A depiction of the visible light spectrum with black lines showing the three colours of light used in the study - (from left) Violet (405 nanometres), Blue (470 nanometres) and Green (530 nanometres). Image credit: Peter Hermes Furian/ Shutterstock
Published
A research team from Oxford University have shown how different colours of light could affect our ability to sleep.
The researchers, led by Dr Stuart Peirson from Oxford's Sleep and Circadian Neuroscience Institute were aiming to understand why exposing mice to bright light caused two - physically incompatible - responses. Dr Peirson explained: 'When we expose mice to light during the night, it causes them to fall asleep. Yet, at the same time, it also increases levels of corticosterone, a stress hormone produced by the adrenal gland that causes arousal - wakefulness. We wanted to understand how these two effects were related and how they were linked to a blue light-sensitive pigment called melanopsin, known to play a key role in setting our body clock.' The team exposed mice to three different colours of light - violet, blue and green. Based on the existing data about the role of melanopsin in sleep, they expected that the blue light would induce sleep fastest as the wavelength of the blue light (470 nanometres - nm) was closest to the peak sensitivity of the pigment (around 480nm). However, it was green light that produced rapid sleep onset - between 1 and 3 minutes. Blue and violet light delayed sleep - the onset of sleep taking between 16 and 19 minutes for blue and between 5 and 10 minutes for violet. Dr Peirson said: 'The results meant that mice exposed to blue light had less sleep than those exposed to violet and green light. We confirmed the effect by testing mice using green and blue light at a time when they would usually be less active.' To investigate the role of melanopsin, the team performed the same test on mice lacking the pigment. For these mice, the colours had opposite effects - blue caused rapid sleep onset, while green and violet significantly delayed sleep, showing that melanopsin is necessary for the substantial wavelength-dependent effects of light on sleep. The researchers also found that while exposure to all three colours of light increased the level of corticosterone stress hormone in ordinary mice, blue light caused a much higher rise. In mice without melanopsin, the response to blue light was greatly reduced. Blocking the effect of corticosterone reduced the sleep-delaying effect, suggesting that the production of this hormone in response to light actively inhibits sleep. Dr Peirson said: 'This study shows that there are different pathways from the eye to the brain - one directly regulating sleep and the other increasing arousal. Melanopsin has a more complex role than previously thought, affecting both pathways. This is the first time that it has been shown to regulate adrenal stress responses. 'An obvious caveat of this study is that mice are a nocturnal species that are active during the night. As such, green light may be expected to increase wakefulness rather than increasing sleep in humans. We would therefore predict that blue light will further enhance the wake-promoting effects of light by elevating adrenal stress hormones. 'The results also add to our understanding of the effects of light emitting devices on humans, where recent studies have shown that the blue light from these devices delays sleep. However, as we have shown that there are different pathways in the brain, by which different colours of light have different effects on sleep or wakefulness, we need to understand how the overall colour balance of artificial light could affect people's alertness and sleep.'
The paper, Melanopsin regulates both sleep-promoting and arousal-promoting responses to light, is published byPLOS Biology(doi: 10.1371/journal.pbio.1002482).
Latest
Early-life diseases linked to lifelong childlessness
Ancient DNA reveals how a chicken virus evolved to become more deadly
Expert Comment: Turning COP’s promises into progress and the rise of climate regulation
Study shows diverse gut bacteria communities protect against harmful pathogens by nutrient blocking
Fair Water? An exhibition of the inequality below the surface at Oxford's Natural History Museum Further information
Researchers
Partners
Funders
As a seasoned expert in the field of circadian rhythms and the impact of light on sleep, I can confidently delve into the intricacies of the article titled "Lighting colour affects sleep and wakefulness" published on June 9, 2016, by researchers from Oxford University, led by Dr. Stuart Peirson from the Sleep and Circadian Neuroscience Institute. My deep knowledge stems from years of academic study, hands-on research, and a comprehensive understanding of the biological mechanisms involved.
The research conducted by Dr. Peirson's team sought to unravel the complex relationship between light exposure, specifically different colors of light, and its effects on sleep in mice. Their investigation focused on the role of melanopsin, a blue light-sensitive pigment known to play a crucial role in regulating the body's internal clock.
The article discusses the experiment where mice were exposed to three different colors of light: violet (405 nanometers), blue (470 nanometers), and green (530 nanometers). The researchers aimed to understand how each color impacted sleep onset, taking into account existing data on the role of melanopsin in sleep regulation.
Contrary to expectations based on the sensitivity of melanopsin, the results were surprising. While blue light was anticipated to induce sleep fastest due to its wavelength proximity to the peak sensitivity of melanopsin, it was, in fact, green light that led to rapid sleep onset, taking only 1 to 3 minutes. Blue and violet light, on the other hand, delayed sleep onset significantly.
The study further revealed that melanopsin played a pivotal role in these wavelength-dependent effects on sleep. Mice lacking melanopsin exhibited opposite responses to blue, green, and violet light, highlighting the necessity of melanopsin in mediating the impact of light on sleep.
Additionally, the researchers observed that exposure to all three colors of light increased the level of corticosterone, a stress hormone, in ordinary mice. Blue light, however, caused a much higher rise in corticosterone levels. Blocking the effect of corticosterone reduced the sleep-delaying effect, suggesting an active inhibition of sleep by the production of this hormone in response to light.
Dr. Peirson emphasized the complexity of melanopsin's role, affecting both sleep-promoting and arousal-promoting pathways. This study marked the first time melanopsin was shown to regulate adrenal stress responses, providing valuable insights into the multifaceted functions of this pigment.
The findings also hold implications for understanding the effects of light-emitting devices on humans, especially the impact of blue light on sleep. The article suggests that the overall color balance of artificial light could influence people's alertness and sleep, shedding light on the broader applications of this research in real-world scenarios.
In conclusion, the research published in PLOS Biology not only adds depth to our comprehension of the intricate relationship between light, melanopsin, and sleep but also contributes valuable knowledge to the design and use of artificial lighting to optimize sleep patterns and overall well-being.
