Vitamin A isotope dilution predicts liver stores in line with long-term vitamin A intake above the current Recommended Dietary Allowance for young adult women

Background: The Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for vitamin A are 1.7 and 2.4 μmol/d (500 and 700 μg retinol activity equivalents/d), respectively, for nonpregnant, nonlactating women aged ≥19 y. This intake is presumed to maintain a minimally acceptable liver concentration of 0.07 μmol (20 μg) retinol/g; however, liver reserves have not been evaluated with respect to vitamin A intake in women of any age group defined in the Dietary Reference Intakes. Objective: This cross-sectional study examined vitamin A intake and liver reserves estimated by stable-isotope dilution testing. Design: Forty nonpregnant, nonlactating women (mean ± SD age: 22.4 ± 2.3 y) completed a Harvard food-frequency questionnaire (FFQ) and 3-d diet record (3DDR) before undergoing vitamin A status assessment by using a [¹³C₂]retinol stable-isotope dilution test. Results: Vitamin A intake was 70% higher than the RDA by both dietary-assessment methods (P < 0.001). The mean (±SD) liver concentration of vitamin Awas 0.45 ± 0.31 μmol/g (129 ± 89 μg/g) and ranged from 0.09 (26 μg/g) to 1.79 μmol/g (513 μg/g). Liver and total-body vitamin A were highly correlated with intake measured by FFQ (P ≤ 0.009), but 3DDR was not (P ≥ 0.22). Prediction equations were developed for 3-and 7-d data. Conclusions: In this well-nourished population, vitamin A consumption was considerably higher than recommended, and liver reserves were consistent with intake. Because of their sensitivity, stable-isotope techniques can help to describe the vitamin A status and better characterize the intake needs of all groups defined in the Dietary Reference Intakes. Registration was not required for this trial.