Wash your brain while you sleep

In previous newsletters, we’ve discussed the importance of sleep for optimal health and performance. In addition to decreasing the risk of numerous chronic diseases, sleep is when we restore energy levels, repair tissues, and recover from a hard workout. Sleep also helps to regulate appetite, improves mood and mental clarity, and increases immune function.

This week we’re going to focus on another incredibly important function of sleep: removing waste. For all metabolic processes that occur in your body, there is an associated waste. The lymphatic system works with the circulatory system to clear this waste. Lymphatic vessels collect waste from your cells and dump it into the blood to be disposed of to keep your body clean and healthy.

Your brain is made up of around 100 billion neurons! These neurons (or nerve cells) send and receive messages so that you can think, concentrate, and learn throughout the day. This means that your brain is very metabolically active and just like every other part of your body, needs a way to dispose of the waste that accumulates during the day so that it’s healthy and clean. This is done through the glymphatic system.

For a long time, researchers didn’t know how the brain cleared itself of waste. However in 2013, a group of researchers at the University of Rochester discovered that it all comes down to sleep. Looking at mice, the researchers discovered that when we sleep, our brain cells shrink by about 60%, allowing for cerebrospinal fluid to come in and pick up all the waste products that have accumulated throughout the day. This “cerebrospinal fluid wash” is critical for repairing any damage, preparing the brain for the next day, and disposing of waste products, including β-amyloid, which is associated with Alzheimer’s disease.

Figure from Xie et al. 2013. The researchers used in vivo two-photon imaging and fluorescent tracers to compare the influx of cerebrospinal fluid (CSF) in the brains of awake versus sleeping mice. When awake, there is a suppression of CSF. During sleep, there is a large influx of CSF into the interstitial space that allows for metabolic waste to be cleared by the glymphatic system.

We now know how important sleep is for the clearance of waste products. This means when you wake up in the morning and feel refreshed, it’s because you’ve actually washed your brain while you sleep! So make sure you’re prioritizing sleep and maintaining a consistent sleep schedule so you can keep your brain squeaky clean.

What are we finding in the research?

In 2013, Lulu Xie and colleagues at the University of Rochester, were the first to highlight the importance of sleep for clearing out waste products in the brain. Looking at sleep-wake states in rats, these researchers discovered that the extracellular space in the brain increases by about 60% during slow wave sleep (deep sleep). This increase in space allows for the glymphatic system to clear the brain of metabolic waste during the night. The researchers describe sleep as “taking out the trash”.

Learn more about the study here.