Does light therapy help improve sleep?

Sleep is an essential physiological process impacting numerous biological systems. Adequate sleep duration and quality are crucial for optimal brain function, cardiovascular health, cellular repair, and immune function. Conversely, chronic sleep deprivation has been linked to an increased risk of developing various chronic health conditions, including neurodegenerative diseases.

In our fast-paced world, a good night's sleep often feels like a luxury. Blue light from electronic devices, disrupted sleep schedules, and even seasonal changes can cause devastating damage to our natural sleep-wake cycles. 

Light therapy, also known as photobiomodulation, or phototherapy, has emerged as a promising solution for sleep problems or problems caused by a lack of sleep. This blog explores the science behind light therapy and explores its effectiveness in improving sleep, particularly when targeted at the brain.

Sleep as the ultimate detox for your brain

According to a study from 2023 [1], there is recent evidence indicating that sleep has a housekeeping function, involving the disposal of all the metabolic debris and waste products that have accumulated in the brain during the day. This study mentions that “these waste products need to be cleared; otherwise, they accumulate and become toxic. The brain undertakes this housekeeping function largely by using a flow of fluid that sweeps across the spaces between its constituent neural cells, taking all the waste products with it, draining ultimately into the venous system”. 

Researchers also highlight that “this housekeeping function is not, in fact, too far removed from Aristotle’s original idea, all those centuries ago, that sleep serves to help filter, cleanse and refresh the body and brain” [1, 3].

Chronic sleep deprivation and increased disease risk

Science tells us that individuals who have consistent patterns of good quality sleep tend to live longer and suffer less disease later in life (Iliff et al., 2012; Aspelund et al., 2015; Eugene and Masiak, 2015; Jessen et al., 2015; Loveau et al., 2015, 2017; Brodziak et al., 2018; Hablitz et al., 2020; Mestre et al., 2020; Nedergaard and Goldman, 2020; Reddy and van der Werf 2020; Yan et al., 2021).

In the same way, “sleep appears to be a sensitive biomarker that facilitates early detection and effective intervention for Alzheimer's disease” [2]. There is an increased risk of developing a range of serious medical conditions, including cardiovascular disease, hypertension, diabetes, obesity, psychiatric illnesses (e.g., depression), and neurodegenerative diseases (e.g., dementia and Alzheimer’s disease) when sleep deprivation is chronic [1, 3].

The factors that contribute to poor quality sleep are extensive and varied. They may include the following; medications being used, food and water intake, stress levels, and environmental factors. 

Unfortunately, it does not improve the older we get. In particular, those over 60 years generally have reduced periods of slow-wave sleep, resulting in shorter and lighter sleep patterns, interrupted more often with multiple awakenings [1].

How does light therapy work for sleep?

Light plays a surprising role in our sleep patterns. Light therapy influences sleep through two key mechanisms:

• Circadian rhythm regulation: Our brains have a built-in clock called the circadian rhythm, influenced by sunlight exposure. In the morning, sunlight tells our bodies it's time to wake up and be alert. Darkness, on the other hand, triggers the production of melatonin, the sleep hormone, preparing us for sleep. By exposing the eyes to this light, we can send signals to the SCN (suprachiasmatic nucleus), promoting melatonin production or suppression depending on the timing [3].
• Cellular biomodulation: Light therapy can also exert biological effects through its interaction with the tissues inside the skull. This interaction has the potential to initiate cellular reactions within the mitochondria, potentially contributing to improved sleep.

Scientists are now looking even deeper to understand how this light interacts with the brain on a cellular level. This research focuses on a fascinating system called the glymphatic system. Imagine this as a complex network of channels that flushes out waste products and cellular debris from the brain, particularly active during sleep.

 

 

Credits: Moro, C. et al. (2022)

This schematic describes the glymphatic system, the brain's dedicated waste clearance pathway. The diagram contrasts its activity during wakefulness (left) and sleep (right).

• Wakefulness (left): Thinner lines represent reduced activity in astrocytes – the star players of the glymphatic system – and diminished cerebrospinal fluid (CSF) flow. This equates to a less robust waste removal process, akin to a “sanitation crew” with fewer vehicles operating at a slower pace.

• Sleep (right): Thicker lines indicate heightened astrocyte activity and increased CSF flow. This means a more efficient waste clearance process, comparable to a larger, more diligent “sanitation crew” working swiftly.

Thus, the glymphatic system operates at a significantly enhanced capacity during sleep, promoting optimal brain health by effectively removing waste products [5].

In essence, according to science [3], brain light therapy, or transcranial photobiomodulation (tPBM), can: 

• Enhance drainage, allowing for improved waste clearance;
• Increase mitochondrial activity, enhancing the energy production machinery within brain cells, potentially improving their overall health and waste processing abilities;
• Stimulate immune cells to clear amyloid beta (Aβ) plaques, which are hallmark protein buildup in Alzheimer's disease, promoting blood vessel growth, and further aiding waste removal.

References

1. Valverde, A., Hamilton, C., Moro, C., Billeres, M., Magistretti, P., & Mitrofanis, J. (2023). Lights at night: does photobiomodulation improve sleep?. Neural regeneration research, 18(3), 474–477. https://doi.org/10.4103/1673-5374.350191
2. Zhao, X., Du, W., Jiang, J., & Han, Y. (2022). Brain Photobiomodulation Improves Sleep Quality in Subjective Cognitive Decline: A Randomized, Sham-Controlled Study. Journal of Alzheimer's disease : JAD, 87(4), 1581–1589. https://doi.org/10.3233/JAD-215715
3. Semyachkina-Glushkovskaya, O.; Fedosov, I.; Penzel, T.; Li, D.; Yu, T.; Telnova, V.; Kaybeleva, E.; Saranceva, E.; Terskov, A.; Khorovodov, A.; et al. Brain Waste Removal System and Sleep: Photobiomodulation as an Innovative Strategy for Night Therapy of Brain Diseases. Int. J. Mol. Sci. 2023, 24, 3221. https://doi.org/10.3390/ijms24043221
4. Choy, M., & Salbu, R. L. (2011). Jet lag: current and potential therapies. P & T : a peer-reviewed journal for formulary management, 36(4), 221–231.
5. Moro, Cecile & Valverde, Audrey & Dole, Marjorie & Hoh Kam, Jaimie & Hamilton, Catherine & Liebert, Ann & Bicknell, Brian & Benabid, Alim-Louis & Magistretti, Pierre & Mitrofanis, John. (2022). The effect of photobiomodulation on the brain during wakefulness and sleep. Frontiers in Neuroscience. 16. 942536. 10.3389/fnins.2022.942536.