Vitamin C

Strawberries are a good source of Vitamin C. Source: Public Domain Pictures.

Chemical structure of ascorbic acid. Source: Wikimedia Commons.

Vitamin C is an essential nutrient for the human body. It is required for a variety of chemical reactions.

Other Names

• L-ascorbate
• Ascorbic acid (this is a chemical variant of vitamin C)
• Dehydroascorbic acid

How Vitamin C Works

Vitamin C works as an electron donor, meaning that it gives an electron to other molecules in the body in order to allow chemical reactions to occur. By doing this, vitamin C works as an antioxidant.^[1]

Sources

Humans cannot make vitamin C and must ingest it in their diet.^[1]

Vitamin C is mostly found in fruits and vegetables. An extensive list of foods containing vitamin C is provided by the USDA.^[2]

Selected food sources

Healthful diets

According to the 2005 Dietary Guidelines for Americans, "Nutrient needs should be met primarily through consuming foods. Foods provide an array of nutrients and other compounds that may have beneficial effects on health. In certain cases, fortified foods and dietary supplements may be useful sources of one or more nutrients that otherwise might be consumed in less than recommended amounts. However, dietary supplements, while recommended in some cases, cannot replace a healthful diet."^[3]

Supplements

Vitamin C is available in powder and tablet forms.

Benefits

The clearest benefit of vitamin C is the prevention of scurvy.

Diets rich in fruits and vegetables are associated with a lower risk of cardiovascular disease.^[4][5] It is not known whether vitamin C contributes to these benefits. One theory is that vitamin C has beneficial effects on [Blood Pressure|blood pressure]], which has been demonstrated in some studies.^[6][7]

Vitamin C has also been shown to enhance iron absorption.^[8]

Recommended Daily Intake

In order to meet requirements for many vitamins, including vitamin C, United States Department of Agriculture guidelines recommend the ingestion of at least four and a half cups (nine servings) of fruits and vegetables daily.^[9] If these recommendations are followed, the amount of vitamin C ingested is estimated to be in the 200–300 mg range depending on the specific vitamin C content of the food consumed.

A survey of over 8,000 participants in the 1999-2000 National Health and Nutrition Examination Survey revealed that only 40% of Americans ate more than 5 servings of fruits and vegetables daily. In some groups, far fewer consumed an adequate amount; in adolescent boys, only 0.7% did so.^[10]

Recommendations for vitamin C are provided in the Dietary Reference Intakes (DRIs) developed by the Institute of Medicine (IOM). The recommended dietary allowances (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97% to 98%) healthy individuals in each age and gender group. ^[11]

Recommended dietary allowances (RDAs) for vitamin C

RDAs for vitamin C are listed as milligrams.

Adequate intakes of vitamin C for infants

Information is insufficient to establish an RDA for vitamin C for infants. Adequate intakes (AIs) have been established based on the amount of vitamin C consumed by healthy breast milk.

Vitamin C deficiency

Scurvy results from vitamin C deficiency. This disease is characterized by spongy gums, loosening of the teeth, and bleeding into the skin and mucous membranes. Some of the enzymes to which vitamin C donates electrons are important for the synthesis of collagen. Others help in energy production, hormone production, and metabolism.^[12] Scurvy is lethal if it is not treated. Vitamin C is required for humans to survive.

Many conditions that are associated with oxidation have been associated with low vitamin C levels. Some of these include smoking, diabetes mellitus, and heart attacks. It is not known whether these diseases cause lower vitamin C levels, or whether lower vitamin C levels contribute to the diseases.^[1]

Too much vitamin C

Studies of the blood concentrations of vitamin C associated with supplement intake have shown that 400 mg per day is the most the body can use. When more than this is taken, no additional vitamin C gets into the blood. The excess amount is excreted in the urine.^[1]

Excessive intake of vitamin C can result in the overproduction of oxalate. Excess oxalate excretion in the urine can cause kidney stones.^[13]

Tolerable upper intake levels

Side Effects

At doses recommended by the USDA, vitamin C has not been shown to produce side effects. At higher doses, however, it can have a diuretic effect (making one produce more urine) and at very high doses, it can cause diarrhea, nausea, vomiting, skin rash, flushing, headache, fatigue, and disturbed sleep.^[14]

Risks

High vitamin C levels have been associated with high iron stores in the body, a condition that may be associated with chronic diseases such as diabetes and heart disease.^[15]

Clinical Trials

For a list of clinical trials involving vitamin C, visit Vitamin C Clinical Trials.

