Are toxins flushed out of the brain during sleep?

Ask the doctor

Q. I’ve heard that toxins are flushed out of the brain during sleep. Is that true?

A. One of the most interesting discoveries in the past decade is that the brain has a "waste management system." Like people, in order to have the energy to do their work, brain cells need to eat (to absorb, primarily, sugar and oxygen). And, as in people, meals lead to wastes that need to be disposed of. The waste management system (called the glymphatic system) is a series of tubes that carry fresh fluid into the brain, mix the fresh fluid with the waste-filled fluid that surrounds the brain cells, and then flush the mix out of the brain and into the blood. This occurs primarily during deep sleep.

There is some evidence that an under-functioning waste management system may play a role in the neurodegeneration that follows traumatic brain injury (as experienced by some football players, for example). It may even play a role in other brain disorders, including Alzheimer’s disease. Since chronic sleep deprivation increases the risk for various brain diseases, it is plausible that it does so by reducing the function of the waste management system.

Why do we sleep? We know it helps to rest the body and to consolidate memories and learning. Perhaps we also need to sleep to flush wastes from our brain.

— Anthony L. Komaroff, M.D.
Editor in Chief, Harvard Health Letter