Plasma appearance of labeled β-carotene, lutein, and retinol in humans after consumption of isotopically labeled kale

The bioavailability of carotenoids from kale was investigated by labeling nutrients in kale with ¹³C, feeding the kale to seven adult volunteers, and analyzing serial plasma samples for labeled lutein, β-carotene, and retinol. Ingested doses of labeled carotenoids were 34 micromol for β-carotene and 33 micromol for lutein. Peak plasma concentrations, areas under the plasma concentration-time curves (AUCs), and percentages of dose recovered at peak plasma concentrations were calculated. Average peak plasma concentrations were 0.38, 0.068, and 0.079 micromolar for [¹³C]lutein, [¹³C]β-carotene, and [¹³C]retinol, respectively. Average AUC values (over 28 days) were 42.8, 13.6, 13.2 micromolar h for [¹³C]lutein, [¹³C]β-carotene, and [¹³C]retinol, respectively. Percentages of dose recovered at peak plasma concentrations were 3.6, 0.7, and 0.7% for [¹³C]lutein, [¹³C]β-carotene, and [¹³C]retinol, respectively. A positive relationship was observed between baseline plasma retinol levels and [¹³C]retinol plasma response. It is possible that this relationship was mediated either through some aspect of β-carotene absorption or via the common pathways of metabolism for postdose and endogenous retinoid.