According to research by Elizabeth Klerman, an associate professor of medicine at Harvard Medical School and Brigham and Women’s Hospital, most adults should be getting 8.5 to 9 hours of sleep each night. Learn about her study and about the benefits of a good night’s sleep. Plus, HMS Associate Professor of Medicine Julia Wang explores what causes the immune system to attack healthy cells and tissues by mistake. Photo by Jojomarie/stock.xchng.