Technically speaking, ascorbic acid as the antioxidant is the synthetic version of L-ascorbic acid, or vitamin C, and is usually found in supplement form. Vitamin C is an essential nutrient obtained from the diet. It is found mainly in fruits and vegetables, especially citrus fruits. There is some debate as to whether ascorbic acid has the same effect on the body as natural vitamin C, but according to Oxford University, they are considered chemically the same.

Ascorbic acid, or vitamin C, serves a variety of functions in humans. It is used in the production of collagen, and it aids in protein metabolism. It is necessary for wound healing, helps strengthen the immune system, and assists in the absorption of iron obtained from plant-based foods. Vitamin C is also considered a natural antioxidant, meaning that it helps protect the body from free radical damage. Lack of ascorbic acid in the diet can cause fatigue, muscle weakness and suppressed immune function. In rare cases, severe deficiency results in scurvy, a disease characterized by extreme fatigue, shortness of breath, joint pain, sunken eyes, swollen gums, vision problems and slow-healing wounds.

According to the National Institutes of Health, adults need at least 75 to 90 mg of vitamin C per day. The needs of pregnant and nursing women are slightly higher, at 80 to 120 mg daily. The range for infants and children is 15 mg to 45 mg per day. These are only minimum requirements designed to prevent deficiency. Natural sources of vitamin C include citrus fruits, strawberries, bell peppers, sweet potatoes, tomatoes, broccoli, peas and spinach. However, the foods with the highest concentration of vitamin C are red bell peppers at 95 mg per serving, and orange juice at 93 mg per serving. Grapefruit juice and kiwis are also high in vitamin C.

More is not necessarily better. Large doses of ascorbic acid can cause nausea, gas, bloating and diarrhea. Excessive vitamin C intake also increases urinary excretion, and may lead to kidney or urinary tract disorders. Loss of fluid can also lead to vitamin loss, especially water-soluble vitamins such as the B vitamins. The National Institutes of Health further warns that taking high doses of supplemental vitamin C may cause chromosomal and DNA damage, increasing the risk of developing cancer. Talk to your healthcare provider before trying either ascorbic acid or natural vitamin C supplements, such as ester-C.