Ascorbic acid is a substance that can exist in two forms. These forms include D-ascorbic acid and L-ascorbic acid. They are made up of the exact same components but differ slightly in the way they are arranged. The D and L arrangements are known as enantiomers and appear as mirror images of each other. While enantiomers largely have the same chemical properties, they interact with certain molecules differently.
The D-ascorbic acid does not have any significant physiological activity. It is retained by the body to a lesser extent than its L counterpart and the majority of the administered dose is excreted through urine. It is also metabolized to carbon dioxide but also to a lesser extent than L-ascorbic acid. Both versions of ascorbic acid have antioxidant activity. Antioxidants prevent the formation of free radicals which damage the body's cells. Another similarity is that the body cannot synthesize either form.
L-ascorbic acid, on the other hand, is commonly known as vitamin C. This vitamin is vital to the normal function, growth and repair of tissues. It is particularly important in collagen production. Collagen is the most abundant protein found in mammals and is mainly found in connective tissue. It gives form to the body and offers support to the organs. Vitamin C is required as a cofactor by the enzymes that participate in the synthesis of collagen. So while D-ascorbic acid is not physiologically important, we could not survive without vitamin C. Since vitamin C cannot be synthesized by the body, it is necessary to obtain an adequate daily intake through your diet.