When you sleep, your brain cleans up—literally. Cerebrospinal fluid, which surrounds brain cells, scoops up toxic proteins that build up when you’re awake—including beta-amyloid deposits that clump together, destroy nerve cells and are strongly linked to Alzheimer’s risk—and safely gets rid of them. Getting too little sleep (such as only five or six hours a night) or poor quality sleep (waking up repeatedly) has been linked with increased levels of beta-amyloid deposits in older adults.

Last year, we told you about an extraordinary discovery by a team at the University of Rochester Medical Center that unlocks how the brain does this marvelous nightly detox. They studied mice, whose brains (we’re sorry to report) are pretty similar to ours. During sleep, it turns out, brain cells temporarily shrink, which makes more room for cerebrospinal fluid to move between them and sweep the toxic stuff out. (See “How Sleep Sweeps Toxins From Your Brain”)

Now, those same researchers have teamed up with others from Stony Brook University in New York and learned that sleep position matters. So how should you sleep to help your brain stay clean and healthy?

GIVING THE SELF-CLEANING BRAIN A BOOST

The process by which the brain uses cerebrospinal fluid to detox is called the glymphatic system. Previous research has shown that it works virtually the same during anesthesia as during natural sleep, so the researchers anesthetized mice and rats. Contrast dye was injected into their brains so MRI images could be used to calculate how efficiently the glymphatic system was working. The results…

  • Supine (lying face up): This was the worst position.
  • Prone (lying face down): Better.
  • Lateral (lying on the side): Best by far. (For this study, the animals were placed on their right sides.)

Why sleep position matters isn’t known, but researchers suspect that even minor shifts in posture change how well fluids travel through the body. For example, even slight pressure on a blood vessel can significantly reduce the amount of blood flow. They suspect something similar is happening in the brain.

It’s only an animal study, so it isn’t definitive. The researchers hope to follow up with studies in humans soon. But the good news is that sleeping on your side is a pretty natural posture for humans (rodents, too, in case you’re curious). It’s a better position if you tend to snore or have knee or shoulder pain, too (see “Change Your Sleep Position to Relieve Pain, Heartburn, Snoring and More”).

So when you sleep, start on your side. If you wake up and are in a different position, remind yourself to get back on your side. If that’s not easy to do, though, don’t lose any sleep over it. Getting enough sleep, and good quality sleep, is the most important thing for your health.

Learn more in Bottom Line’s “Guide to Better Sleep…No Sleeping Pills Needed.”