Although the findings are yet to be tested in humans, a study suggests sleeping posture affects how well the brain clears away waste products. Accumulation of waste products in the brain is a hallmark of neurodegenerative diseases such as Alzheimer's and Parkinson's.

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The study suggests sleeping on one's side helps the brain clear waste products more effectively.

In The Journal of Neuroscience, researchers say their findings suggest sleeping in the lateral, or side position - as compared with sleeping on one's back or stomach - appears to help the brain remove waste products more effectively and may thus reduce the chance of developing neurodegenerative diseases.

Increasingly, research is showing that sleep is important for brain health. Studies suggest that the brain is better at removing waste products when asleep than awake. And researchers are also discovering that poor sleep is linked to an increased risk of dementia.

So, if the brain removes waste better during sleep, then does body posture during sleep make any difference?

This was the question the team, led by Helene Benveniste, a professor of anesthesiology at Stony Brook University, NY, set out to investigate.

Sleep position affects efficiency of cerebrospinal fluid filtering

For their study, the researchers focused on a complex system in the brain that clears away harmful substances that threaten to disrupt the normal function of cells and tissue.

The system - called the glymphatic pathway - filters cerebrospinal fluid (CSF) through the brain and exchanges it with interstitial fluid (ISF) to clear waste. The process resembles the lymphatic system that clears waste from organs in other parts of the body.

The glymphatic pathway is most efficient during sleep. It clears away potentially toxic chemicals from the brain - including amyloid beta and tau proteins. Build-up of these proteins is a known hallmark of Alzheimer's disease.

The team used dynamic contrast magnetic resonance imaging (MRI) and computer modeling to measure CSF-ISF exchange in the brains of anesthetized rodents in three positions: lateral (lying on side), prone (lying on stomach) and supine (lying on back).

The analysis showed consistently that the glymphatic system was most efficient when the rodents were lying on their side than when they lay on their stomachs or on their backs.

Prof. Benveniste concludes:

"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."

Sleeping on one's side common among humans and most animals

The researchers note with interest that sleeping on one's side is the most popular position in humans and most animals, even in the wild.

They suggest their findings lend further support to the idea that sleep serves an important biological function - to "clean up" the mess that builds up when we are awake.

Co-author Dr. Maiken Nedergaard, who leads a specialist lab for studying brain function at the University of Rochester, NY, says:

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

Prof. Benveniste cautions that while they believe the same happens in our brains, it needs to be confirmed with further research using MRI or other imaging methods in human subjects.

Meanwhile, Medical News Today recently learned that poor sleep may raise the risk of heart attack and stroke. This was the conclusion of a study - led by the Russian Academy of Medical Sciences in Novosibirsk - that followed over 650 men for 14 years and found poor sleep was linked to double the risk of a heart attack and up to four times the risk of stroke.