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Physiological interactions of lutein and β‐carotene in humans measured using 13C tracers and GC‐C‐IRMS

Our objective was to determine if coincident ingestion of lutein modifies the bioefficacy of β‐carotene in healthy women who ingest small tracer doses simulating those absorbed from dark green leafy vegetables. In a randomized crossover design, subjects (n = 7) ingested: (1) 1 mg of [13C]β‐carotene, and (2) 1 mg of [13C]β‐carotene plus 3 mg of [13C]lutein. Blood samples were collected at baseline and then hourly for 12 h; additional blood samples were drawn at 16, 24, 48, 72, 96, 192, 360, and 528 h. Plasma concentrations of [13C]β‐carotene, [13C]lutein, and [13C]retinol conversion products were measured by using gas chromatography–combustion interfaced–isotope ratio mass spectrometry (GC–C–IRMS). The 96‐h area under the plasma concentration versus time curve (AUC) for [13C]retinol was 16.8 ± 4.1 μmol·h/L and 16.6 ± 3.3 μmol·h/L after subjects ingested the individual dose of [13C]β‐carotene and the combined dose of [13C]β‐carotene plus [13C]lutein, respectively. Similarly, there was no significant difference between treatments in the 528‐h AUC for [13C]β‐carotene. We conclude that lutein does not affect the bioavailability or bioefficacy of β‐carotene when ingested in amounts and lutein:β‐carotene ratio characteristic of dietary dark green leafy vegetables. Thus lutein is unlikely to be the matrix component that accounts for the limited bioavailability in humans of β‐carotene in dark green leafy vegetables.