According to the USDA, a medium-sized orange contains approximately 69.7 milligrams of vitamin C, while a small orange contains 51.1 milligrams, and a larger one 97.9 milligrams. The Mayo Clinic states that the recommended amount of vitamin C intake for an adult is between 65 and 90 milligrams a day, so eating one medium orange a day will provide the daily requirement for the average adult.
Vitamin C is a water soluble vitamin that helps the body absorb iron and supports normal growth and development. The highest amount of vitamin C an adult should consume in a day is 2,000 milligrams. Any amount of vitamin C that is not needed by the body will be passed out through the urine.
According to the Mayo Clinic, some health risks are involved with taking too much vitamin C. These include nausea, diarrhea, headaches and kidney stones. To decrease the chances of consuming excessive amounts of the vitamin, it is recommended that individuals get their vitamin C through proper diet rather than supplements.