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Sleeping in the lateral, or side position, as compared to sleeping on one’s back or stomach, may more effectively remove brain waste, and could reduce the chances of developing Alzheimer’s, Parkinson’s and other neurological diseases, according to researchers at Stony Brook University.
They discovered this in experiments with rodents by using dynamic contrast magnetic resonance imaging (MRI) to image the brain’s glymphatic pathway, a complex system that clears wastes and other harmful chemical solutes from the brain. They also used kinetic modeling to quantify the CSF-ISF exchange rates in anesthetized rodents’ brains in lateral, prone, and supine positions.
Most Popular Position: “It is interesting that the lateral sleep position is already the most popular in human and most animals — even in the wild — and it appears that we have adapted the lateral sleep position to most efficiently clear our brain of the metabolic waste products that built up while we are awake,” says Dr Maiken Nedergaard, a co-author at the University of Rochester.
“The study therefore adds further support to the concept that sleep subserves a distinct biological function of sleep and that is to ‘clean up’ the mess that accumulates while we are awake. Many types of dementia are linked to sleep disturbances, including difficulties in falling asleep. It is increasingly acknowledged that these sleep disturbances may accelerate memory loss in Alzheimer’s disease.”
Cerebrospinal fluid (CSF) filters through the brain and exchanges with interstitial fluid (ISF) to clear waste in the glymphatic pathway, similar to the way the body’s lymphatic system clears waste from organs. The glymphatic pathway is most efficient during sleep. Brain waste includes amyloid β (amyloid) and tau proteins, chemicals that negatively affect brain processes if they build up.
Abstract: The glymphatic pathway expedites clearance of waste, including soluble amyloidβ (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.
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.
