An even more vital function of sleep for the brain is janitorial. The zillions of chemical reactions that make life possible inevitably create waste products known as metabolites, some highly reactive and damaging.12 Because the power-hungry brain uses one-fifth of the body’s calories, it generates abundant and highly concentrated metabolites. Some of these garbagy molecules such as beta-amyloid clog up neurons.13 Others such as adenosine make us sleepy as they accumulate (and are counteracted by caffeine).14 Getting rid of these waste products, however, is a challenge.
