Vitamin C

Other Name(s):

anti-scorbutic agent, ascorbic acid, calcium ascorbate, dehydroascorbic acid, sodium ascorbate

General Description:

Vitamin C (ascorbic acid) is a water-soluble vitamin found in many fruits and vegetables. It is a popular supplement, and many people feel that large doses (megadoses) provide additional benefits for the body. Vitamin C is important in the development and maintenance of the connective tissues of the body. Vitamin C is also a potent antioxidant. Some studies show that vitamin C may help reduce the symptoms and length of the common cold.

Vitamin C plays many roles in the chemistry of the human body. It is essential for the production of collagen, a critical constituent of the body's connective tissue. It is also necessary for the production of hemoglobin, the oxygen-carrying pigment inside red blood cells, and it helps increase the absorption of iron from the intestines.

The body uses vitamin C to produce other important chemicals such as carnitine, tyrosine, steroids made in the adrenal gland and neurotransmitters (agents used in the conduction of nerve impulses and between synapses). Vitamin C is necessary for the function of many enzyme systems. It is involved in converting folic acid to its more active form, tetrahydrofolic acid, and preventing its degradation into inactive metabolites that are no longer useful to the body.

Vitamin C is also a potent antioxidant. Antioxidants are thought to play a role in slowing the aging process, reducing damage to the lining of blood vessels and possibly reducing the incidences of some types of cancer. Although these roles have not been entirely substantiated, increasing evidence shows that vitamin C has some function in all of these processes.

Medically Valid Uses:

Prior to the discovery of vitamin C, a disease called scurvy affected people who had little access to fresh fruits and vegetables. Scurvy was particularly common among sailors away at sea for months at a time. When it was discovered that eating limes could prevent scurvy, British sailors were nicknamed "Limeys." Later, vitamin C was discovered and was used to prevent and treat scurvy. Today, vitamin C supplements are taken to ensure that an individual meets the daily requirement of vitamin C, even if the diet is poor.

Research, particularly that sponsored by Dr. Linus Pauling, two-time Nobel Prize winner, suggests that vitamin C plays a role in decreasing the symptoms and reducing the duration of the common cold. Colds are the most common upper-respiratory infection and account for the greatest number of missed workdays. The benefits of reducing the length of a cold even by a day or two with the use of vitamin C are great. However, although it can reduce symptoms and shorten a cold, vitamin C probably does not prevent colds.

Unsubstantiated Claims:

Please note that this section reports on claims that have NOT yet been substantiated through scientific studies.

Vitamin C is claimed to help prevent or cure gum disease (periodontitis) and various types of cancer, protect the body against effects of pollution, prevent blood clots and minimize bruising.

Recommended Intake:

As indicated below, vitamin C is measured in milligrams (mg). Tablets and chewable tablets are the most popular forms. Vitamin C is also available in time-release capsules, powder (generally as sodium ascorbate), lozenges, oral liquid and injections. The RDA is the recommended dietary allowance. However, based on recent literature suggesting that 60 mg a day of vitamin C is insufficient for the average adult, the FDA is considering changing the adult requirement to 120 mg a day.

Group

RDA

Breast-feeding women (1st 6 months)

95 mg

Breast-feeding women (2nd 6 months)

90 mg

Adults (over 18 years old)

The U.S. Food and Nutrition Board of the Institute of Medicine recommends a daily intake of 90 milligrams for men older than 18; for women older than 18, the recommendation is 75 milligrams per day; for pregnant women older than 18, 85 milligrams per day; for breast-feeding women older than 18, 120 milligrams per day. Recently, some experts have questioned whether the recommended daily intake should be raised. Other experts have recommended higher intake in some individuals, such as smokers, who should have an additional 35 milligrams per day.

The upper limit of intake should not exceed 2,000 milligrams per day in men or women older than 18, including pregnant or breast-feeding women.

Vitamin C administered by mouth or injection is effective for curing scurvy. In adults, 100 to 250 milligrams by mouth four times daily for one week is generally sufficient to improve symptoms and replenish body vitamin C stores. Some experts have recommended 1 to 2 grams per day for two days followed by 500 milligrams per day for one week. Symptoms should begin to improve within 24 to 48 hours, with resolution within seven days. Treatment should be under strict medical supervision. For asymptomatic vitamin C deficiency, lower daily doses may be used.

Children (under 18 years old)

Adequate Intakes (AIs) and U.S. Dietary Reference Intakes (DRIs) for infants ages 0 to 6 months-old is 40 milligrams per day, and for infants 7 to 12 months old is 50 milligrams per day. The DRI for children 1 to 3 years old is 15 milligrams per day; for 4- to 8-year-olds, the DRI is 25 milligrams per day; for 9- to 13-year-olds, the DRI is 45 milligrams per day; for 14- to 18-year-old males, the DRI is 75 milligrams per day; for 14- to18-year-old females, the DRI is 65 milligrams per day; for 14- to 18-year-old pregnant females, the DRI is 80 milligrams per day; for 14- to18-year-old breast-feeding females, the DRI is 115 milligrams per day. Recently, some experts have questioned whether recommended daily intakes should be raised.

Tolerable Upper Intake Levels (ULs) have not been determined for infants ages 0 to 12 months, and vitamin C in this group should only be derived from food intake to avoid excess doses. The UL for children ages 1 to 3 years old is 400 milligrams per day; the UL for ages 4 to 8 years old is 650 milligrams per day; the UL for ages 9 to 13 years old is 1,200 milligrams per day; the UL for ages 14 to18 years old is 1,000 milligrams per day (including pregnant or breast-feeding females).

