When you don’t get enough sleep for just a short time, your body’s immune cells become more active in a way that triggers inflammation, which might raise your risk for diseases like heart disease, arthritis, and diabetes.

When you only get 4 hours of sleep, your body’s immune cells get activated in a way that causes inflammation, and this happens even if your stress hormone levels don’t change.

Skipping sleep from midnight to 3 a.m. one night can spike a key inflammation signal in women’s blood cells by about 30%, but not in men—meaning sleep loss might affect women’s bodies differently at a cellular level.

Staying awake from 11 PM to 3 AM doesn't change the numbers of different types of immune cells in the blood of healthy middle-aged people.

Skipping a few hours of sleep doesn't raise your stress hormone (cortisol) in the morning, even though it still turns on your body's inflammation system—so your inflammation isn't caused by that stress hormone.

When people don’t get enough sleep, women’s bodies show a stronger immune reaction than men’s — specifically, a key inflammation signal called NF-κB turns on in women but stays quiet in men.