Side-sleeping (sleeping on the left or right side) may protect the brain against Alzheimer's dementia and Parkinson's disease. Surprising, but it's the conclusion of a team of scientists who compared brain scans of different sleep positions.1,2,3
Bonus: Sleeping on your LEFT side may be best of all to enjoy optimum brain health and a strong memory (see below).
Do you normally sleep on your back or your stomach? You might want to reconsider!
During a recent study, scientists discovered that the brain's self-cleaning system, which activates during sleep, performs more efficiently when on your side.
Research by the University of NY at Stony Brook published in The Journal of Neuroscience found side-sleeping to be the best position for clearing harmful toxins from the brain. They found sleeping on the stomach or back makes it more difficult for the brain to perform nightly maintenance.
"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," said Maiken Nedergaard, a primary researcher in the study.
Most people are side sleepers already. But this revelation has profound implications, especially for those in the minority who sleep on their back or stomach.
In all people, toxins linked to memory loss, dementia, and other neurological disorders are produced in the brain during the day. Two such compounds are beta amyloid and tau protein. These are normally and automatically washed from the brain during sleep.
But when allowed to build up, accumulations of beta amyloid and tau protein interfere with brain cell function, causing neurons to die. This can lead to memory loss including Alzheimer's dementia and other neurocognitive problems. Thus, clearing amyloid and protein from the brain during sleep is critical for brain health.
However, it was discovered sleep position affects this nightly brain cleaning. Toxins are eliminated more completely from the brain of individuals who sleep on their side. Because harmful toxins are less likely to build up in their brain, their risk of dementia is reduced.
"The study therefore adds further support to the concept that sleep serves a distinct biological function of sleep and that is to 'clean up' the mess that accumulates while we are awake," said Nedergaard.
Stony Brook researchers used magnetic resonance imaging (MRI) to visualize the "glymphatic system" in the brains of rats while they slept. The glyphatic system, only recently discovered, acts as the brain's "garbage truck."
During sleep this system automatically washes away toxins (including beta amyloid and tau protein) from the cerebral spinal fluid (CSF) that bathes the brain.
"The analysis showed us consistently that glymphatic transport was most efficient in the lateral [side] position when compared to the supine [back] or prone [stomach] positions," said Helene Benveniste, a principal researcher in the study.
Amazingly, then, you can help your brain clean itself each night by sleeping on your side. There's no guarantee you'll avoid dementia or other cognitive problems, but you may improve the odds of keeping your brain healthy.
"Many types of dementia are linked to sleep disturbances, including difficulties in falling asleep," added Nedergaard. "It is increasingly acknowledged that these sleep disturbances may accelerate memory loss in Alzheimer's disease. Our finding brings new insight into this topic by showing it is also important what position you sleep in."
Helping your brain stay clean of toxins is a great reason to sleep on your side. But there are even more reasons side sleeping may be best.
The side-sleeping position is recommended for snorers or those with sleep apnea. That's because the side position keeps the airway more open.5
Keeping the airway clear at night can boost memory formation, because what you experience and learn during the day is consolidated into long-term memory during restful sleep. Snoring and sleep apnea interrupt the nightly memory formation process.
The Stony Brook study on the glymphatic system did not mention whether sleeping on the right or left side is better. From the perspective of the brain's garbage truck, it may not matter.
But for a couple reasons the LEFT side may be best. According to some research, sleeping on the left side can relieve heartburn. (On the other hand, sleeping on the right side can make heartburn worse.)4
Sleeping on the left side can also improve blood circulation. It does this by reducing pressure on the vena cava, the largest vein in the body, which is located on the right side.
This may be especially important for those with circulatory disorders or for pregnant mothers and their unborn children.5,6
It's amazing that something as simple as choosing to sleep on your side can lower the risk of Alzheimer's and Parkinson's disease. Not to mention how it helps with other aspects of health.
I don't know about you, but I'm going to sleep on my side (and mostly on my left side!) from now on.
1. "Could Body Posture During Sleep Affect How Your Brain Clears Waste?" Stony Brook University News August 4, 2015
2. "Sleeping on your side could reduce Alzheimer's and Parkinson's risk, study finds." Science Alert by Peter Dockrill, 13 Aug 2015
3. Nedergaard, Benveniste, et al. "The Effect of Body Posture on Brain Glymphatic Transport," Journal of Neuroscience. 5 August 2015, 35(31): 11034-11044; doi: 10.1523/JNEUROSCI.1625-15.2015
4. "The Claim: Lying on Your Left Side Eases Heartburn." The New York Times, 25 Oct 2010.
5. "How These 3 Sleep Positions Affect Your Gut Health." Healthline.
6. "Sleeping Positions During Pregnancy." American Pregnancy Association.
Last Updated: 06/11/2020