Vitamin C is the essential nutrient that supports the immune system and helps maintain healthy skin, eyes, and bones. It is also called ascorbic acid and is required for several important chemical processes in the body.
One of vitamin C’s best-known roles is helping the body make collagen, a structural protein found in skin, bones, cartilage, blood vessels, gums, and connective tissue. It also helps the body absorb non-heme iron from plant foods. Vitamin C contributes to normal immune function, although taking extra supplements does not guarantee that a person will avoid every cold or infection.
Citrus fruits are famous sources, but peppers, broccoli, strawberries, kiwifruit, tomatoes, and potatoes can also provide substantial amounts. Humans cannot manufacture vitamin C, so it must come from food or supplements. Severe deficiency causes scurvy, historically a major problem for sailors whose diets lacked fresh produce. Vitamin D is important for bones and immunity too, but it is not the answer to this question.