Intakes of vitamin C
In previous sections reference has been made to pharmacologic doses of ascorbic acid. Fortunately it is relatively nontoxic, considering the recent use of megadoses of ascorbic acid for colds, and the infrequency of reports of adverse reactions to these doses. However, SO.~le adverse effects have been reported.32 Gastrointestinal disturbances, including nausea, cramps, and, especially, diarrhea are most frequent.33 Increased excretion of uric acid,34 impaired bactericidal activity ofleukocytes,35 and absorption of excessive amounts of food iron36 are undesirable effects that have been demonstrated under wellcontrolled experimental conditions. There is also evidence that prolonged high intakes of ascorbic acid may affect the body's catabolic and excretory systems, leading to a higher than normal need for the vitamin, which persists after the intake of large doses is discontinued. Not only have such effects been reported in adults, but rebound scurvy has been observed in infants whose mothers were consuming large amounts of vitamin C during pregnancy.
After reviewing the current evidence of the effects of high intakes of ascorbic acid on the common cold and other diseases, the Food and Nutrition Board concluded that the demonstrated benefits are minor and do not justifY recommending routine intake of pharmacologic doses of ascorbic acid.
Food sources
It is obvious from the bar chart (Fig. 8-3) that the commonly used fruits and vegetables of Group 3 are the richest sources of ascorbic acid, with citrus fruits, strawberries, cantaloupe, and a number of raw, leafY vegetables topping the list. Canned or frozen ci trus juice may be the cheapest source of vitamin C when fresh citrus fruit is scarce or expensive and may be cheaper than tomato juice because it takes three times as much tomato as citrusjuice to supply the same amounts of vitamin C.
Many factors affect the ascorbic acid content offruic; and vegetables; variety, maturity, length of storage, par.: of the plant, seasonal and geographical factors are aL influential. As plants mature they generally have Iow ascorbic acid; the sprouts of beans or grains, however, d contain vitamin C. Exposure to sunlight also tends increase the plant's ascorbic acid content. Food value tables give average representative amounts, whereas any individual food may vary considerably from this value.37 From analyses ofthe ascorbic acid content of such foods as potatoes, cabbage, and broccoli purchased during the winter in northern Vermont, the authors38 conclude "that certain vegetables, as purchased during the winter months, provide dependable quantities of total ascorbic acid, even though they have been subjected to transportation, storage, and handling."In some countries indigenous frui ts high in vitamin C are overlooked, even though they are readily available. For example, in Puerto Rico the acerola (azarole, or West Indian cherry) has the highest ascorbic acid content of any known food.39 Only after attention had been called to it, did the acerola become popular in that country. In Great Britain during World War II rosehip and black-currant syrups or jams served to supplement the meager supply of vi tamin C from garden vegetables. Even before the war, in nC1;thern Russia an extract of pine needles rich in vitamin C was being added to berry juice as a health beverage for school children. In another part of northern Europe raw turnip juice saved the lives of many infants who othenvise would have died of scurvy. Depending on diet, human milk may contain more ascorbic acid than average cow's milk and considerably more than is found in pasteurized milk, thereby affecting the amount and the timing of additional sources needed in an infant's diet
