The Best Sleeping Position for Glymphatic Flow in the Brain

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Other than getting enough sleep, what can we do to improve the glymphatic clearance of waste from our brains? The provision of a running wheel, so mice could voluntarily exercise, has been shown to improve glymphatic clearance in aging mice, which was accompanied by a reduced buildup of amyloid deposits and improved cognition. Sleeping position may also make a difference.

Studies on rats show that their natural sleeping position, curled up on their sides, allows for better glymphatic transport than sleeping on their backs or stomachs. People also tend to spend most of their time sleeping on their side, particularly their right side versus left, compared to their backs or stomachs. This may maximize blood outflow from the brain. When we sleep on our right side, our right internal jugular vein—the main blood vessel in our neck draining blood from the head—is wide open, and our left jugular is partially collapsed, and vice versa. Since most people have a dominant right jugular vein, sleeping on our right side might maximize brain drainage. Does it matter? Well, people with neurodegenerative disease, mostly mild cognitive impairment and Alzheimer’s disease, tend to sleep more on their backs than those with normal cognition. About 72 percent spent at least two hours a night on their backs compared to 37 percent of those with healthier brains, raising “the intriguing possibility that head position during sleep could influence the clearance of neurotoxic proteins from the brain.”

In crib death, sudden infant death syndrome, sleeping position can be a lifesaver, leading to slogans like “back to sleep,” or more morbidly, “face up to wake up.” It’s premature for an adult jingle. (Maybe “on your flank to not draw a blank?”) The characteristic position of poor sleepers is on their back. So, maybe it’s the poor sleeping rather than the position per se that leads to cognitive decline. Or, the causality could be reversed, with dementia deteriorating good sleep habits. Even if sleeping position did matter, it may take a night in a sleep lab to track your movements. It turns out self-reported sleep positions are often false. Should brain benefits to side sleeping ever be established, you can train yourself with so-called “positional therapies” such as the “tennis ball technique,” which involves wearing a shirt to bed backwards, with a ball stuffed in the chest pocket.

The uncertainties don’t end with sleeping position. The glymphatic mechanism itself was rapidly embraced in scientific circles and the popular press; however, it’s been controversial. It wasn’t until 2019 that the first evidence was published that the glymphatic system discovered in rodents even existed in human brains. Even the relationship between sleep and Alzheimer’s disease is perhaps best summed up in a recent neurology review titled “It’s complicated …” Yes, those getting less than seven hours of sleep may have higher rates of dementia, but those getting more than eight are at higher risk too. If anything, population studies show that longer sleep durations (more than eight or nine hours) are more strongly linked to Alzheimer’s disease and dementia in general than sleeping less than five or six hours.

The association between dementia and long sleep duration could be reverse causation, where prodromal changes in the brain years before Alzheimer’s is diagnosed cause prolonged sleep. Long sleep duration may also just be a confounding factor, a marker of some underlying health problem that is the real culprit. For example, oversleeping may be a sign of depression, which itself is an established risk factor for dementia. But there is a plausible biological mechanism for how extended sleep duration could increase dementia risk directly. Longer sleep duration, typically defined as sleeping more than eight hours a night, is associated with signs of systemic inflammation––elevated levels of C-reactive protein and Interleukin 6. And both of those inflammatory markers, in turn, are associated with an increase in dementia risk. So, much more needs to be teased out about the role of the glymphatic system before we make conscious efforts to tweak it.

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Motion graphics by Avo Media

• aging
• Alzheimer’s disease
• animal studies
• brain health
• C-reactive protein
• dementia
• inflammation
• memory
• sleep