Controversy

Debates

Nobel laureate Linus Pauling is commonly known for his advocacy of high doses of vitamin C for preventing illness, particularly the common cold. Debate continues about this today. Some studies have supported this theory,^[16] and some have refuted it.^[17]

History

How Vitamin C was discovered

In 1937, both the Nobel Prize in Chemistry and the Nobel Prize in Medicine went to researchers for their work on vitamin C: the former to Walter Norman Haworth "for his investigations on carbohydrates and vitamin C" and the latter to Albert von Szent-Györgyi Nagyrapolt "for his discoveries in connection with the biological combustion processes, with special reference to vitamin C and the catalysis of fumaric acid".^[18]

Interesting Facts

• Vitamin C is made internally by almost all organisms. Humans, other primates, and guinea pigs are rare exceptions and cannot make their own vitamin C internally.^[1]

References

1. ↑ ^{1.0 1.1 1.2 1.3 1.4} Padayatty S, Katz A, Wang Y, et al. Vitamin C as an antioxidant: evaluation of its role in disease prevention. J Am Coll Nutr. 2003;22 (1): 18-35. Abstract | PDF
2. ↑ USDA Web site. USDA National Nutrient Database for Standard Reference, Release 17: Vitamin C. PDF.
3. ↑ U.S. Department of Health and Human Services, U.S. Department of Agriculture Web site. Dietary Guidelines for Americans 2005. PDF.
4. ↑ He FJ, Nowson CA, MacGregor GA. Fruit and vegetable consumption and stroke: meta-analysis of cohort studies. Lancet. 2006 Jan 28;367(9507):320-6. Abstract
5. ↑ He FJ, Nowson CA, Lucas M, MacGregor GA. Increased consumption of fruit and vegetables is related to a reduced risk of coronary heart disease: meta-analysis of cohort studies. J Hum Hypertens. 2007 Sep;21(9):717-28. Epub 2007 Apr 19. Abstract
6. ↑ Ness AR, Chee D, Elliott P. Vitamin C and blood pressure--an overview. J Hum Hypertens. 1997 Jun;11(6):343-50. Abstract
7. ↑ Brody S, Preut R, Schommer K, Schürmeyer TH. A randomized controlled trial of high dose ascorbic acid for reduction of blood pressure, cortisol, and subjective responses to psychological stress. Psychopharmacology (Berl). 2002 Jan;159(3):319-24. Epub 2001 Nov 20. Abstract
8. ↑ Teucher B, Olivares M, Cori H. Enhancers of iron absorption: ascorbic acid and other organic acids. Int J Vitam Nutr Res. 2004 Nov;74(6):403-19. Abstract
9. ↑ USDA. Chapter 5: Food Groups to Encourage. Dietary Guidelines for Americans 2005.
10. ↑ Guenther PM, Dodd KW, Reedy J, Krebs-Smith SM. Most Americans eat much less than recommended amounts of fruits and vegetables. J Am Diet Assoc. 2006 Sep;106(9):1371-9. Abstract
11. ↑ Institute of Medicine Web site. Dietary Reference Intakes: Vitamins. PDF.
12. ↑ Merriam-Webster Online. Scurvy.
13. ↑ Massey LK, Liebman M, Kynast-Gales SA. Ascorbate increases human oxaluria and kidney stone risk. J Nutr. 2005 Jul;135(7):1673-7. Abstract | Full Text
14. ↑ Ascorbid Acid and Its Potassium and Sodium Salts. Seventeenth Report of the Joint FAO/WHO Expert Committee on Food Additives, World Health Organization. techn. Rep. Ser., 1974, No. 539; FAO Nutrition Meetings Report Series, 1974, No. 53.
15. ↑ Fleming DJ, Tucker KL, Jacques PF, Dallal GE, Wilson PW, Wood RJ. Dietary factors associated with the risk of high iron stores in the elderly Framingham Heart Study cohort. Am J Clin Nutr. 2002;76 (6): 1375-84. Abstract | PDF
16. ↑ Padayatty SJ, Riordan HD, Hewitt SM, Katz A, Hoffer LJ, Levine M. Intravenously administered vitamin C as cancer therapy: three cases. CMAJ. 2006 Mar 28;174(7):937-42. Abstract | Full Text
17. ↑ Assouline S, Miller WH. High-dose vitamin C therapy: renewed hope or false promise? CMAJ. 2006 Mar 28;174(7):956-7. Abstract | Full Text
18. ↑ Nobel Prize Foundation Web site. The Nobel Prize in Chemistry 1937 and The Nobel Prize in Physiology or Medicine 1937.

External Links

Institute of Medicine

USDA: National Nutrient Database for Standard Reference