Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2002
Publication Date: 3/25/2002
Citation: Pinna, K., Kelley, D.S., Taylor, P.C., King, J.C. 2002. IMMUNE FUNCTIONS ARE MAINTAINED IN HEALTHY MEN WITH LOW ZINC INTAKE. Journal of Nutrition. 132:2033-2036, 2002. Interpretive Summary: Zinc is critical for the development and maintenance of a healthy immune system. Severe zinc deficiency impairs several aspects of immune status, but the effects of moderate zinc deficiency on human immune status is not known. The purpose of this study was to characterize the effect of low zinc intake on clinical measures of immune response and to identify the initial defects that may result from zinc-restricted diets. Eight healthy men lived at the metabolic research unit and were fed diets of known nutrient composition. Zinc intake was 4.6 mg/d for the first and last five weeks, and 13.7 mg/d for the middle ten weeks of the study. Indices of immune status were examined in vivo and by using the blood samples collected at the end of each metabolic period. Subject remained healthy, and they did not show any signs of zinc deficiency during the period of restricted zinc intake. Plasma zinc concentration, and many indices (delayed hypersensitivity, number of circulating immune cells, cytokine and superoxide production) of immune response were not affected by the amount of zinc intake. In vitro lymphocyte proliferation and the production interleukin 2- receptor were decreased with zinc restriction, but these markers did not restore within five weeks of zinc repletion. These two responses may be the most sensitive to restricted zinc intake or these may have changed due to factors other than zinc intake. Future studies are needed to address this issue.
Technical Abstract: Although immunity is known to be impaired during severe zinc deficiency, there is limited information about the effects of mild zinc depletion on immune response in human subjects. We evaluated the effects of a zinc-restricted diet (4.6 mg/d) on several indices of immunity in 8 healthy men. The subjects consumed zinc supplements with 9.1 mg/d during the 5-wk baseline (BL) and 5-wk repletion (RP) periods, and placebos during the 10-wk zinc-restriction (ZR) period. Leukocyte numbers and functions were studied at the end of each metabolic period. Following ZR, there were significant reductions (P < 0.05) in the proliferation of peripheral blood mononuclear cells (PBMNC) stimulated with phytohemagglutinin (PHA: 1.25, 2.5, 5.0, 10.0, and 20.0 mg/L) and in the in vitro secretion of interleukin-2 receptor (PHA: 2.5 mg/L). These variables remained significantly reduced even after 5 wk of zinc repletion. The amount of zinc consumed did not alter the numbers of circulating neutrophils, monocytes, and lymphocytes, the in vitro PBMNC secretion of interferon-gamma and tumor necrosis factor-alpha, and neutrophil superoxide production. The results suggest that lymphocyte proliferation and IL-2R expression may be early markers of mild zinc deficiency.