About 20 percent of American adults — 50.2 million people — live with chronic pain, saying they experience it most days or every day, according to a report from the Centers for Disease Control and Prevention on the health status of U.S. adults. The most common types are back pain (reported by about 41 percent of those with chronic pain) and hip, knee or foot pain (about 44 percent), according to an analysis of the CDC data by Harvard researchers and published in the journal Pain. Other frequent sources of chronic pain include an old injury, infection, headaches, nerve damage and such diseases as cancer, arthritis and diabetes. Chronic pain is known to affect people’s physical and mental health as well as their social and work lives. For instance, the report found that people with chronic pain say it makes them unable to work about 10 days a year, compared with about three missed workdays for those who do not have chronic pain. As a result, the researchers attribute roughly $80 billion a year in lost wages to chronic pain as well as a nearly $300 billion loss per year in productivity, based on the monetary value of goods and services not produced because of chronic pain. The analysis also found that, to manage their pain, people most often turn to physical therapy or massage, each tried by about 9 million of those with chronic pain. Other options may include medication, acupuncture or surgery, but health experts said that chronic pain is not always curable, although treatments may help.