"Know one short night cuts immune defense 70% Walker describes an experiment in which participants had their sleep restricted to just four hours for a single night — not eliminated entirely, just reduced — and then had their immune activity measured. The result was not a modest dip: there was "a 70 drop in natural killer cell activity," the immune cells responsible for identifying and destroying cancerous tumor masses. Walker connects this directly to research showing significant links between short sleep and cancers of the bowel, prostate, and breast, and notes that the World Health Organization has classified nighttime shift work as "a probable carcinogen" because of the sleep disruption it causes. Anyone who trims sleep to a few hours to gain productive time is trading long-term immune resilience for short-term output. Source: Matt Walker, TED, Sleep is your superpower"