The position you sleep in could have a significant effect on your neurological health, a new study has found. Researchers say that sleeping on your side, in what's known as the lateral position, may help to remove waste products in the brain that contribute to neurological diseases such as Alzheimer's and Parkinson's.
An international team of scientists led by researchers at Stony Brook University in the US used MRI scans to image the brains of rats, and found that the animals' glymphatic pathways – the system that removes waste chemicals from the brain – was aided in its task when the rodents slept on their side.
The researchers' technique let them observe how cerebrospinal fluid filters through the brain and passes waste to the interstitial fluid between cells in order to clear it from the brain. Such waste includes amyloid and tau proteins, which can impair the brain's functioning if they're allowed to build up.
"The analysis showed us consistently that glymphatic transport was most efficient in the lateral position when compared to the supine or prone positions," said principal investigator, Helene Benveniste, in a statement.
The findings, published in The Journal of Neuroscience, will come as good news to most sleepers, since the lateral position is the most common sleeping position people use.
Back in X year, one of the most widely cited studies on human sleeping positions was conducted by researchers at the Sleep Assessment and Advisory Service in the UK. Its survey found that 69 percent of sleepers rest in one of three lateral positions - the foetus, log, or yearner positions.
Foetus sleepers (41 percent) curl their legs and arms up, log sleepers (15 percent) rest on their side with straight arms and legs like a plank, while yearners (X percent) place their arms in front of them.
Comparatively, very few people sleep on their tummy or back. Eight percent adopt the soldier position - lying flat on their back with arms at the sides - while starfish sleepers (5 percent) lie on their back with their arms up near their heads. Just 7 percent of people sleep on their stomachs, in what's called the freefaller position.
While the glymphatic pathways testing has so far only been conducted on rodents, the researchers speculate that the same benefits of lateral sleeping would apply to humans, although they say further studies are needed to confirm this.
"It is interesting that the lateral sleep position is already the most popular in human and most animals – even in the wild – and 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 co-author of the research. "The study therefore adds further support to the concept that sleep subserves a distinct biological function of sleep and that is to 'clean up' the mess that accumulates while we are awake."
"Many types of dementia are linked to sleep disturbances, including difficulties in falling asleep," she added. "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."