4. Sleep refreshes your immune system.
The idea that sleep resets your brain doesn’t just apply to the brain, but also to the immune system, which fights infections by day but reorganizes itself and replaces dead cells by night. This is because the entire body—down to each teeny, tiny cell—operates on a 24-hour clock, says Gianluigi Mazzoccoli, MD, director of the Scientific Institute and Regional General Hospital (Casa Sollievo della Sofferenza) in Italy.
“Day and night are characterized by completely different spectra of physiological functions,” Dr. Mazzoccoli says. “And the immune system is absolutely directed by these distinctions of periods.”