Effect of long-term administration of beta-carotene on lymphocyte subsets in humans.

To examine whether or not beta-carotene alters immune indexes, we performed a single-blind trial in healthy male nonsmokers. Lymphocyte subsets were assessed by double labeling with monoclonal antibodies before and after 44 wk of administration of either beta-carotene (60 mg/d; n = 10) or placebo (n = 10). In addition, we measured the beta-carotene concentrations in plasma, mononuclear cells (MNC), platelets, and red blood cells (RBCs), as well as the plasma alpha-tocopherol concentration. An increase of plasma and MNC beta-carotene concentrations to four and three times the baseline value was noted after 2 and 4 wk, respectively. The CD4-CD8 ratio increased after 9 mo of beta-carotene administration whereas natural killer cells, virgin T cells, memory T cells, and cytotoxic T cells remained unaltered throughout the study. No side effects or toxicities were detected by a questionnaire survey and routine laboratory tests.