Effects of β-carotene and selenium supplementation in aged humans.

Abstract

Aging is progressive deterioration of biological functions causing increased susceptibility to disease. This increased risk of disease is associated with a concomitant decrease in immune "responsiveness." Antioxidants are a group of compounds that prevent oxidative damage and disease. Researchers have focused on anti-oxidizing factors in disease prevention; however, nutrients which prevent oxidative damage may also have immunomodulating properties. βeta-carotene (BC), an antioxidant, has been shown to prevent cancer; while selenium, a key component of glutathione peroxidase, has shown promise in disease and cancer prevention. The objective was to determine if supplemental BC and selenium could enhance the immune response in elderly individuals. We investigated the functional responsiveness of lymphocytes that had been incubated with various concentrations of β-carotene and/or selenium. β-carotene enhanced natural killer (NK) cytotoxicity while selenium caused an immuno-suppressive effect. Interleukin-6 (IL-6) (a major factor in the acute phase immune response and B-cell differentiation) and IL-8 (a chemotactic factor) production was evaluated after short-term incubation with β-carotene or selenium. Selenium (0. 16 μg/ml) enhanced IL-6 production by 46 percent (P < 0.05) while the other concentrations of selenium or β-carotene did not significantly enhance IL-6 or IL-8 production. To further investigate selenium's and β-carotene's immunological effects, healthy elderly people (at least 60 years of age), were supplemented with high levels of BC and selenium. Participants were randomly assigned to receive a daily placebo, 45 mg β-carotene, 400 μg selenium, or 45 mg β-carotene plus 400 μg selenium for six months. NK cell activity and lymphocyte subpopulations were compared to pretreatment levels. Selenium and β-carotene supplementation for three months caused a statistically significant increase of 59% and 32% for NK cell activity respectively. At six months, NK cell activity returned to pretreatment levels. Selenium supplementation caused an increase in total T cells and CD4⁺ T cells. Selenium plus β-carotene supplementation increased the population of NK cells whereas β-carotene had little effect on phenotypic expression of lymphocytes. In conclusion, supplemental selenium and β-carotene enhanced immune function in healthy aged participants and their immunolomodulatory effects may partially explain their disease preventive properties.