Recommended dietary allowance for vitamin C in the United States is also applicable to a population of young Japanese women.
The recommended dietary allowance (RDA) for ascorbic acid (AA) in Canada and the United States has been set for several years at 75 mg/day for women 19-30 years old. Recently this level was questioned, and an increase to 90 mg/day was suggested. For Japanese women in the same age group, we found that the RDA for AA is currently 100 mg/day. Our goal was to determine which RDA is sufficient for maintaining a serum concentration of AA in young Japanese women above the lower reference limit of 7.0 mg/L. We measured serum AA concentrations by an ascorbate oxidase method in 176 healthy Japanese women (19-26 years old). We also performed an ROC analysis to estimate the optimal cutoff value for oral dosage to distinguish individuals with hypovitaminosis-C (<7.0 mg/L) from those with a normal serum AA. We evaluated the Japanese RDA using the 75 or 90 mg/day U.S. RDA and the weight ratio between Japanese and U.S. women, and discovered that the RDA value ranged between 66 and 79 mg/day. From the ROC analysis, we found that the optimal daily dosage of AA is approximately 75 mg/day. This value gave the highest efficiency, sensitivity, negative predictive value, and positive likelihood ratio, and the lowest negative likelihood ratio. Therefore, an RDA of 100 mg/day may be unnecessarily high for young Japanese women.
Ihara
Hiroshi
H
Department of Laboratory Medicine, Ohashi Hospital, School of Medicine, Toho University, 2-17-6 Ohashi, Meguro, Tokyo 153-8515, Japan. ihara@med.toho-u.ac.jp
Shino
Yoshio
Y
Hashizume
Naotaka
N
D000328:Adult; D001205:Ascorbic Acid / Q000008:administration & dosage* / Q000097:blood; D005260:Female; D006801:Humans; D007564:Japan; D018673:Nutrition Policy; D014481:United States
D001205:Ascorbic Acid