Literature is full of odes sung in praise of sleep; poets have likened it to a gift from the heavens. Read up any healthy lifestyle checklist; getting your nightly quota of beauty sleep always features somewhere in the list.

Sleeping pills are one of the most commonly purchased over-the-counter medicines. Nobody doubts the benefit of sleep and scientists have proven that sleep is restorative. The body heals itself when we sleep. Some research studies have also identified another fundamental purpose of sleep — to eliminate harmful neurotoxins from the brain that would otherwise go on to trigger Alzheimer’s disease, dementia, Parkinson’s disease, and a host of other debilitating neurodegenerative conditions.

However, a recent study has added one more intriguing detail to the above findings. According to this study, sleeping on your side eliminates waste products from the brain more effectively. The clues are in the glymphatic pathways of our brains.

The role of the glymphatic pathway

Neural cells are extremely sensitive to their environments. Therefore, toxins produced in the brain have to be eliminated quickly to prevent cell damage.

The brain is not served by the conventional lymphatic system that filters out toxic waste products from the other parts of the body. Instead, the brain has a mechanism whereby cerebrospinal fluid (CSF) enters the brain, circulates around it, and exchanges with interstitial fluid (ISF). This process filters out the waste products from the brain while providing nutrients to the neural cells, regulated by the glymphatic pathways. And according to scientists, the efficiency of this system depends on how we sleep!

When we are awake, the normal metabolic workings of the central nervous system produce harmful toxins as by-products that accumulate in the ISF. These include the beta-amyloid peptide and tau proteins. It is believed that an abnormal accumulation of these substances triggers the symptoms of Alzheimer’s disease.

Lack of sleep is also known to bring on brain impairment and a decline in cognitive functionalities that manifest as slower reaction times, difficulty learning and remembering, and an increased incidence of seizures. Severe cases of insomnia have also been known to cause dementia and even death.

The importance of the glymphatic pathway was also highlighted in a recent study on subjects who had suffered some form of traumatic brain injury (TBI). During this study, it was discovered that the functionality of the glymphatic pathway was reduced by up to 60 percent in subjects with TBI.

Imaging studies also showed that these patients had an abnormal accumulation of tau protein in their brains. Now it is known that TBI is a risk factor for the early onset of dementia and Alzheimer’s disease. So, scientists suggest that the impairment of the glymphatic pathway and the resultant neural cell damage can increase the chances of a person developing neurodegenerative disorders, slipping into a coma, or even dying.

The rate at which waste matter clears from the brain is a critical consideration in human beings. Some toxic solutes like peptides produced in the brain have large areas and thus take more time to filter out of the brain than smaller molecules. So the efficiency of the glymphatic system is also determined by the amount of bulk flow it promotes. The greater the flow, the faster the larger molecules will be eliminated from the brain.

The rate of clearance of the waste products from the brain can provide critical insights to determine the appearance and calculate the progression of neural diseases. These can help detect the early warning signs of debilitating diseases like Alzheimer’s disease and allow a person take steps to stall its progress.

The way the glymphatic pathway works when we sleep

Scientists had long been intrigued to know why sleep is conserved across all natural species. They were certain that sleep promotes a vital biological function. They now know.

The concentration of metabolic by-products like amyloid-beta and tau proteins in the ISF is higher when an individual is awake than when he is asleep. It indicates that these substances are produced more during waking hours than during sleep. The studies also discovered that these by-products were cleared faster from the brain when the subject was asleep than when he was awake.

A recent study reveals that the position in which one is sleeping also affects the rate of clearance of brain waste matter. An experiment was carried out on laboratory mice in three sleep positions — when they were lateral, prone, and supine. During the tests, it was discovered that the waste cleared from the brains (that is, the glymphatic pathway functioned more efficiently) of these animals faster when they were in a lateral position.

In this context, it is interesting to note that the lateral position is the most common sleeping position in human beings and many animals. So it seems that Mother Nature knew what she was doing to keep her creations healthy.

The implications of the new findings

Scientists should further investigate this startling find, in order to figure out why the efficacy of the glymphatic system improves in a particular sleeping position. Such knowledge will not only help them find out more about the workings of the waste clearance system of the brain but may also provide valuable insights into why neural diseases develop and how they progress. These findings should also help them research and develop pharmacological methods to improve the functionality of the glymphatic pathways to help those with compromised systems stall neural decay and improve the quality of their lives.

In the meantime, you may try falling off to sleep while lying on your side, in case that is not your usual sleeping position.

References

Iliff, J., Lee, H., Yu, M., Feng, T., Logan, J., Nedergaard, M., & Benveniste, H. (2013). Brain-wide pathway for waste clearance captured by contrast-enhanced MRI Journal of Clinical Investigation, 123 (3), 1299-1309 DOI: 10.1172/JCI67677

Iliff, J., Chen, M., Plog, B., Zeppenfeld, D., Soltero, M., Yang, L., Singh, I., Deane, R., & Nedergaard, M. (2014). Impairment of Glymphatic Pathway Function Promotes Tau Pathology after Traumatic Brain Injury Journal of Neuroscience, 34 (49), 16180-16193 DOI: 10.1523/JNEUROSCI.3020-14.2014

Kelly, K., Mikell, C., & McKhann, G. (2014). Sleep Tight Neurosurgery, 74 (2) DOI: 10.1227/01.neu.0000442978.07078.e5

Lee, H., Xie, L., Yu, M., Kang, H., Feng, T., Deane, R., Logan, J., Nedergaard, M., & Benveniste, H. (2015). The Effect of Body Posture on Brain Glymphatic Transport Journal of Neuroscience, 35 (31), 11034-11044 DOI: 10.1523/JNEUROSCI.1625-15.2015

Strittmatter, W. (2013). Bathing the brain Journal of Clinical Investigation, 123 (3), 1013-1015 DOI: 10.1172/JCI68241

Xie, L., Kang, H., Xu, Q., Chen, M., Liao, Y., Thiyagarajan, M., O’Donnell, J., Christensen, D., Nicholson, C., Iliff, J., Takano, T., Deane, R., & Nedergaard, M. (2013). Sleep Drives Metabolite Clearance from the Adult Brain Science, 342 (6156), 373-377 DOI: 10.1126/science.1241224

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