The inner clock—Blue light sets the human rhythm

Abstract

Visible light synchronizes the human biological clock in the suprachiasmatic nuclei of the hypothalamus to the solar 24‐hour cycle. Short wavelengths, perceived as blue color, are the strongest synchronizing agent for the circadian system that keeps most biological and psychological rhythms internally synchronized. Circadian rhythm is important for optimum function of organisms and circadian sleep–wake disruptions or chronic misalignment often may lead to psychiatric and neurodegenerative illness. The beneficial effect on circadian synchronization, sleep quality, mood, and cognitive performance depends not only on the light spectral composition but also on the timing of exposure and its intensity. Exposure to blue light during the day is important to suppress melatonin secretion, the hormone that is produced by the pineal gland and plays crucial role in circadian rhythm entrainment. While the exposure to blue is important for keeping organism's wellbeing, alertness, and cognitive performance during the day, chronic exposure to low‐intensity blue light directly before bedtime, may have serious implications on sleep quality, circadian phase and cycle durations. This rises inevitably the need for solutions to improve wellbeing, alertness, and cognitive performance in today's modern society where exposure to blue light emitting devices is ever increasing.

The mediation role of sleep quality in the association between the incidence of unhealthy movement behaviors during the COVID-19 quarantine and mental health

“…Furthermore, physical inactivity can be associated with disorders such as sleep apnea, which is associated with lower sleep quality [ 30 ]. Similarly, higher sedentary behavior, especially screen time can be associated with higher exposure to blue light, which can affect mechanisms related to melatonin release, which is detrimental to sleep quality [ 31 ]. In this sense, poorer sleep quality due to the incidence of unhealthy movement behaviors could explain part of the association of the incidence of unhealthy movement behavior and mental health.…”

Dissecting the Response to Blue Light

“…Research has shown that viewing light with significant energy levels in the blue spectrum near the time when we would normally expect to sleep can negatively impact our circadian rhythms by activating a specific type of retinal cells—intrinsically photosensitive retinal ganglion cells (ipRGCs)—that suppress the sleep hormone melatonin. Studies have found that all light has this suppressive effect to some degree, but blue light's wavelength suppresses melatonin to a far greater extent than warmer colors on the visible spectrum 1 …”

Screen Time Duration and Timing: Effects on Obesity, Physical Activity, Dry Eyes, and Learning Ability in Elementary School Children

“…However, light exposure between morning and evening does not affect the phase of the biological clock [17]. In addition, nighttime light exposure suppresses the secretion of melatonin, a sleep-promoting hormone, from the pineal gland [18][19][20]. This can interfere with sleep onset [18][19][20].…”

“…Thus, ST just before bedtime can be problematic. Among the visible light wavelengths, short wavelengths perceived as the color blue can strongly affect the phase delay of the circadian rhythm, along with suppressing melatonin [18][19][20]. Most digital devices emit blue light.…”