Vitamin C, also known as ascorbic acid, is one of the many micronutrients consumed through diet that is essential to life. Vitamin C is an organic (carbon-based) compound, with a chemical structure expressed as C6H8O6.
Vitamin C is a water-soluble compound, which permits it to be absorbed into the body directly through the small intestine. Unlike the fat-soluble vitamins A, D, E, and K, vitamin C is not stored for indefinite periods in the body's tissues. Vitamin C is stored for temporary periods within the liver, and any excess amounts are excreted as urine through the renal system.
Vitamin C performs two critical functions within the body, both of which are of the utmost importance to athletic performance. First, it is a facilitator in the absorption of iron by the body, the mineral necessary to the transport of oxygen within the bloodstream. Second, vitamin C is an important component in the ability of the body to manufacture collagen, the protein with elastic properties that is employed in the formation and maintenance of all bones, teeth, and connective tissues. Vitamin C also assists in the maintenance of the capillaries, the smallest vessels of the cardiovascular system.
Vitamin C is present in large quantities in many varieties of citrus fruits, green vegetables, and potatoes. Many of these foods are excellent sources of the vitamin, a standard often defined as one serving of the food has at least 10% of the recommended daily allowance (RDA) of the vitamin. The generally accepted international minimum standard for vitamin C intake is 90 mg per day for an adult male and 75 mg per day for an adult female, with nursing mothers requiring between 100 mg and 120 mg per day. A good dietary source for vitamin C or any other micro-nutrient is also one where the caloric content is appropriate; the benefits of excellent vitamin C content in a particular food must be weighed against the number of calories otherwise contained in it.
Vitamin C is often described as an antioxidant, as it inhibits the actions of oxygen on cells. Contact with oxygen, called oxidation, degrades human cells and tissues, much in the same fashion that bare metal will rust if exposed to the air and elements. The oxidation process creates a multitude of compounds known as free radicals, electrically charged and unstable compounds, which are possessed of one or more electrons that are not paired within the molecule. These compounds are so named because they will seek out otherwise chemically stable molecules from which to remove electrons necessary to bring their own structure into balance. The removal of an electron from a previously stable nearby molecule creates a chain reaction that causes cellular damage, whereby that previously stable compound will itself seek to obtain a replacement. Vitamin C acts as an antioxidant through the provision of one of its own available charged particles, giving up an electron to stop cycle of cell damage. Vitamin C also protects the fat-soluble vitamins A and E, and accompanying fatty acids, from oxidation as they are transported throughout the body.
A diet lacking vitamin C may cause various negative effects including oxidative stress (exposure of the cells to the adverse effects of oxidation). Those whose bodies are subjected to greater than normal oxidative stress for various reasons, including strenuous exercise, tobacco and alcohol consumption, dialysis, viral illness and fever, or other stressful conditions, require correspondingly greater quantities of vitamin C. Severe vitamin C deficiency may lead to scurvy, a debilitating condition, characterized by a lack of energy, tooth decay, gum inflammation, and bleeding problems, that has been generally eradicated in modern western society other than in alcoholics, some elderly people, or those whose diets do not contain fresh fruits and vegetables.
Care must be taken in food preparation to preserve the amount of vitamin C present in a particular food. Vitamin C is water soluble, so actions such as cooking a vitamin C source in water or otherwise soaking the product in water will reduce its vitamin C content. Whole food sources, such as a potato with its skin intact, will preserve greater quantities of vitamin C than processed foods.
Due to its water solubility, vitamin C is not known to create any adverse effects if consumed in larger than recommended quantities, although vitamin C dosages in excess of 2,000 mg per day are not recommended. Linus Pauling (1901–1994), Nobel prize winner in chemistry, was at the forefront of the movement advocating massive daily supplements of vitamin C (amounts in excess of 5,000 mg), as both a potential cold preventative and as an anticancer agent. It was the view of Pauling and others that, because the body does not have the ability to synthesize its own stores of vitamin C (unlike other mammals), large doses would in essence fill a genetic gap. While modern research has confirmed that vitamin C's antioxidant properties will prevent and possibly counteract cell damage, evidence of any greater capabilities is inconclusive.