The Science behind Helight Sleep

Summary of scientific publications 2000-2019 relating to the effects of light on humans and circadian rhythms: metabolism and CNS with a focus on sleep.

In 2002, Berson and Hattar published 2 complementary papers which describe the presence and the functioning of intrinscally photoreceptive retinal ganglion cells: ipRGCs which contain the photoreceptor pigment called melanopsin: thus explaining how light can influence the circadian rhythms.

A few years later, Hattar (2006) and Benarroch (2011) demonstrated that the numerous connections of these cells with different areas of the brain are at the origin of the influence of light outside the visual system. As Hattar had already described in 2003, Lucas also confirmed in 2012 that the retinal cells related to sight (cones and rods) also contribute to this influence by stimulating the glial cells.

Over the past decade, many research teams have studied the influence of light on various biological processes (regulation of body mass, general metabolism and homeostasis), but also on well-being (depressive syndrome). Preclinical studies have described the consequences of too much light or, conversely, of total light deprivation. On the occasion of this work, and by testing the influence of the spectral composition of light, a team noticed in 2013 that hamsters exposed to longer wavelength (red) photons during the night were less sensitive to stimulated depression, and exhibited less alteration in neuronal structure than hamsters exposed to blue light.

At the same time, numerous clinical studies have also been carried out and published, in particular on the duration and quality of sleep following a first publication by Wallace-Guy in 2002. The processes by which light influences sleep have thus often been associated with changes in hormonal expression. In 2010, Figueiro and Rea published a very interesting study on the influence of blue light and red light on circadian variations in the production of cortisol, alpha-amylase and melatonin, demonstrating a differential effect of these 2 types of light.

The negative influence of exposure to light rich in spectral components of short wavelength in the evening has been demonstrated in particular by many authors including Chang (2015) and Chinoy (2018): longer sleep sequence, reduction in melatonin production, delay of the circadian clock, impaired vigilance the next day …

Other authors have focused on the influence of the environment on the quality of sleep, looking at light exposure at work or during the entire sleep phase. These publications have led to a more general interest in the health effects of exposure to different artificial light sources. A satellite radiometric study was published in 2017, showing that human exposure to artificial light sources is increasing in intensity and area every year. Yet, the evidence continues to accumulate regarding the negative influence on health and well-being of exposure to artificial light at night, but further investigation needs to be carried out to better understand and characterize these results, in particular by refining the dosimetric aspect.

A recent article (Wisse 2018) suggests that exposure to red light may suppress the negative consequences of previous exposure to blue light.

In addition, Figueiro and his team showed in 2019 that exposure to red light during sleep significantly reduced sleep inertia upon waking.

Dr. Olivier Caselles

PhD. – Medical Physicist – IUTC – Oncopole Toulouse



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