The importance of sleep and brain health – the glymphatic system explained

Every night while you sleep, the brain runs a system and goes through a type of maintenance cycle, which is as important as anything you do while you’re awake. This system is called the ‘glymphatic system’. Discovered only 14 years ago by Danish neuroscientist, Dr. Maiken Nedergaard and her team Rochester, New York, the glymphatic system is considered to be one of the biggest breakthroughs in science and has changed the way we think about sleep, ageing and cognitive function throughout life.

Once thought of as a luxury, sleep is now acknowledged to be a necessity. Every hour you’re awake, thinking, moving and processing the world, your brain cells are hard at work. As a by-product of this hard work, metabolic waste is produced in the form of  proteins that accumulate between the brain’s cells throughout the day. This waste is only cleared when we’re asleep, but if it isn’t cleared and continues to accumulate, then over time it can impact memory and everyday cognitive function.

As Professor Phil Haydon explains, ‘when the brain is exposed to repeated stress or in a similar manner, sleep is interrupted or insufficient, the protective processes serving our brain health are suddenly compromised. Sleep is when the brain is cleared of toxic waste through the glymphatic system, while memories and the day’s events are consolidated. That’s why sleep and reducing stress is so important – as over time sustained imbalance and chronic neuroinflammation can interfere with neuroplasticity which is needed to help maintain brain health in later life.’

The glymphatic system, responsible for clearing this waste, uses cerebrospinal fluid – the clear liquid that cushions the spinal cord and brain. It uses this as a cleaning fluid, for when we sleep, our brain cells shrink slightly allowing this fluid to flow freely between them. As this process begins, levels of noradrenaline, a chemical messenger tied to alertness and stress, quickly drop, and this signals back to the glymphatic system that it’s time to switch into high gear. The cerebrospinal fluid makes its way along the channels that run beside blood vessels, washes through brain tissue and carries out the waste products. It sweeps them out of the brain and into the blood stream, ready to be processed and removed.

What is important during this clear-up process is the proteins that are removed: amyloid-beta and tau. These proteins are the hallmarks of Alzheimer’s disease. They form as sticky plaques and tangled fibres that have the capability to damage and eventually kill brain cells over time. We all produce amyloid-beta and tau proteins as a normal by-product of everyday brain activity, but clearing these waste products out before they have time to accumulate is the secret to brain health longevity.

When we don’t get the sleep we need, even after a single night, studies have found that these proteins accumulate significantly. A recent randomised study found that a full night of normal sleep led to a greater clearance of these proteins than a night of sleep deprivation did, in the very same people. This shows that there isn’t an ongoing process of waste clearance in the background. The glymphatic system depends solely on sleep happening consistently, night after night, for as soon as you wake up, this process slows abruptly. This is why consistent, uninterrupted sleep matters a great deal. It’s the only real window the brain gets to do this clean-up process effectively and efficiently.

As the years go by, there are important age related changes which affect the glymphatic system. Our blood pressure tends to rise with age, we become less active, we put on weight and there are changes in our circulatory system. We now know that it is possible to counteract these biological trends with simple lifestyle changes, and in doing so, we can slow down the decline of the glymphatic system. One of the biggest changes as we age is in our sleep patterns. We fall asleep less easily, our sleep is more shallow and we wake up more easily. We still need 7-8 hours of sleep per 24h cycle, and in later life this can be managed by afternoon naps limited to no more than one hour. Not being able to adapt and modify our ways as we age can greatly impair the glymphatic system, so managing age related changes is key.

This isn’t meant to be alarming. Poor sleep happens to all of us, and the odd sleepless night won’t undo good brain health. Chronic, disrupted or insufficient sleep on a regular basis however, will have an impact on cognitive function. Brain fog and poor concentration are often experienced, as well as slower reaction times and poor memory recall. This happens because the hippocampus hasn’t had its usual window of being able to consolidate memories from the day gone.

Research is now beginning to view sleep as a modifiable pathway helping to reduce the risk of dementia in later life. Here are four ways to help you get the sleep you need each night, protecting your brain health for years to come.

Four ways to get a good night’s sleep:

1. Keep a consistent sleep window. Going to bed and waking up at roughly the same time every day, weekends included, helps to regulate your body’s internal clock and circadian rhythm so deep sleep can come more easily.
2. Wind down before bed. Switch the screens off and dim the lights at least an hour before bed. This helps noradrenaline levels drop naturally, which is one of the signals for the glyphatic system to begin its night time work. 
3. Keep your bedroom cool, dark and quiet. A cool room between 16–19°C supports the natural drop in body temperature that helps trigger and sustain deep sleep. A dark, quiet environment reduces the chance of waking mid-cycle, setting the stage for a sleepful night.
4. Sleep on your side, preferably the right. Recent research has shown that the rate of glymphatic drainage slows down dramatically if we sleep in the prone position (lying on our back). On either side, glymphatic drainage is much more efficient than prone (face up) or supine (face down).

For more information on sleep, visit our sleep pillar.