Ascorbic acid is readily absorbed from the intestines, ideally about 80–90 percent of that ingested. It is used by the body in about two hours and then usually out of the blood within three to four hours. For this reason, it is suggested that vitamin C supplements be taken at four-hour intervals rather than once a day; or it may be taken as time-released ascorbic acid. Vitamin C is used up even more rapidly under stressful conditions, with alcohol use, and with smoking. Vitamin C blood levels of smokers are much lower than those of nonsmokers given the same intakes. Other situations and substances that reduce absorption or increase utilization include fever, viral illness, antibiotics, cortisone, aspirin and other pain medicines, environmental toxins such as DDT, petroleum products, or carbon monoxide, and exposure to heavy metals such as lead, mercury, or cadmium. Sulfa antibiotics increase elimination of vitamin C from the body by two to three times.

Some ascorbic acid is stored in the body, where it seems to concentrate in the organs of higher metabolic activity. These include the adrenal glands (about 30 mg.), pituitary, brain, eyes, ovaries, and testes. A total of about 30 mg. per pound of body weight. We likely need at least 200 mg. a day in our diet to maintain body stores—much more if we smoke, drink alcohol, are under stress, have allergies, are elderly, or have diabetes.

Vitamin C is a very complex and important vitamin. The recommended amounts vary more widely than those for any other nutrient, ranging from 100–80 or 100 grams daily, depending on the condition. C is also the most commonly supplemented vitamin among the general public, because of either the popular press or its good effect, or because of the other common C—the "cold."

Sources: The best-known sources of vitamin C are the citrus fruits—oranges, lemons, limes, tangerines, and grapefruits. The fruits with the highest natural concentrations are citrus fruits, rose hips, and acerola cherries, followed by papayas, cantaloupes, and strawberries. Good vegetable sources include red and green peppers (the best), broccoli, Brussels sprouts, tomatoes, asparagus, parsley, dark leafy greens, cabbage, and sauerkraut. There is not much available in the whole grains, seeds, and beans; however, when these are sprouted, their vitamin C content shoots up. Sprouts, then, are good foods for winter and early spring, when other fresh fruits and vegetables are not as available. Animal foods contain almost no vitamin C; though fish, if eaten raw, has enough to prevent deficiency symptoms.

Natural vitamin C supplements are usually made from rose hips, acerola cherries, peppers, or citrus fruits. Vitamin C can be synthesized from corn syrup, which is high in dextrose, much as it is made from glucose in most other animals’ bodies. Synthetic ascorbic acid, though it can be concentrated for higher doses than natural extracts, is still usually made from food sources. Sago palm is another fairly new source of vitamin C supplements. It is used primarily as a lower allergenic source than the corn-extracted ascorbic acid.

Functions: One important function of vitamin C is in the formation and maintenance of collagen, the basis of connective tissue, which is found in skin, ligaments, cartilage, vertebral discs, joint linings, capillary walls, and the bones and teeth. Collagen, and thus vitamin C, is needed to give support and shape to the body, to help wounds heal, and to maintain healthy blood vessels. Specifically, ascorbic acid works as a coenzyme to convert proline and lysine to hydroxyproline and hydroxylysine, both important to the collagen structure.