Vitamin C is a water-soluble vitamin that is essential to the maintenance of several body functions. Because humans cannot synthesize vitamin C, it has to be provided from the diet. Vitamin C is absorbed in the small intestine but is poorly stored in the body. This means that it must be consumed on a daily basis in order to prevent deficiency.
Vitamin C is an important nutrient that plays a vital role in the production and maintenance of the protein, collagen. Collagen is the foundation material of the connective tissue, which is important for healthy skin, bones, teeth, tendons, and blood vessels. It is also essential for wound healing. However, vitamin C performs many other functions in the body. It participates in the synthesis of several compounds such as hormones, bile, and DNA; boosts immune function, enhancing the body’s ability to fight infections; and enhances iron absorption.
In addition, vitamin C seems to present antioxidant properties, protecting the body against the damage caused by free radicals.[1] The ability to neutralize free radicals appears to have a potential protective effect against certain cancers, heart disease, and cataracts.
Despite the popular belief that taking large doses of vitamin C may help prevent colds, recent researches point out that it is not the case. Several reliable experiments showed that vitamin C supplementation has an almost insignificant effect on common colds, though it may shorten the duration of a cold by one day and slightly reduce its symptoms. This means that taking megadoses of vitamin C is not only useless but can also be dangerous.
The truth is that our body can only handle a small amount of this vitamin at a time, and the ingestion of large amounts reduces absorption. All excess is usually eliminated in urine and feces. However, megadoses are potentially toxic, causing diarrhea and stomach inflammation.
Vitamin C deficiency, although uncommon nowadays, cause a disease called scurvy, which leads to weakness, slow wound healing, bleeding gums, and bone pain, among other symptoms. To develop symptoms of the deficiency, a person must go without vitamin C for 20 to 40 days. Today, deficiency is most commonly seen in alcoholic people who have poor diets and older adults with inadequate food intake.
The Recommended Dietary Allowance (RDA) for adults is between 75 and 90 milligrams per day. Keep in mind that most of the vitamin C (70% to 90%) is absorbed when you consume between 30 and 180 milligrams per day. Ingesting larger doses decrease absorption considerably.[2] Moreover, vitamin C excretion starts at intakes of 100 milligrams and, at 500 milligrams, almost everything consumed is excreted. However, because of its antioxidant properties, smokers are advised to consume a little extra vitamin C (an additional 35 milligrams per day) to combat the negative effects of the toxic by-products of cigarette smoke. The upper level is 2 grams per day and consuming more than that may have side effects.
Vitamin C is widely available in fruits and vegetables. Major sources are citrus fruits, bell peppers, Brussels sprouts, cauliflower, broccoli, and strawberries, among others. Generally, the consumption of two servings of any these foods per day provides the recommended amount of vitamin C. Vitamin C may also be added to processed foods (ready-to-eat cereals) and beverages (fruit drinks). In these cases, the vitamin C content is required to appear on the Nutrition Facts panel. Keep in mind that a Daily Value of 5% or less is considered low, while 20% or more is considered high. A fact that should be brought to attention is that vitamin C is a sensitive nutrient and may be destroyed with improper storage and excessive cooking. This means that fruits and vegetables should be kept in the refrigerator,[3] stored in air-tight containers, minimally manipulated, and gently cooked (microwave or steamed).
References
Boyle, M. and Long, S. Personal Nutrition. Belmont, CA: Wadsworth Cengage Learning. 2010.
Wardlaw, G. and Smith, A. Contemporary Nutrition. New York: McGraw-Hill. 2009.
[1] Free radicals are highly toxic compounds that can be formed from sunlight, cigarette smoke, pollution, stress, and many other chemical reactions in the body.
[2] Ingesting 1,000 milligrams of vitamin C per day reduce its absorption to around 50%.
[3] Exceptions are potatoes, tomatoes, onions, and bananas.