Lights at night: does photobiomodulation improve sleep?

Abstract

Sleep is a critical part of our daily routine. It impacts every organ and system of our body, from the brain to the heart and from cellular metabolism to immune function. A consistent daily schedule of quality of sleep makes a world of difference to our health and well-being. Despite its importance, so many individuals have trouble sleeping well. Poor quality sleep has such a detrimental impact on many aspects of our lives; it affects our thinking, learning, memory, and movements. Further, and most poignantly, poor quality sleep over time increases the risk of developing a serious medical condition, including neurodegenerative disease. In this review, we focus on a potentially new non-pharmacological treatment that improves the quality of sleep. This treatment, called photobiomodulation, involves the application of very specific wavelengths of light to body tissues. In animal models, these wavelengths, when applied at night, have been reported to stimulate the removal of fluid and toxic waste-products from the brain; that is, they improve the brain's inbuilt house-keeping function. We suggest that transcranial nocturnal photobiomodulation, by improving brain function at night, will help improve the health and well-being of many individuals, by enhancing the quality of their sleep.

Keywords: aquaporin 4; glymphhatic; infrared; non-pharmacological; red; sleep cap; transcranial; wakefulness.

Figure 1

Schematic diagram of the glymphatic system of the brain. (A) Normal: cerebrospinal fluid (CsF) flows into interstitial space (IsS) through the perivascular space and aquaporin 4 (AQP4) molecule on astrocytes. The interstitial fluid (IsF) is then cleared away into the venous system, together with any cellular waste-products (e.g., β-amyloid). This is the so-called glymphatic system. (B) Disease (or poor quality sleep): glymphatic flow and clearance are much reduced and the flow of IsF through IsS becomes turbulent. This leads to the accumulation of waste products in the IsS (e.g., that may lead to β-amyloid plaque formation), leading to distress and dysfunction in the surrounding neurons (eg, that may lead to the development of neurofibrillary tangles). (C) Photobiomodulation-treated: glymphatic flow and clearance are improved/restored and the surrounding neuropathology is reduced. We suggest that photobiomodulation may work to increase the permeability of the aquaporin-4 water channels on the astrocytes, thereby helping to increase the flow of fluid through the brain. Adapted from Louveau et al. (2017) and Brodziak et al. (2018).