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 14C-lutein (125 nmol, 36 nCi 14C), 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 14C first appeared in plasma 1 h after dosing and reached its highest level, approximately2.08% of dose/L plasma, at 14 h post-dose. The plasma pattern of 14C did not include a chylomicrons/VLDL (intestinal) peak like that when the same subject received 14C-beta-carotene (a previous test), suggesting that lutein was handled differently from beta-carotene by plasma lipoproteins. Lutein had an elimination half-life (t1/2) of approximately10 d. Forty-five percent of the dose of 14C 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.