Lying on the side is the most common sleep position for humans. And fascinating new research from Stony Brook University may explain why: A side-sleeping position seems to improve waste clearance from the brain, which could prevent Alzheimer’s disease and neurodegenerative diseases.
A few years ago, researchers at the University of Rochester discovered that the brain has its own cleansing system, known as the glymphatic system. Similar to the lymphatic system in the body, the glymphatic system flushes waste products out of the brain.
The finding is significant because some of these waste products, specifically amyloid beta and tau proteins, are believed to contribute to Alzheimer’s disease and other neurodegenerative diseases.
Knowing that the glymphatic system is most active during sleep, scientists at Stony Brook University wanted to see if sleep position affected how well the system worked.
The study, recently published in the Journal of Neuroscience, used dynamic contrast magnetic resonance imaging (MRI) to observe the glymphatic pathway of rodents under anesthesia in three different positions: on their sides (lateral position), backs (supine position), and bellies (prone position).
The results: “The rodents who were in the lateral position cleared amyloid beta about 25 percent better than when in the prone or supine position,” lead study author Dr Helene Benveniste tells Yahoo Health.
Clearing waste products efficiently ensures that they don’t build up in the brain. “When amyloid beta builds up it can form aggregated plaques, which are very difficult for the brain to get rid of,” Benveniste says. These plaques are a telltale characteristic of Alzheimer’s disease, according to the Alzheimer’s Association.
How the Brain Clears Out Waste
The glymphatic system consists of channels that run alongside all of the vessels in the brain, Benveniste explains. Cerebrospinal fluid circulates in these channels throughout the brain, even the deepest parts of it, to flush out waste products. The waste products end up in the body’s lymph system, which clears them out via the blood.
The glymphatic system is mostly inactive during the day, explains Robert Rosenberg, DO, author of Sleep Soundly Every Night, Feel Fantastic Every Day, who was not involved in the new study. But during sleep, the size of the canals increases by about 60 percent, allowing the cerebrospinal fluid to course through the body at a much more rapid rate, he says.
The discovery of the glymphatic system is “really Earth-shaking … because it really gives us an idea of why we sleep,” Rosenberg says. “It seems that one of the reasons why we sleep is to clean the brain out of toxins that build up during the day.”
A side-sleeping position may improve this process, Benveniste explains, because it encourages the flow of cerebrospinal fluid throughout all of the brain’s nooks and crannies. “Probably the reason the head up or back positions are not ideal is because the fluid exits prematurely and does not enter the brain, but instead flows [through] other places, including the spinal cord,” she says.
There are other good reasons to sleep on your side, too, notes sleep expert W. Christopher Winter, who was not involved in the new study. “The lateral position is also best for snoring and sleep apnea,” he says.
“I usually try to get people to sleep on their sides. While it can make shoulders and hips hurt in some and may not be best for reducing the pull of gravity on breasts, it is probably the healthiest position.”
Deep Sleep Crucial for Brain Function
While the new findings are interesting, Rosenberg says he’s not ready yet to tell people to sleep on their sides for the purpose of preventing Alzheimer’s. “The fact that lying on a lateral position improved it in rodents is great, and it may mean something, but I wouldn’t be telling people to all lie on their sides because of that at this point,” says Rosenberg. “The most important take-home message is for people to get a good night’s sleep” because it gets the glymphatic system going.
“If you’re only sleeping four or five hours a night, that may be why you’re having trouble concentrating and focusing,” he adds. “It also may be why we think there’s a relationship between people who for years go with less than six hours of sleep who seem to have a higher incidence of Alzheimer’s.”
To encourage deep sleep, Rosenberg recommends:
1. Avoiding caffeine before bedtime, which tends to wake people up during the night.
2. Keeping a set sleep-wake schedule (that is, going to bed and getting up at the same time every day) to train the body’s rhythms.
3. Limiting alcohol before bedtime, since it takes people out of deep sleep.
4. Turning off blue lights, like those emitted from phones and laptops, before bedtime; they discourage deep sleep.