Expert says side-sleeping may help clear brain toxins and protect memory

A brain health expert has said sleeping on one’s side — either left or right — may help clear toxic proteins from the brain and could reduce the risk of memory decline, a claim that highlights a growing interest in how sleep posture affects long-term cognition.

Lev Fomchenkov, chief executive of online supplement seller Cosmic Nootropic, told the Daily Mail that side-sleeping allows cerebrospinal fluid to circulate more effectively through brain tissue via the glymphatic system, the pathway that clears metabolic waste during sleep. "When you sleep on your side, gravity actually helps the cerebrospinal fluid circulate more effectively through your brain tissue," he said, adding that better clearance could reduce accumulation of proteins linked to Alzheimer's disease.

The glymphatic system is most active during sleep, when the space between brain cells expands and cerebrospinal fluid can wash away waste. Studies have shown that interstitial space can increase substantially during sleep — by roughly 60 percent in some animal studies — facilitating this clearance. Two proteins commonly associated with Alzheimer’s disease, beta-amyloid and tau, can accumulate in brain tissue over years; researchers believe their progressive build-up is implicated in the development of the condition.

Fomchenkov said back-sleeping may compress certain brain regions and stomach-sleeping can disrupt spinal alignment, each potentially impeding glymphatic function. He recommended gradual changes for people who normally sleep on their back or stomach, advising the use of a small pillow between the knees to preserve hip and spine alignment and placing a pillow behind the back to prevent rolling while adapting to a new position.

The claim that side-sleeping is superior for brain clearance complements other guidance on sleep posture that focuses on comfort and breathing. The Mayo Clinic generally recommends side sleeping to reduce pressure on joints and to promote spinal alignment. Mayo Clinic sleep specialist Dr. Lois Krahn has warned that sleeping on the back can worsen obstructive sleep apnea in some people because "your tongue and jaw can fall down and crowd your airway." Clinicians also commonly advise against stomach-sleeping because it can strain the neck and compromise spinal alignment.

Experts caution, however, that the relationship between sleep position and long-term memory decline is not settled science. While studies in animals and imaging research in humans suggest that sleep and the glymphatic system play roles in clearing metabolic byproducts, the extent to which changing sleep position alters lifetime risk of dementia has not been established definitively. The topic divides researchers and clinicians, and much of the public discussion reflects preliminary findings rather than consensus guidelines.

Alzheimer’s disease is the most common cause of dementia, which describes a progressive decline in cognitive function. The Alzheimer’s Society estimates there are about 982,000 people living with dementia in the United Kingdom, with projections that figure could rise to 1.4 million by 2040. Beta-amyloid plaques and tau tangles develop over years or decades and are only part of a complex set of biological processes associated with neurodegeneration.

In practical terms, experts say sleep quality and duration remain central to brain health. "Most people think about sleep in terms of duration, i.e., getting those recommended eight hours," Fomchenkov said, "however, position may also play an important role in brain health." He also recommended choosing a pillow that fills the gap between shoulder and neck to maintain neutral head position and selecting a mattress that offers contouring support to avoid pressure points, as discomfort can disrupt restorative sleep.

Clinicians and sleep scientists urge people to consider individual health needs when changing sleep habits. For individuals with obstructive sleep apnea, back sleeping can exacerbate airway obstruction; for people with chronic neck or back pain, mattress and pillow choice and overall spinal alignment are important determinants of comfort and sleep quality. Any attempt to alter sleep posture should balance potential benefits against these other health considerations.

Research into the glymphatic system and its role in human brain health is active and evolving. While side-sleeping is a low-risk behavioural change that may improve comfort and reduce some sleep-related breathing problems, claims about its capacity to prevent dementia should be treated as preliminary until supported by longitudinal human studies that directly link sleep posture to long-term cognitive outcomes.