Vitamin C plays an important role in many biochemical reactions in the body; adequate levels improve iron absorption (but do not result in overabsorption in otherwise healthy persons), whereas inadequate levels can lead to scurvy. The current recommended daily allowance (RDA) of vitamin C is 60 mg per day, but this recommendation was established nearly 20 years ago on the basis of incomplete experimental data. Levine and colleagues reviewed new recommendations for vitamin C intake that were established by the Food and Nutrition Board of the National Academy of Sciences.

The U.S. Department of Agriculture and the U.S. National Cancer Institute recommend that persons consume at least five servings of fruits and vegetables per day. For a list of food sources rich in vitamin C, see the accompanying table on page 2117. Consumption at this level increases intake of vitamin C to at least 210 mg per day. Nutrition surveys indicate that the actual amount currently ingested is between 73 and 84 mg per day. Vitamin C is associated with few toxic effects, and these generally are related to dosage. For example, diarrhea and abdominal bloating are related to dosage. Dosages of more than 1 g per day should be avoided because at that level adverse effects can occur. A number of toxic effects have been attributed to vitamin C in error, including hypoglycemia, infertility, mutagenesis and vitamin B₁₂ destruction.

The authors conclude by listing the new recommendations about vitamin C intake established by the Food and Nutrition Board of the National Academy of Sciences. The concept of the RDA has been expanded to new guidelines, called Dietary Reference Intakes, which are a combination of estimated average requirement, RDA, adequate intake and tolerable upper intake level. For vitamin C, the recommended intake is between 100 and 200 mg per day. The authors also emphasize that five daily servings of fruits and vegetables should continue to be the principal source of vitamin C.