New research suggests that sleeping on your side could help cut the chances of developing some neurological disorders, including Alzheimer's and Parkinson's. Compared to sleeping on one's back or stomach, sleeping on one's side appears to allow the brain to more efficiently remove waste chemicals that may contribute to the development of such conditions.

The research team, led by Helene Benveniste, MD, PHD, a Professor in the Departments of Anesthesiology and Radiology at Stony Brook University School of Medicine, used dynamic contrast magnetic resonance imaging (MRI) to view the glymphatic pathway in rodent brains. This is the system in mammals responsible for clearing wastes and other harmful chemical solutes from the brain by way of cerebrospinal fluid (CSF) filtering through the brain and exchanging with interstitial fluid (ISF).

It is during sleep that the glymphatic pathway is most efficient at removing brain waste, including amyloid β and tau proteins, whose build up in the brain is associated with Alzheimer's and Parkinson's. The researchers ascertained the efficiency of this system in the brains of anesthetized rodents in the side, down and up sleeping positions by viewing the CSF-ISF exchange rates via MRI.

"The analysis showed us consistently that glymphatic transport was most efficient in the lateral (side) position when compared to the supine (up) or prone (down) positions," said Dr. Benveniste. "Because of this finding, we propose that the body posture and sleep quality should be considered when standardizing future diagnostic imaging procedures to assess CSF-ISF transport in humans and therefore the assessment of the clearance of damaging brain proteins that may contribute to or cause brain diseases."

Colleagues at the University of Rochester validated the MRI data and assessed the influence of body posture in clearing amyloid from the brains using fluorescence microscopy and radioactive tracers.

"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. Nedergaard, PHD, from 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. Our finding brings new insight into this topic by showing it is also important what position you sleep in."

Although the researchers expect the human glymphatic pathway will also clear brain waste most efficiently when a person sleeps on their side, tests on humans are still required to confirm this.

The team's paper appears in the Journal of Neuroscience.