Modulation of plasma all-trans retinoic acid concentrations by the consumption of carotenoid-rich vegetables

Objective A human intervention trial was conducted to determine the effects of consumption of carotenoid-rich vegetables on levels of retinol (ROL) and the active vitamin A metabolite all-trans retinoic acid (ATRA). Methods The study was divided into four periods, each lasting 2 wk: weeks 1–2, a low carotenoid period; weeks 3–4, daily consumption of 330 mL of tomato juice; weeks 5–6, 330 mL of carrot juice daily; and weeks 7–8, 10 g of dried spinach powder daily. ROL and ATRA concentrations were measured after each 2-wk study period. Results and conclusion This study shows that consumption of carrot juice containing high concentrations of the pro–vitamin A carotenoid β-carotene results in slightly, non-significantly increased plasma ROL concentrations and strong, significantly increased (almost double, from 1.2 ± 0.3 to 2.0 ± 0.31 ng/mL) plasma concentrations of ATRA, whereas consumption of tomato juice and spinach powder results in no significant alteration in concentrations of plasma ROL and ATRA.