What Sleep Really Does, and Why You Shouldn’t Skimp

Posted on December 16, 2013


A study by Dr. Maiken Nedergaard at the University of Rochester found that “sleep’s critical function is to allow metabolic waste products to be cleared from the brain, which apparently cannot occur during waking hours,”  Medpage Today reports.   If you’re interested, you can read the paper at the NIH website; but essentially, the natural interstitial spaces in a sleeping or anesthetized brain open up by about 60%, allowing for increased circulation of fluids and removal of the by-products of neural activity.  Dr. Nedergaard has dubbed this the “glymphatic system.”

If bathing the brain is the primary function of sleep, this could explain a lot.  For instance, maybe “short sleepers” just have a more efficient glymphatic system and thus, require less time to clear out all those by-products.   Then there is the mystery of how ducks, cetaceans, and manatees sleep with only half the brain at a time; this explains perfectly why a completely coma-like state is not necessary (and for some creatures, maladaptive).  While one half of the brain is being cleansed in sleep, the other half can remain awake and watchful for predators, or enable an animal to continue swimming to the surface for air.

But perhaps the most important implication of this study will be in the area of aging and dementia, because one key by-product of waking brain activity is beta-amyloid proteins… yes, those proteins that form the plaques so characteristic of Alzheimer’s disease.  Indeed, the study abstract makes the connection:   “We propose that this MRI approach may provide the basis for a wholly new strategy to evaluate Alzheimer’s disease susceptibility and progression in the live human brain.”

At this point, there is no knowing whether the plaques of Alzheimer’s disease accumulate through a failure of this circulation system; through sleep disorders that disrupt that system; or maybe some kind of over-production of the beta-amyloid proteins.  But it seems like a pretty safe bet that the chronic sleep deprivation so common in today’s fast-paced society  is even more risky than we previously thought.

It has long been recognized that too many of us get too little sleep, and the problem is getting worse.  The NIH chart below shows that for both men and women of all ages, the percentage “usually” getting less than 6 hours of sleep per night has risen between 1985 and 2004.  Consequences of too little sleep have long been recognized, too, and it’s not just a matter of bleary-eyed, grumpy people operating heavy machinery;  it includes “an increased risk of hypertension, diabetes, obesity, depression, heart attack, and stroke,” writes the NIH.  Now, possibly, we can add dementia to that list of serious long-term consequences.

I know from experience that I can go indefinitely on seven hours of sleep per night.  Eight is better, but any less than seven, and my performance starts to degrade.  The fewer hours, the faster the degradation.  It was pretty typical, when rolling out on a military exercise, to get just two or three hours of sleep for the first two or three nights, but I would crash pretty fast after that.

Pilots – for whom sleep deprivation can have immediate and catastrophic consequences – have well-established requirements for sleep and crew rest.  But for some strange reason, that has never been embraced by certain other groups, like medical interns or, well, non-flying military people.   I thanked my lucky stars never to have worked for certain (ignorant) senior officers who viewed the ability to withstand sleep deprivation as the mark of a great officer.  I had much more respect for those who emphasized immediately putting “sleep plans” into effect for optimum unit performance, and you can bet I followed their lead.

The NIH already views chronically insufficient sleep as a public health problem.   That’s not news, but in light of Dr. Nedergaard’s study, we need to elevate public awareness of the fact that sleep is a physiological need, not a matter of choice or willpower or manliness, and certainly not of leadership.