Population-based plasma kinetics of an oral dose of [²H₄]retinyl acetate among preschool-aged, Peruvian children

Background: The deuterated-retinol-dilution technique provides a quantitative estimate of total-body vitamin A (TBVA) stores in adults. To apply the technique to children, information on plasma retinol kinetics in this age group is needed. Objectives: We described the plasma retinol kinetics of an oral dose of [²H₄]retinyl acetate in a population of Peruvian children (12-24 mo of age) in order to examine the relation between TBVA stores and individual plasma isotopic ratios 3 d after the dose and to estimate 1) the time required for the isotope dose to mix with endogenous vitamin A, 2) the fractional catabolic rate for retinol, and 3) TBVA stores. Design: An oral dose of [²H₄]retinyl acetate (14 μmol retinol equivalents) was administered to children (n = 107) to construct a population-level kinetic curve of the plasma ratio of [²H₄]retinol to retinol to estimate equilibration time and the fractional catabolic rate. TBVA stores were estimated by using a modification of the isotope dilution equation for adults. Results: The dose of [²H₄]retinyl acetate fully mixed with endogenous vitamin A 8 d after the dose. The fractional catabolic rate was 0.022/d (95% CI: 0.014, 0.030/d). Mean (± SD) TBVA stores were estimated as 0.097 ± 0.081 mmol (range: 0.016-0.392 mmol). Plasma ratios of [²H₄]retinol to retinol 3 d after the dose were correlated with the inverse of estimated TBVA stores (r = -0.74, P < 0.0001). Conclusions: Compared with previous results in adults, the equilibration time occurred earlier and the estimated system fractional catabolic rate was higher in this population of children. The modified isotope dilution equation provided estimates of hepatic vitamin A concentration that are similar to values reported in US children at autopsy.