Sleep plays a key role in keeping the immune system strong. During sleep, the body releases important immune signaling molecules and increases the production of protective cells and antibodies. Without enough quality sleep, these defenses weaken—making us more likely to get sick and reducing how well vaccines work. Sleep also helps regulate inflammation, including in the gut, where it influences both digestion and the balance of gut bacteria. When sleep is disrupted, inflammatory molecules in the blood rise, increasing the risk for a range of health problems.