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Review
. 2019 Dec;12(12):e201900102.
doi: 10.1002/jbio.201900102. Epub 2019 Sep 2.

The inner clock-Blue light sets the human rhythm

Siegfried Wahl  1   2 , Moritz Engelhardt  1 , Patrick Schaupp  2 , Christian Lappe  2 , Iliya V Ivanov  1   2
Affiliations
Review

The inner clock-Blue light sets the human rhythm

Siegfried Wahl et al. J Biophotonics. 2019 Dec.

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.

Keywords: blue light; circadian rhythm; melanopsin; melatonin; visible light.

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Conflict of interest statement

S.W., M.E., and I.V.I. are researchers at the University of Tuebingen; S.W., P.S., C.L., and I.V.I. are employed by Carl Zeiss Vision International GmbH, manufacturing spectacle lenses and sunglasses. There is no conflict of interest regarding this study.

Figures

Figure 1
Figure 1
Cross sectional view of the retinal system. Light traverses the system from the left, cones and rods transmit visual information via the bipolar cells, amacrine cells, and ganglion cells to the optic nerve. The sparse subset of intrinsic photosensitive retinal ganglion cells can induce signals themselves, due to their possession of a separate photopigment, melanopsin
Figure 2
Figure 2
Signal transduction of circadian information. A melanopsin induced signal from the ipRGCs is transmitted via the retino‐hypothalamic tract (blue) to the hypothalamic pacemaker neurons in the suprachiasmatic nucleus (green), the human “master clock”. The circadian information is transmitted further downstream via the paraventricular nucleus (yellow), intermediolateral cell column in the vertebral gray matter, superior cervical ganglion (brown) to the pineal gland (purple), which is responsible for melatonin secretion
Figure 3
Figure 3
Physiological melatonin levels of a 24 hour day. Declining light exposure in the evening results in an increased melatonin production by the pineal gland with peak levels in the middle of the night almost 10‐fold higher than regular day levels (adapted from 33)
Figure 4
Figure 4
Irradiance of the blue light hazard function. The Blue light hazard function according to ISO 8980 represents the relative spectral sensitivity of the human eye to blue light hazards, based on the effectiveness of radiation to induce photoreversal of bleaching. The emission spectrum of an ordinary smartphone screen on maximum brightness shows a distinct overlap in the potentially harmful blue peak area, and melanopsin sensitivity, but also image‐forming related S‐cone and rod absorbance spectrum. Normalized absorbance spectra are depicted according to Bowmaker and Dartnall, 1980 19
Figure 5
Figure 5
Light emitting device usage during the day. Usage has been approximated by the share of device dependent web page traffic. It has been reported, that blue light exposure up to 4 hours prior to sleep can affect the melatonin levels at night and subjective sleep quality. Figure modified according to 79
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References

    1. Woodland Hastings J., Sweeney B. M., Biol. Bull. 1958, 115(3), 440.
    1. Provencio I., Jiang G., Willem J., Hayes W. P., Rollag M. D., Proc. Natl. Acad. Sci. 1998, 95(1), 340. - PMC - PubMed
    1. Gooley J. J., Lu J., Chou T. C., Scammell T. E., Saper C. B., Nat. Neurosci. 2001, 4(12), 1165. - PubMed
    1. Berson D. M., Dunn F. A., Takao M., Science 2002, 295(5557), 1070. - PubMed
    1. Berson D. M., Trends Neurosci. 2003, 26(6), 314. - PubMed

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