Vitamin C is sensitive to light and oxygen in the atmosphere. Vitamin C supplements should therefore be stored in light-resistant containers at room temperature or in the refrigerator, but not frozen. Do not store in metal containers.

Many fruits and vegetables supply vitamin C. The following table represents only a sampling of sources.

Food source

Nutrient content per 100 grams

Parsley

172 mg

Black currants

136 mg

Peppers

128 mg

Horseradishes

120 mg

Broccoli

113 mg

Brussels sprouts

100 mg

Cauliflower

78 mg

Strawberries

60 mg

Spinach

51 mg

Oranges

50 mg

Vitamin C is the most labile nutrient: it is readily changed or broken down in handling, storing or cooking. Fresh produce yields the highest levels of vitamin C. If vegetables are wilted or withered, the vitamin C levels will be significantly reduced. Fresh potatoes have a high vitamin C content, but winter storage reduces the level to only a fifth of the original content, and boiling reduces it even further.

High temperatures accelerate the breakdown of vitamin C in the presence of oxygen or light. Cooking fruits and vegetables destroys much of the vitamin C activity. For highest vitamin C activity, fruits and vegetables should be eaten raw or only lightly cooked.

Need for vitamin C supplements can be caused by inadequate diet with insufficient fresh fruits and vegetables or by moderate to heavy use of alcohol or other drugs.

Continuous exposure to cold climates, particularly working outdoors in very cold weather, or strenuous physical labor or activity, such as heavy manual labor or athletics, may also require vitamin C supplements. Emotional or physical stress, prolonged illness or major surgery also increases the need for this vitamin.

People who have hyperactive thyroid gland (thyrotoxicosis), no stomach acid (achlorhydria) or have had removal of part or all of the stomach (gastrectomy) may need additional vitamin C.

Women who are pregnant or breast-feeding may need to take vitamin supplements, but must consult a physician before doing so.

The syndrome associated with vitamin C deficiency is called scurvy. Scurvy is characterized by a marked tendency to bleeding, especially of the gums, skin, muscles and internal organs.

Other symptoms of vitamin C deficiency include slow healing of wounds, the inability to heal injuries, rough fissured skin, changes in the bones, joint pain and fluid in the joints, and enlargement of the hair follicles, with a build-up of skin at the base of the hair.

Vitamin C deficiency may also result in anemia and fatigue.

Side Effects, Toxicity and Interactions:

There are no side effects associated with reasonable doses of vitamin C. Excess vitamin C is excreted in the urine. Nevertheless, side effects from excessive vitamin C intake may include abdominal pain or cramping, nausea or vomiting, diarrhea, increased urine output (polyuria) and blood in the urine (often microscopic and not usually visible to the human eye). High doses can also aggravate kidney stones in people prone to them.

Some vitamin C preparations contain sulfites or tartrazine. Be sure your vitamin C supplement contains neither of those chemicals if you are allergic to them.

Drug Interactions:

Vitamin C may increase adverse effects associated with acetaminophen or aluminum-containing antacids such as aluminum hydroxide (Maalox, Gaviscon).

Vitamin C may increase blood levels and adverse effects of aspirin, and aspirin may decrease blood levels of vitamin C.

The effects of vitamin C may be decreased by barbiturates including phenobarbital (Luminal, Donnatal), pentobarbital (Nembutal), or secobarbital (Seconal).

Vitamin C supplementation may decrease levels of the drug fluphenazine in the body.

Concomitant administration of high doses of vitamin C can reduce steady-state indinavir plasma concentrations.

There is limited case report evidence that high-dose vitamin C may reduce side effects of levodopa therapy such as nausea or malcoordination.

Nicotine products such as cigarettes, cigars, chewing tobacco, or nicotine patches may decrease the effects of vitamin C.

Oral estrogens may decrease the effects of vitamin C in the body. When taken with ethinyl estradiol, vitamin C may increase blood levels of this drug.

The effects of vitamin C may be decreased by tetracycline antibiotics such as doxycycline (Vibramycin), minocycline (Minocin), or tetracycline (Sumycin).

Vitamin C in high doses appears to interfere with the blood-thinning effects of warfarin by lowering prothrombin time (PT), as noted in case reports in the 1970s. Complications have not been reported (such as increased blood clots).

High doses of vitamin C are not recommended in patients with kidney failure. Caution is advised when taking vitamin C and drugs that may damage the kidneys because of an increased risk for kidney failure.

Interactions with Herbs and Dietary Supplements:

When taken with iron, vitamin C may increase the absorption of iron in the gastrointestinal tract, although this effect appears to be variable and may not be clinically significant.

Vitamin C may increase absorption of lutein vitamin supplements.

Large doses of vitamin C may interfere with the absorption and metabolism of vitamin B12.

In theory, large doses of vitamin C may also interact with herbs and supplements with hormonal, antibacterial, and blood-thinning (anticoagulant) activity.

Additional Information:

Click here for a list of reputable Web sites with general information on nutrition.

References:

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  10. Vitamin C. Facts and Comparisons. St Louis, MO: Facts & Comparisons; 1991.

  11. Vitamin C. The Pharmacist's Guide to Vitamins, Minerals, Herb and Other Nutrients. Austin, TX: American Botanical Council; 1997.

  12. Jacques PF, Taylor A, Hankinson SE, et al. Long-term vitamin C supplement use and prevalence of early age-related lens opacities. Am J Clin Nutr. 1997;66(4):911-6.

  13. Winklhofer-Roob BM, Ellemunter H, Frhwirth M, et al. Plasma vitamin C concentrations in patients with cystic fibrosis: evidence of associations with lung inflammation. Am J Clin Nutr. 1997;65(6):1858-66.

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