Press Release2020.7.13｜International Institute for Integrative Sleep Medicine (WPI-IIIS)

Turn Off the Blue Light!
Researchers from University of Tsukuba in collaboration with Yamagata
University scientists find that exposure to light with less blue before sleep isbetter for energy metabolism
Tsukuba, Japan—Extended exposure to light during nighttime can havenegative consequences for human health. But now, researchers from Japan
have identified a new type of light with reduced consequences forphysiological changes during sleep.
In a study published in June 2021 in Scientific Reports, researchers fromUniversity of Tsukuba compared the effects of light-emitting diodes (LEDs),
which have been widely adopted for their energy-saving properties, withorganic light-emitting diodes (OLEDs) on physical processes that occur
during sleep.
Polychromatic white LEDs emit a large amount of blue light, which has been
linked with many negative health effects, including metabolic health. In
contrast, OLEDs emit polychromatic white light that contains less blue light.
However, the impact of LED and OLED exposure at night has not been
compared in terms of changes in energy metabolism during sleep,
something the researchers at University of Tsukuba aimed to address.
"Energy metabolism is an important physiological process that is altered bylight exposure," says senior author of the study Professor Kumpei Tokuyama.
"We hypothesized that compared with LEDs, OLED exposure would have a
reduced effect on sleep architecture and energy metabolism, similar to thatof dim light."
To test this hypothesis, the researchers exposed 10 male participants to LED,
OLED, or dim light for 4 hours before they slept in a metabolic chamber. The

researchers then measured energy expenditure, core body temperature, fatoxidation, and 6-sulfatoxymelatonin—which is a measure of melatoninlevels—during sleep. The participants had not recently traveled orparticipated in shift work.
"The results confirmed part of our hypothesis," explains Professor
Tokuyama. "Although no effect on sleep architecture was observed, energy
expenditure and core body temperature during sleep were significantly
decreased after OLED exposure. Furthermore, fat oxidation during sleep
was significantly lower after exposure to LED compared with OLED."
In addition, fat oxidation during sleep was positively correlated with 6sulfatoxymelatonin levels following exposure to OLED, suggesting that theeffect of melatonin activity on energy metabolism varies depending on thetype of light exposure.
"Thus, light exposure at night is related to fat oxidation and bodytemperature during sleep. Our findings suggest that specific types of light
exposure may influence weight gain, along with other physiologicalchanges," says Professor Tokuyama.
Many occupations and activities involve exposure to artificial light before
sleep. New information about the effects of different kinds of light on
physical processes may facilitate the selection of alternative light sources tomitigate the negative consequences of light exposure at night. Furthermore,these findings advance our knowledge regarding the role of light in energy
metabolism during sleep.
The work was supported financially by the Japan Society for the Promotionof Science (KAKENHI grant no. JP 20H04120) and the Japan Science andTechnology Agency's Centre for Innovation (grant no. JPMJCE1312). The
authors declare no competing interests.
About IIIS
IIIS was launched by the Ministry of Education, Culture, Sports, Science andTechnology of Japan with the aim of building globally visible researchcenters with high research standards and excellent research environments
to accommodate globally prominent researchers. IIIS is the world’s premierinstitute aiming to elucidate the fundamental principles of sleep/wakebiology, develop new strategies to diagnose, prevent, and treat sleep
disorders, and contribute to promote human health through research
activities. The research was funded by the Japan Society for the Promotionof Science and the Japan Science and Technology Agency.

Bibliographic information
Ishihara A, Park I, Suzuki Y, Yajima K, Cui H, Yanagisawa M, Sano T, Kido J, Tokuyama K.
(2021) Metabolic responses to polychromatic LED and OLED light at night.
Scientific Reports
doi: 10.1038/s41598-021-91828-6
Media Contact
Alliance and Communication Unit, International Institute for Integrative Sleep Medicine(WPI-IIIS), University of Tsukuba, Japan
E-mail: wpi-iiis-alliance@ml.cc.tsukuba.ac.jp