In studies of humans and other animals, they have discovered that sleep plays a critical role in immune function, metabolism, memory, learning, and other vital functions . The features in this section explore these discoveries and describe specific ways in which we all benefit from sleep. Too much sleep — as well as not enough sleep — raises the risk of chronic diseases , such as coronary heart disease, diabetes, anxiety and obesity in adults age 45 and older. Sleeping too much puts you at greater risk of coronary heart disease, stroke and diabetes than sleeping too little. A review of 15 studies found that people who don't get enough sleep are at far greater risk of heart disease or stroke than those who sleep 7–8 hours per night ( 15 ). Sleeping less than 7–8 hours per night is linked to an increased risk of heart disease and stroke . Sleep helps control our metabolism and weight , promotes stable moods, helps prevent cardiovascular diseases, boosts our immune system/...