Beta-carotene's effects on serum lipoproteins and immunologic indices in humans

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Abstract
Doses of β-carotene for cancer-prevention trials have been chosen based on epidemiologic data. Mechanisms of the putative antineoplastic effects by β-carotene are unknown but may involve modulation of the immune system. We measured plasma carotenoid concentrations and selected immunologic indices at baseline and at 2 and 4 wk in 50 healthy humans (5 groups of 10 each) ingesting 0, 15, 45, 180, or 300 mg β-carotene/d for 1 mo in this randomized placebo-controlled, open-label, parallel study. Plasma β-carotene concentrations were markedly increased by 2 wk and were correlated with dose. Betacarotene concentrations plateaued between 2 and 4 wk except for the 300-mg group. Thus, we developed a dose-concentration curve to optimize β-carotene-dose selection to achieve target plasma concentrations. We were unable to identify any effects of β-carotene ingestion on the immunologic indices studied, but modest increases in high-density-lipoprotein cholesterol were observed in all β-carotene-treated groups.