Problems with estimating vitamin C intakes.

Abstract

The vitamin C content of foods was examined from two national databases and new values were obtained by HPLC. HPLC values were lower in four of the five highest vitamin C contributors to the US diet (orange juice, grapefruit, tomatoes and tomato juice, and potatoes), as well as in broccoli, red peppers, and cooked collard and mustard greens, compared with values from the other databases. When HPLC values were substituted in the Health Habits and History Questionnaire, the resulting estimates of dietary intake of vitamin C in two studies were lower. Despite these lower estimates of absolute intake, in one study the correlation between dietary vitamin C and plasma ascorbic acid was similar. In conclusion, the accuracy of the vitamin C content of foods is important for estimating the absolute amount of vitamin C intake in the population but may not change the ranking of people in epidemiological studies.