Sleep is one of our most essential, but under-appreciated, human needs. It may seem like a mystery, but scientists have been studying it for decades and understand a lot about how the brain, body and mind work together during sleep to make us feel rested and healthy.

During sleep, our bodies are at work to heal and grow. We get a chance to process our emotions, improve our memory and learn new information. Sleep can also help boost our immune system, making us less likely to catch a cold or other infections, and more likely to respond well to vaccines.

Our sleep patterns are influenced by genetics, environment and lifestyle. Some people have a harder time falling asleep than others, and some struggle to stay asleep. While there is no definitive answer as to why this happens, we do know that getting more sleep and improving your sleep habits can help you feel better physically, mentally and emotionally.

While most experts agree that we need sleep for health, many of us don’t get enough. Studies show that adults need between 7 and 9 hours of sleep each night for optimum health. Insufficient sleep is associated with a number of short- and long-term health effects, including lowered concentration and performance, weight gain, high blood pressure, heart disease, depression, poor mood and decreased energy. Those who suffer from certain chronic conditions, such as diabetes and heart disease, are at an even greater risk of not getting enough sleep.

Sleep is a complex state of reduced mental and physical activity during which consciousness is altered, sensory activity is inhibited, and muscles are at rest. During sleep, the heart and blood vessels work to heal from any damage they have sustained during the day. In addition, the body’s metabolism slows down, lowering blood sugar levels and reducing the risk of developing diabetes.

The most obvious signs that you are sleeping include the slowing of your breathing, a reduction in movement and a loss of muscle tone. There is no universal sleep stage; it varies from person to person, but most people spend about two-thirds of their time in non-rapid eye movement (NREM) sleep and the other third in rapid eye movement (REM) sleep. During NREM sleep, the brain waves are similar to those during wakefulness, and in REM sleep, the eyes move rapidly behind closed lids.

Research suggests that sleep is necessary for the consolidation of memories, learning and emotional responses. Sufficient sleep is also important for mental health, and a lack of it can increase the risk of suicide or the intensity of existing mental illnesses, such as anxiety and depression.

Though we know that sleep is crucial for good health, millions of people don’t get enough. It is important to prioritize sleep just as we do a balanced diet, exercise and social interaction. It’s also important to recognize any potential sleep disorders and seek treatment if needed. Especially for people who are underserved, such as Black and Latino populations and those in lower socioeconomic statuses, whose health risks from not getting adequate sleep are often under-recognized or undertreated.