Simplified approaches for estimating vitamin A stores and β-carotene bioconversion in humans (39.6)

Better methods are needed to assess vitamin A (VA) status and the efficiency of bioconversion of β-carotene (BC) to retinol (ROH). Data on plasma ROH kinetics from 2 h to 14 d after an oral tracer dose of [13C10]BC and [13C10]retinyl acetate (RAc) to 33 healthy young adults were analyzed using model-based compartmental analysis (WinSAAM, the Windows version of the Simulation, Analysis and Modeling software). The 6-compartment model that fit data for all subjects predicted 5.3 pools of plasma ROH were transferred into extravascular stores each day, with ~17%/d recycling back to plasma; 6.5%/day was irreversibly lost and total body VA stores (TBS) were 146 ± 89 μmol (mean ± SD). We derived a simplified isotope dilution (“Olson”) equation for TBS, eliminating several factors and assumptions: TBS = F * (1 / SA), where F (fraction of dose [FD] absorbed and retained) was estimated as 0.61 from the kinetic data and SA (specific activity) is FD 13C10[ROH] in plasma 3 d after dosing / plasma ROH pool (μmol). TBS c...