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Researchers find blue light alters metabolism during sleep

Researchers exposed 10 men to LED, OLED, or dim light for four hours before sleeping in a metabolic chamber. During sleep, the researchers examined energy expenditure, core body temperature, fat oxidation, and melatonin levels. The participants hadn’t traveled or worked in a shift in a long time.

Excessive exposure to light during the night has been shown to be harmful to human health. However, Japanese researchers have discovered a new form of light that has fewer physiological effects during sleep.

Researchers from the University of Tsukuba compared the effects of light-emitting diodes (LEDs), which have been widely adopted for their energy-saving properties, with organic light-emitting diodes (OLEDs) on physical processes that occur during sleep in a study published in June 2021 in Scientific Reports.

Polychromatic white LEDs emit a lot of blue light, which has been connected to a lot of bad things, including metabolic issues. OLEDs, on the other hand, produce a polychromatic white light with less blue light. However, the effects of LED and OLED exposure at night have not been compared in terms of changes in energy metabolism during sleep, which is something the University of Tsukuba researchers wanted to investigate.

Professor Kumpei Tokuyama, the study’s principal author, said, “Energy metabolism is a key physiological mechanism that is changed by light exposure. We hypothesized that OLED exposure, when compared to LEDs, would have a lower influence on sleep architecture and energy metabolism, similar to dim light.”

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Spectral power distribution of LED, OLED, and dim lights expressed in irradiance. (Credit: Nature)

The researchers tested this idea by exposing 10 male participants to LED, OLED, or dim light for four hours before sleeping in a metabolic chamber. During sleep, the researchers examined energy expenditure, core body temperature, fat oxidation, and 6-sulfatoxymelatonin, a melatonin level measure. The participants hadn’t traveled or worked in a shift in a long time.

“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.”

Furthermore, after exposure to OLED, fat oxidation during sleep was positively linked with 6-sulfatoxymelatonin levels, implying that the influence of melatonin activity on energy metabolism differs depending on the kind of light.

“Thus, light exposure at night is related to fat oxidation and body temperature during sleep. Our findings suggest that specific types of light exposure may influence weight gain, along with other physiological changes,” says Professor Tokuyama.

Before sleeping, many vocations and activities require exposure to artificial light. New knowledge on the impact of various types of light on body processes may make it easier to choose alternate light sources to reduce the detrimental effects of nighttime light exposure. Furthermore, these findings add to our understanding of how light affects energy metabolism during sleep.


The study was published on June 11th, 2021 in Scientific Reports.

Abstract. Light exposure at night has various implications for human health, but little is known about its effects on energy metabolism during subsequent sleep. We investigated the effects of polychromatic white light using conventional light-emitting diodes (LED) and an alternative light source, organic light-emitting diodes (OLED), producing reduced spectral content in the short wavelength of blue light (455 nm). Ten male participants were exposed to either LED, OLED (1000 lx), or dim (< 10 lx) light for 4 h before sleep in a metabolic chamber. Following OLED exposure, energy expenditure and core body temperature during sleep were significantly decreased (p < 0.001). Fat oxidation during sleep was significantly reduced (p = 0.001) after the exposure to LED compared with OLED. Following exposure to OLED, fat oxidation positively correlated with the 6-sulfatoxymelatonin levels, suggesting that the role of melatonin in lipolysis differs depending on the light. These findings advance our knowledge regarding the role of light in energy metabolism during sleep and provide a potential alternative to mitigate the negative consequences of light exposure at night.

Discussion. The present study is one of the first to show that evening light exposure affects metabolism by selectively utilizing substrates during sleep and the subsequent morning after waking. The contrasting metabolic outcomes observed in the LED and OLED conditions may indicate differences in the spectral composition of light in which the short wavelength of blue light negatively affects energy metabolism by increasing the RQ and decreasing fat oxidation during sleep and after waking. Because the spectral composition and melanopic lux between LED and OLED did not differ greatly, it is important to note that characteristics of light, apart from wavelength, such as the glare, luminance, and frequency of fluctuation49, may play an additional role in human physiology. Nevertheless, these findings suggest that OLED may be a viable alternative source of light at night.

Ishihara, A., Park, I., Suzuki, Y. et al. Metabolic responses to polychromatic LED and OLED light at night. Sci Rep 11, 12402 (2021). https://doi.org/10.1038/s41598-021-91828-6

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