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Four food-frequency categories of fruit intake as a predictor of plasma ascorbic acid level in middle-aged Japanese
S Tsugane1, M T Fahey, M Kobayashi
1Epidemiology and Biostatistics Division, National Cancer Center Research Institute East, Kashiwa, Chiba, Japan. stsugane@east.ncc.go.jp
Purpose:
Plasma levels of ascorbic acid are assumed to be determined not only by dietary amount of ingested vitamin C, but also by other dietary and nondietary factors. To assess the predictability of plasma ascorbic acid level in Japanese men, we examined its association with dietary sources of vitamin C and other lifestyle factors.
Methods:
In a cross-sectional study of 621 healthy men aged 40-49 years who were sampled randomly from five areas in Japan, the weekly intake frequency of foods rich in vitamin C (< 1, 1-2, 3-4, > or = 5 days/week), alcohol consumption per week, use of vitamin C supplements, and smoking were assessed by use of a food-frequency questionnaire (FFQ) (all subjects) and a 3-day weighed dietary record (DR) from 203 volunteers.
Results:
In univariate analyses of FFQ data, the intake frequency of fruit (R2 = 0.12), pickled vegetables (R2 = 0.03), potatoes (R2 = 0.01), and alcohol consumption (R2 = 0.02) were significant determinants of plasma ascorbic acid in addition to supplement use and study area. In a multivariate analysis, four FFQ categories of fruit intake accounted for 19% of the variation in plasma ascorbic acid among nonsupplement users after adjustment for study area and alcohol intake. The association between plasma ascorbic acid level and quartile of dietary vitamin C intake (mg/day) measured by DR was weaker (R2 = 0.04) than the association between plasma ascorbic acid level and dietary intake of fresh fruit (g/day) (R2 = 0.09).
Conclusion:
The predictability of plasma ascorbic acid by a four-category FFQ assessment of fruit intake was superior to calculated vitamin C or fruit intake assessed by detailed DR.