Vitamin C (a.k.a. ascorbic acid) made its worldly debut in the 16th century when sailors discovered that by eating citrus fruit on voyages, they could prevent scurvy, even though they did not realize it was the vitamin C that was preventing the disease. English sailors of the 18th century carried limes on board their ships for this reason, which is how they became known as "limeys." The recognized benefits of vitamin C have been broadened beyond avoiding nutrient deficiency and have been linked to curing the common cold, lowering blood pressure, reducing the risks of heart disease and cancer, reducing diabetes complications, assisting lung function and enhancing immune function. Vitamin C definitely keeps scurvy at bay, but the other benefits that have been attributed to this powerful antioxidant have not been proven definitively, though numerous studies certainly point to the fact that vitamin C is integral to staying healthy.
Vitamin C prevents scurvy by helping the body produce collagen, the protein that makes up the connective tissues of the body. Vitamin C deficiency leads to a lack of collagen, which causes the connective tissues to break down. For this reason, those suffering from scurvy face broken blood vessels, bleeding gums, loose teeth, weakness, fluid retention and anemia. One paper called "Vitamin C and Vascular Disease," published by Ron Kennedy, M.D., (based on the works of Linus Pauling and Matthias Rath), expands this theory to attribute vitamin C with the prevention of heart disease. Vitamin C deficiency does not immediately lead to broken blood vessels and death. The first thing that happens is a weakening of the blood vessel walls, which manifests in cracking. These cracks, if they cannot be repaired with collagen because of a lack of vitamin C, are blocked with lipoprotein(a), which is a collection of fat and cholesterol molecules surrounded by a layer of protein. While this is effective at warding off scurvy, the lipoprotein(a) attracts other lipoproteins to it, and the collection of cholesterol and fat eventually leaks into the blood stream of the vessel they protect constricting it. This clogging effect is what leads to blood vessel disease, high blood pressure and eventually heart attack or heart disease.
A study published in the September 1996 American Journal of Epidemiology supports Kennedy's theory. The study examined 747 elderly people (age 60+) for nine to 12 years, focusing on food intake and vitamin C, vitamin E and beta-carotene levels in the blood. Those with daily intakes of vitamin C of 400 mg and higher had a lower incidence of death from heart disease than the other study participants. Another study, published in the British Medical Journal in 1995, determined that of 730 study participants, those with high intakes of vitamin C had a much reduced incidence of death from stroke than those participants with lower vitamin C intake levels.
In terms of cancer prevention, vitamin C has been widely studied. A review article published in the 1991 American Journal of Clinical Nutrition (54:13105-13145) stated that of 90 epidemiologic studies examining the role of vitamin C in cancer prevention, "the vast majority have found statistically significant protective effects:" However, several studies demonstrate that vitamin C has no effect on cancer. For example, one study described in the 1996 Journal of the National Cancer Institute (88:340-348) stated that there was no association between breast cancer risk and intake of vitamin C. Another study published in the same journal in 1993 (85:1483-1492) stated that vitamin C consumption had no significant effect on mortality rates from stomach and esophagus cancers.
Researchers are also reviewing vitamin C's relation to stress. There are only four species of mammals that cannot produce ascorbate in the body - fruit bats, gorillas, guinea pigs and humans. During times of stress, it has been noted that animal species produce higher amounts of their natural ascorbate to ward off disease, infection or emotional stress, according to Kennedy. A study conducted by P Samuel Campbell of the University of Alabama-Huntsville, which was presented at the 1999 American Chemical Society conference, demonstrated that with vitamin C supplementation, stress hormone secretion and other signs of stress in rats were reduced. The study also concluded that rats, and perhaps people, under emotional stress might benefit from higher doses of vitamin C to protect immune function.
However, not all vitamin C supplements contain the same amount of vitamin C, and the vitamin C in the supplements can come in different forms. The most common forms of vitamin C in supplements are ascorbic acid, calcium ascorbate, sodium ascorbate or a combination of those. Vitamin C is absorbed by the body in the digestive tract and then reabsorbed by the kidneys, so supplements must break down to be utilized by the body. If the ascorbic acid in a supplement does not break down efficiently, the body cannot use it, and it will be excreted. In addition, high doses of ascorbic acid are not likely to be completely absorbed, so it is preferable to take divided doses of the vitamin throughout the day instead of a single large dose.
The recommended daily allowance (RDA) of vitamin C was increased in April 2000 by the Institute of Medicine. The RDA is set now at 90 mg/d for men and 75 mg/d for women, adding an additional 35 mg/d for smokers. The Tolerable Upper Intake Level was set at 2 g/d. Good sources of vitamin C are citrus fruits, broccoli, Brussels sprouts, cabbage, green peppers, potatoes, spinach, strawberries, sweet peppers, hot peppers and tomatoes. Overdoses of vitamin C can lead to headaches, stomach cramps, nausea, vomiting, diarrhea and kidney stones. In rare cases, taking high amounts of vitamin C during pregnancy and abruptly withdrawing from supplementation can lead to rebound scurvy in both the mother and the baby. People with blood disorders or problems with kidney stones should avoid high doses of vitamin C.