Vitamins & Minerals
What Is Night Blindness?
Vitamin C is a water-soluble vitamin that has a number of biological functions.
Where is it found?
Who is likely to be deficient?
People with kidney failure have an increased risk of vitamin C deficiency. However, people with kidney failure should take vitamin C only under the supervision of a doctor, as excessive vitamin C intake can be toxic in people who cannot excrete it properly.
How much is usually taken?
Some scientists have recommended that healthy people take multi-gram amounts of vitamin C for the prevention of illness. However, little or no research supports this point of view and it remains controversial. Supplementing more results in an excretion level virtually identical to intake, meaning that consuming more vitamin C does not increase the amount that remains in the body. On the basis of extensive analysis of published vitamin C studies, researchers at the Linus Pauling Institute at Oregon State University have called for the RDA to be increased, but only to 120 mg. This same report reveals that “. . . 90 to 100 mg vitamin C per day is required for optimum reduction of chronic disease risk in nonsmoking men and women.” Thus, the multiple gram amounts of vitamin C taken by many healthy people may be superfluous.
The studies that ascertained approximately 120–200 mg daily of vitamin C is correct for prevention purposes in healthy people have typically not investigated whether people suffering from various diseases can benefit from larger amounts. In the case of the common cold, a review of published trials found that amounts of 2 grams per day in children appear to be more effective than 1 gram per day in adults, suggesting that large intakes of vitamin C may be more effective than smaller amounts, at least for this condition
Are there any side effects or interactions?
Vitamin C increases iron absorption and should be avoided by people with iron-overload diseases (for example, hemochromatosis, hemosiderosis). People with the following conditions should consult their doctor before supplementing with vitamin C: glucose-6-phosphate dehydrogenase deficiency, iron overload (hemosiderosis or hemochromatosis), history of kidney stones, or kidney failure.
As vitamin C may react with certain medicines, people undergoing treatment should consult with their doctor or pharmacist before adding the nutrient to their self-care regimen.