INTESTINAL-ABSORPTION, SERUM CLEARANCE, AND INTERACTIONS BETWEEN LUTEIN AND BETA-CAROTENE WHEN ADMINISTERED TO HUMAN ADULTS IN SEPARATE OR COMBINED ORAL DOSES

Single equimolar doses (0.5 mu mol/kg body wt) of lutein and/or beta-c arotene in true solution in oil were given to eight adult subjects and 13 blood samples were taken during the subsequent 840 h. Whereas the mean serum concentration of lutein showed a single maximum at 16 h, th at of beta-carotene peaked at 6 h and then again at 32 h. Subsequently , lutein and beta-carotene were cleared at approximately the same rate from the serum. The mean (+/- SEM) areas under the curve (AUCs) for l utein and beta-carotene during the first 440 h differed significantly: 59.6 +/- 9.0 and 26.3 +/- 6.4 mu mol . h/L, respectively (P < 0.005). AUC values did not correlate with initial serum concentrations of the given carotenoid or with the order of dosing. When combined in the sa me dose, beta-carotene significantly reduced the serum AUC values for lutein to 54 - 61% of control values (P < 0.025), whereas lutein reduc ed the AUC value for beta-carotene in five subjects but enhanced it in three subjects. Effects of lutein on the AUC for beta-carotene were i nversely related to the AUC for beta-carotene alone. Thus, carotenoids clearly interact with each other during intestinal absorption, metabo lism, and serum clearance, although individual responses can differ ma rkedly.