Vitamin C content of foods: sample variability.

A recent survey of foods that constitute the major sources of vitamin C in the American diet yielded information on the total content of this vitamin as well as the amount of its two forms, ascorbic acid and dehydroascorbic acid (DHAA) in these foods. Samples of individual foods showed a surprising large range of vitamin content even for foods collected from the same regions of the country and from the same source. The amount of DHAA in the different foods varied from approximately 10% to 20% of the total vitamin content. The large range of values for the vitamin content in a given food suggests further that in human-diet studies, when the major sources of vitamin C are from a few foods, daily analyses are required for the necessary precision.