The Glymphatic System – Crucial for Brain Health – Only Works During Sleep

How do brain cells get rid of their waste products? The answer was only discovered in 2014, and solved a decades old problem. It only happens during sleep. Several other vital processes only occur during sleep as well.glumphatic-green

The Glymphatic System is new. Scoop your doctor. It was discovered in 2014.

Cells are efficient and recycle everything they can, but there is some waste product. For most of the body, this is dumped into the lymph system where it makes it way to the liver for final disposal. The lymph system is found everywhere in the body with one exception, the brain. But the brain is a very active organ, uses a lot of energy, and generates a fair amount of waste.

For over a century, it was assumed that detritus from active neurons was somehow cleared by the cerebral spinal fluid. However, quite a few things didn’t really add up. Apparently, there is not enough contact with the neurons to accomplish this. So the mystery remained.

The research that finally sorted this out will probably be worth a Nobel prize. It is about two years old and quite amazing. It seems that all the blood vessels in the brain are surrounded by a second wall. So it’s a tube within a tube. The inner tube performs its normal blood circulation function, but the space between the inner and outer wall carries the cellular junk away. The discoverers named this the glymphatic system, a combination of glia, the helper cells in the brain that build and maintain the system, and the lymph system. The discoverer, Nedergaard, injected dye into a mouse and got the amazing picture above.

OK, nice to know the brain can drain, but what has this to do with sleep?  It turns out this drainage system only works while you sleep. No sleep—no drainage. Poor sleep—poor drainage. So for this reason, sound sleep is more crucial for proper brain function that previously imagined. During the day the trash piles up. It’s emptied at night. This process, we should say its disruption, is linked to all forms of dementia but particularly Alzheimer’s disease.

glumphatic-sleepBody Repaired While You Sleep

Sleep turns out to be a rather busy time. With so much activity going on all night, it’s amazing we aren’t exhausted when we wake up and would be but for that wonderful melatonin which basically knocks us completely out, resting us, and which peaks about the same time as cortisol starts to rise. Too little melatonin and we have a restless disrupted sleep and not enough garbage gets taken out via the glymphatic system.

Soon after the onset of sleep, Growth Hormone (GH) shoots way up, maybe 10 fold over daytime levels, and stays high for six hours. One can immediately conclude that any benefit from GH occurs almost entirely during sleep. Insulin and glucose rise also, though not as dramatically. GH stimulates production of IGF-1 which gives any damaged cells needing to repair, the green light to proceed. In the absence of IGF-1, non-urgent repairs, like sore muscles, will be postponed. You thought you built muscles in the gym, but it actually happens in your sleep. (Repair of a wound is a different matter entirely. It is locally controlled and obviously immediate.)

Testosterone, which functions as a body wide ‘OK to rebuild’ signal also increases during sleep, as does thyroxin, another growth stimulator.

Some sleeping pills suppress the growth hormone secretion, an undesirable side effect.

Around 4AM, cortisol starts to rise, peaking at 8AM or so. The reason for this is unknown. Maybe it’s to jar you awake.

Good sound sleep is crucial for good health.

  5 comments for “The Glymphatic System – Crucial for Brain Health – Only Works During Sleep

  1. paul
    April 26, 2015 at 4:36 pm

    I would like to find out about your system

  2. Norma
    April 26, 2015 at 7:52 pm

    Sleep gets us physically out of the way for many things,and I’m sure this has to be one of the reasons.

  3. donna
    August 16, 2015 at 5:39 am

    I am a med student and would like to know more

  4. Jim
    September 17, 2015 at 1:22 pm

    Is there any evidence that would support the integration of naps and if napping can help with sleep deficits and improve health?

    • September 21, 2015 at 10:33 am

      A little vexed in the literature, Jim. The clearest supportable line goes like this: 30 minutes or less before 3 PM in the day. The problem with longer, later naps is they can disrupt the diurnal cycle of ‘sleep’ hormones. Dr. Mike

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