Blood oranges. View of several blood orange halves. Blood (or red) oranges are a variety of orange (Citrus sinensis) with red flesh. They are a rich source of vitamin C (ascorbic acid). This is needed to build and maintain healthy bones, teeth, gums and blood vessels, and helps some of the body's enzymes to work properly. Unused vitamin C is quickly excreted by the body in urine and regular dietary intakes are needed to prevent ill health. A person typically consumes about 45 milligrams of vitamin C a day. Lack of vitamin C causes the disease scurvy, where small blood vessels leak and teeth fall out.