Kinetics of 14C distribution after tracer dose of 14C-lutein in an adult woman

Lutein is an oxygenated carotenoid (xanthophyll) found in dark green leafy vegetables. High intakes of lutein may lower the risk of age-related macular degeneration. Current understanding of human lutein metabolism as it might occur in vivo is incomplete. Therefore, we conducted a feasibility study where we dosed a normal adult woman with C-14-lutein (125 nmol, 36 nCi C-14), dissolved in olive oil (0.5 g/kg body weight) and mixed in a banana shake. Blood, urine, and feces collected before the dose was administered served to establish baseline values. Thereafter, blood was collected for 63 d following the dose, while feces and urine were collected for 2 wk post-dose. The 14C contents in plasma, urine, and feces were measured by accelerator MS. The C-14 first appeared in plasma 1 h after dosing and reached its highest level, approximate to 2.08% of dose/L plasma, at 14 h post-dose. The plasma pattern of 14 C did not include a chylomicrons/VLDL (intestinal) peak like that when the same subject received C-14-beta-carotene (a previous test), suggesting that lutein was handled differently from P-carotene by plasma lipoproteins. Lutein had an elimination half-life (t(1/2)) of approximate to 10 d. Forty-five percent of the dose of C-14 was eliminated in feces and 10% in urine in the first 2 d after dosing. Quantifying human lutein metabolism is a fertile area for future research.