- Researchers have shown that exposure to certain types of light before sleep can negatively affect health.
- In the present study, the scientists wanted to see what effect two different types of light might have on a person’s metabolism during sleep and the quality of their sleep.
- The team found that OLED light had less of a negative effect on metabolism during sleep compared with LED light.
In a new study, researchers explored the effects that different types of light exposure during the evening have on a person’s metabolism during sleep.
The research, which appears in the journal Scientific Reports, offers further evidence for the negative effects that blue light exposure in the evening can have on an individual’s health.
Screen light
For people in many countries worldwide, exposure to various types of screens is a routine part of life.
Whether working at a computer during the day, watching television during the evening, communicating with friends and family over video calls, or checking social media on smartphones, screen exposure is ever present.
Almost all screens work by emitting light. Many screens and various other lighting sources involve the use of light-emitting diodes (LEDs). While they require little power, produce little heat, and have a long life, they do produce significant amounts of blue light.
Research has shown that exposure to short-wavelength light — such as blue light — can disrupt a person’s circadian rhythm.
Researchers have also suggested there may be a link between exposure to bright artificial light and weight gain, insulin resistance, obesity, and more general metabolic disorders.
However, organic light-emitting diodes (OLEDs) produce less blue light than LEDs. OLED technology is becoming increasingly popular in the screens of the latest phones, computers, and televisions.
Because OLED produces less blue light than LED, it could be that the negative health effects associated with LED screen exposure are not as significant in OLED displays.
Sleep study
In the present study, the researchers wanted to see whether OLED screens are less disruptive to a person’s
According to Prof. Kumpei Tokuyama, of the International Institute for Integrative Sleep Medicine, University of Tsukuba, Japan, and the study’s senior author, “energy metabolism is an important physiological process that is altered by light exposure.”
“We hypothesized that compared with LEDs, OLED exposure would have a reduced effect on sleep architecture and energy metabolism, similar to that of dim light.”
In the study, the researchers enrolled 10 males who were in good health, did not smoke, did not have any sleep disorders or work shift patterns, and had not crossed time zones while traveling in the previous month.
In the week before the experiment, the participants maintained a regular sleep pattern. They did not consume alcohol or caffeine in the 3 days before the study.
On the day of the experiment, each participant arrived 6 hours before their normal bedtime. The researchers attached various sensors to them and instructed them to enter a metabolic chamber.
The sensors and the chamber allowed the team to measure the participants’ core body temperature, energy expenditure, melatonin levels, and fat oxidation.
Once in the chamber, they were given 30 minutes to adapt to the darkness and were then served dinner.
The participants were then exposed to either LED, OLED, or dimmed LED light for 4 hours until they reached their normal bedtime. During the light exposure, they completed a sleepiness questionnaire every hour.
When they woke up the next morning, the researchers gave them another questionnaire to assess their sleep and how sleepy they felt on waking.
After an hour of being awake, they received breakfast, and the experimenters monitored them for 4 hours from waking in total, with hourly questionnaires assessing how sleepy they felt.
Less energy expenditure
The researchers found marked differences between the metabolisms of the participants exposed to either OLED or LED light.
According to Prof. Tokuyama, “the results confirmed part of our hypothesis. 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.”
The team also noticed a correlation between fat oxidation and the measure of melatonin levels for the participants exposed to OLED light.
For Prof. Tokuyama, “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.”
According to Prof. Tokuyama and his colleagues, the findings are good news for consumers given the increasing prevalence of OLED screens in various technologies.
“Yes, it is good news,” the researchers told Medical News Today. “The effect of light on energy metabolism depends on the light source, and our results lead to the possibility of choosing a light source depending on the situation.”
“However, in the present study, differences in the spectrum power density of the two light sources were small, and the component that caused the difference in energy metabolism remains to be identified — that is, blue light or light other than blue light, the difference in glare between the two light sources, etc.”
As well as identifying the cause of the difference in energy metabolism, researchers should explore several other avenues for future research, said Prof. Tokuyama and his colleagues.
“In addition to evening light exposure that was evaluated in the present study, the effect of light exposure in the morning remains to be evaluated. In the present study, the acute effect of a single bout of light exposure on energy metabolism was examined — the chronic effects of repeated light exposure also need to be evaluated.”
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