Beta-carotene's effects on serum lipoproteins and immunologic indices in humans.
 Doses of beta-carotene for cancer-prevention trials have been chosen based on epidemiologic data.
 Mechanisms of the putative antineoplastic effects by beta-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 beta-carotene/d for 1 mo in this randomized placebo-controlled, open-label, parallel study.
 Plasma beta-carotene concentrations were markedly increased by 2 wk and were correlated with dose.
 Beta-carotene concentrations plateaued between 2 and 4 wk except for the 300-mg group.
 Thus, we developed a dose-concentration curve to optimize beta-carotene-dose selection to achieve target plasma concentrations.
 We were unable to identify any effects of beta-carotene ingestion on the immunologic indices studied, but modest increases in high-density-lipoprotein cholesterol were observed in all beta-carotene-treated groups.
