stimulation ended.

The team also conducted a preliminary clinical trial involving 40 adults with insomnia symptoms. Participants were randomly assigned to either a near-infrared stimulation group or a control group and asked to wear a headband device fitted with near-infrared LEDs for up to one hour each night before bed over one week. The stimulation group received near-infrared light at an 850-nanometer wavelength.

The results showed that the near-infrared stimulation group recorded a 26 percent reduction in the Insomnia Severity Index (ISI) and a 29.6 percent drop in the Pittsburgh Sleep Quality Index (PSQI). Lower scores on both measures indicate improvement in insomnia symptoms and overall sleep quality.

However, the improvements observed in this trial were largely reflected in participants' subjective assessments. Objective sleep metrics measured by wrist-worn devices showed no clear difference between the stimulation and control groups. A separate analysis limited to participants who used the device as directed found that time to fall asleep after putting on the headband fell by about 30 percent.

The fact that adenosine increases were not directly measured in the human brain is another area requiring further research. Whether the adenosine rise observed in animals translates equally to sleep improvement in humans has yet to be established.

"Through this preliminary clinical trial, we confirmed the possibility of improving the insomnia symptoms and sleep quality that participants actually feel," Kim Tae said. "We will verify objective sleep-improvement effects and long-term safety with a larger group of participants, and develop this into a non-pharmacological sleep management technology."

The findings were published online in the international journal Molecular Psychiatry.