Effect of beta-carotene on lymphocyte subpopulations in elderly humans: evidence for a dose-response relationship.

The effects of various doses (0, 15, 30, 45, and 60 mg/d) of supplementary beta-carotene were evaluated. The percentage of lymphoid cells with surface markers for T-helper and natural killer (NK) cells and cells with interleukin 2 (IL-2) and transferrin receptors were significantly and substantially increased in peripheral blood mononuclear cells collected from older human adult volunteers after supplementation with greater than or equal to 30 mg beta-carotene/d for 2 mo. The increase in the percentage of cells with markers of NK cells and in expression of IL-2 receptors was dose dependent. The plasma concentrations of beta-carotene were also elevated significantly; however, there was no increase in the amount of retinol present in plasma. This indicated that immunomodulation induced by beta-carotene may be due to the carotenoid rather than to an increased amount, and hence actions, of vitamin A. These results support the role of immunostimulation as a potential mechanism of action of beta-carotene with cancer-prevention potential.