Side sleeping helps clean brain through glymphatic transport
Sleep is a physiological imperative because metabolic waste and other harmful substances, including amyloid beta, are flushed from the brain as the neurons contract to allow enhanced drainage through the glymphatic system (as described in Stunning discovery links brain and immune system). Now scientists who published the groundbreaking study entitled Sleep Drives Metabolite Clearance from the Adult Brain have reported their investigation into the effect of sleep posture on brain clearance of wastes in a paper published in The Journal of Neuroscience. The authors state:
"The glymphatic pathway expedites clearance of waste, including soluble amyloid beta (Aβ) from the brain. Transport through this pathway is controlled by the brain's arousal level because, during sleep or anesthesia, the brain's interstitial space volume expands (compared with wakefulness), resulting in faster waste removal. Humans, as well as animals, exhibit different body postures during sleep, which may also affect waste removal. Therefore, not only the level of consciousness, but also body posture, might affect CSF-interstitial fluid (ISF) exchange efficiency."
They quantified CSF (cerebrospinal fluid) and ISF exchange rates with dynamic-contrast-enhanced MRI in their subjects' brains in supine, prone and lateral lying postures, adding fluorescence microscopy and radioactive tracers to measure clearance of Aβ. The lateral (side-lying) posture was clearly the best for 'flushing' the brain:
"The analysis showed that glymphatic transport was most efficient in the lateral position compared with the supine or prone positions. In the prone position...transport was characterized by "retention" of the tracer, slower clearance, and more CSF efflux along larger caliber cervical vessels."
Glymphatic transport during sleep clears brain Aβ
The brain 'takes out the trash' during sleep, and the lateral/side-lying posture appears to be superior in facilitating brain 'drainage'.
"The major finding of our study was that waste, including Aβ, removal was most efficient in the lateral position...We propose that the most popular sleep posture (lateral) has evolved to optimize waste removal during sleep and that posture must be considered in diagnostic imaging procedures developed in the future to assess CSF-ISF transport in humans."
Clinical Note
The rhythmic expansion and contraction of the cranium associated with CSF hydraulics helps drive transport through the glymphatic system. This highlights the clinical value of treatment methods that relieve restrictions in cranial motion such as BioCranial Therapy.