Original research
β-Carotene and selenium supplementation enhances immune response in aged humans

https://doi.org/10.1016/S1096-2190(00)00009-3Get rights and content

Abstract

Background: Nutritional research has focused on the effects of specific nutrients' ability to cause or prevent cancer. While β-carotene and selenium (both important for antioxidant systems) have cancer prevention capabilities, their antineoplastic mechanism(s) remains to be elucidated. Methods: In a prospective, randomized study design we evaluated immunological changes in free-living, healthy aged humans (57–84 years of age) given a placebo, β-carotene (45 mg/day), and/or selenium (400 μg/day) supplement for 6 months and after 2 months of discontinuation. Peripheral blood lymphocytes were evaluated and subtyped using flowcytometry. Natural killer (NK) cell cytotoxicity was determined by a fluorescent method. Plasma diene conjugates were assessed to evaluate changes in oxidative stress. Results: Selenium and selenium plus β-carotene supplementation caused an increase in total T cells by 27% and 31%, respectively (p < .05). The only group that was different (in T lymphocytes) from the controls (placebo group) after 6 months of supplementation (p < .05) was the selenium-supplemented group (+65%). Much of this increase was the result of an increase in CD4+ T-cell subsets. Selenium or β-carotene supplementation for 3 months increased NK cell cytotoxicity over pretreatment levels by 58% and 34%, respectively; however, these levels returned to +12% and −6% of pretreatment levels after 6 months supplementation. Selenium plus β-carotene supplementation caused an increase in the percentage of NK cell by 121% and 161% at 3 and 6 months, respectively. However, the increased numbers of NK cells were not correlated with NK cell activity. Conclusions: We found that selenium enhanced immune function (NK cell cytotoxicity) and phenotypic expression of T-cell subsets, whereas β-carotene affected only immune function. Increased NK cell cytotoxicity may last for only a short period of supplementation and was not sustained throughout the 6 months of supplementation. Supplemental selenium and β-carotene seemed to affect immune function in aged subjects by different mechanisms.

Section snippets

Study Populations

Healthy, free-living aged adults (over 55 years of age) living in southern Arizona volunteered and signed an informed-consent form to participate in this study, which was approved by the University of Arizona Human Subjects Committee. Participants were screened to determine eligibility by obtaining medical histories and current nutrient supplementation practices as well as to assess subject's current physical well being. Participants taking high levels of nutrient supplements or having chronic

Participants' Characteristics

Participants' n = 45 characteristics are noted by supplementation group in Table 1. No classic symptoms of toxicity (hypercarotendermia for β-carotene or garlicky odor to the breath of those supplemented with selenium) were noted. All groups had pill consumption compliance of 90% or greater as determined by pill counts every month. There was a 22% overall attrition rate, therefore, subjects included in statistical analysis included: 8 in the placebo group, 8 in the selenium group, 12 in the

Discussion

Our results indicate that supplementation for 6 months with β-carotene and selenium in aged adults caused changes in lymphocyte populations and function. These changes may represent a portion of β-carotene's and selenium's effects on cancer and disease prevention. One of the most intriguing findings was the elevation in NK cell cytotoxicity after 3 months of selenium or β-carotene supplementation. However, after 6 months of supplementation NK cell activity returned to pretreatment levels. Upon

Acknowledgements

This research was supported by Wallace Genetic Foundation, Inc. and Phi Beta Psi Sorority.

We gratefully acknowledge and thank Barb Corilus for her expertise in flow cytometry and Dr. Andrea Arquitt for determining selenium concentrations.

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    Current address: Shokei-Gakuen University, Department of Domestic Sciences, Kumamoto, Japan.

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