August 19, 2015

Sleeping on Your Side May Lower Alzheimer’s Risk

If you sleep like the guy in this picture, you may be lowering your risk of developing dementia.

We’ve heard some interesting things about sleep recently:
  • Poor sleep increases the risk of heart attack and stroke.
  • Poor sleep is linked to an increased risk of dementia.
  • Sleep creates better conditions for the body to remove dangerous waste products from the brain... the same toxic materials – like amyloid beta and tau proteins -- that accumulate and are now considered hallmarks of both Alzheimer’s disease (AD) and Parkinson’s disease (PD).

Now, as reported in The Journal of Neuroscience, there's a new twist on sleep and health: Sleeping on your side might very well reduce your risk of developing Alzheimer’s.

The Glymphatic System
An international team of researchers led by scientists at Stony Brook University in New York investigated the complex brain cleansing system that removes harmful substances that jeopardize the normal functioning of cells and tissue. That purifying “glymphatic system” filters cerebrospinal fluid (CSF) through the brain and exchanges it with interstitial fluid (ISF) to clear away neural waste, like toxic misfolded proteins.

That glymphatic network works in the brain the same way that the lymphatic system functions to flush out harmful waste products from other organs in the body.

Using magnetic imaging, the research team observed that the brain flushing system worked best when the test subjects were sleeping on their sides -- in the lateral position – and not on their backs or on their stomachs.

According to lead investigator and Stony Brook University professor of anesthesiology Helene Benveniste, “The analysis showed us consistently that glymphatic transport was most efficient in the lateral position when compared to the supine or prone positions.” 

It’s Only Mice
Here’s the rub – the same caveat we see over and over again in promising research: these findings were developed from studies on rodents, not humans.

Even though we’ve learned along the way that it’s a giant leap from mice to men, the news that lateral-position sleep might be best for brain health should be good news to most people, since that’s the way most of us sleep.

In a frequently cited study on human sleeping positions, researchers at the UK’s Sleep Assessment and Advisory Service found that 69% of sleepers rest in one of three of these “most beneficial” lateral positions:
  • The fetus (41%)
  • The log (15%)
  • The yearner (13%)

Fetus sleepers curl their legs and arms up. Log sleepers rest on their sides with straight arms and legs like a plank. Yearners place their arms in front of them.

Starfish, Soldier, Freefaller
Not that many people sleep in other “less beneficial” ways, but the names of the positions are amusing:
  • 8% sleep in the soldier position, lying flat on their backs with arms at the sides.
  • 7% are “freefallers,” sleeping on their stomachs.
  • 5% adopt the starfish position, on their backs with arms up near their heads.

There’s a missing 11% of sleepers. It’s hard to say how they might sleep.

The prevalence of side-sleepers – the position that best enables the brain to cleanse itself of toxins -- may be a result of evolutionary biology. Study co-author Maiken Nedergaard said: 
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. 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.

Nedergaard described the link between dementias and sleep disturbances, including trouble simply 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.”

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The news last week from Stony Brook caused a stir on the internet and was picked up by a variety of outlets, including:

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