Vitamin C Health Article

Preparations

The U.S. recommended dietary allowance (RDA) of vitamin C was changed in 2000 to reflect growing recognition of the importance of vitamin C in the diet as an antioxidant as well as a protection against deficiency. The new values are as follows:

• men: 90 mg
• women: 75 mg
• pregnant women: 80 mg
• lactating women: 95 mg
• smokers: should consume an additional 35 mg

The National Academy of Sciences also established for the first time an upper limit (UL), or maximum daily dose, of 2,000 mg. Daily values for the vitamin as recommended by the U.S. Food and Drug Administration, the values listed on food and beverage labeling, remain at 60 mg for both men and women age four and older.

Many fruits and vegetables, including citrus fruits and berries, are rich in vitamin C. Foods rich in vitamin C include raw red peppers (174 mg/cup), guava (165 mg/fruit), orange juice (124 mg/cup), and black currants (202 mg/cup). Rose hips, broccoli, tomatoes, strawberries, papaya, lemons, kiwis, and brussels sprouts are also good sources of vitamin C. Eating at least five to nine servings of fruits and vegetables daily should provide adequate vitamin C intake for most people. Fresh, raw fruits and vegetables contain the highest levels of the vitamin. Both heat and light can reduce vitamin C potency in fresh foods, so overcooking and improper storage should be avoided. Sliced and chopped foods have more of their surface exposed to light, so keeping vegetables and fruits whole may also help to maintain full vitamin potency.

Vitamin C supplements are another common source of the vitamin. Individuals at risk for vitamin C depletion such as smokers, women who take birth control pills, and those with unhealthy dietary habits may benefit from a daily supplement. Supplements are available in a variety of different forms including pills, capsules, powders, and liquids. Vitamin C formulas also vary. Common compounds include ascorbic acid, calcium ascorbate, sodium ascorbate, and C complex. The C complex compound contains a substance called bioflavonoids, which may enhance the benefits of vitamin C. Vitamin C is also available commercially as one ingredient of a multivitamin formula.

The recommended daily dosage of vitamin C varies by individual need, but an average daily dose might be 200 mg. Some healthcare providers recommend megadoses (up to 40 g) of vitamin C to combat infections. However, the efficacy of these megadoses has not been proven, and in fact, some studies have shown that doses above 200 mg are not absorbed by the body and are instead excreted.

Precautions

Overdoses of vitamin C can cause nausea, diarrhea, stomach cramps, skin rashes, and excessive urination.

Because of an increased risk of kidney damage, persons with a history of kidney disease or kidney stones should never take dosages above 200 mg daily, and should consult with their healthcare provider before starting vitamin C supplementation.

A 1998 study linked overdoses (above 500 mg) of vitamin C to cell and DNA damage. However, other studies have contradicted these findings, and further research is needed to establish whether high doses of vitamin C can cause cell damage.

Side effects

Vitamin C can cause diarrhea and nausea. In some cases, side effects may be decreased or eliminated by adjusting the dosage of vitamin C.

Interactions

Vitamin C increases iron absorption, and is frequently prescribed with or added to commercial iron supplements for this reason.

Individuals taking anticoagulant, or blood thinning, medications should speak with their doctor before taking vitamin C supplements, as large doses of vitamin C may impact their efficacy.

Large amounts of vitamin C may increase estrogen levels in women taking hormone supplements or birth control medications, especially if both the supplement and the medication are taken simultaneously. Women should speak with their doctor before taking vitamin C if they are taking estrogen-containing medications. Estrogen actually decreases absorption of vitamin C, so larger doses of vitamin C may be necessary. A healthcare provider can recommend proper dosages and the correct administration of medication and supplement.

Persons who take aspirin, antibiotics, and/or steroids should consult with their healthcare provider about adequate dosages of vitamin C. These medications can increase the need for higher vitamin C doses.

Large dosages of vitamin C can cause a false-positive result in tests for diabetes.

BOOKS

Reavley, Nocola. The New Encyclopedia of Vitamins, Minerals, Supplements, and Herbs. New York: M. Evans & Company, 1998.