Osteoporosis is a medical condition in which bones are thin and weakened. The first sign of osteoporosis may be when a bone breaks. Risk factors that a person can change include diet, inactivity, smoking, use of alcoholic beverages (beer, wine, whiskey, etc.), hormone levels, and being underweight. Increasing calcium and vitamin D in the diet, exercising, limiting alcohol use, quitting smoking, and certain medications may help prevent osteoporosis.