The effect of zinc and vitamin A supplementation on immune response in an older population

OBJECTIVE: To determine if either supplemental vitamin A, zinc, or both increases cell-mediated immune response in an older population. DESIGN: A double-blind, randomized, controlled trial of supplementation with vitamin A and zinc. SETTING: Casa Di Riposo Roma III, a public home for older people in Rome, Italy. SUBJECTS: The health and nutritional status of 178 residents were evaluated. One hundred thirty-six residents agreed to participate in the trial and were randomized into four treatment groups, and 118 of these residents completed the trial. INTERVENTION: The four treatments consisted of: (1) Vitamin A (800 mu g retinol palmitate); (2) Zinc (25 mg as zinc sulfate); (3) Vitamin A and Zinc (800 mu g retinol palmitate and 25 mg as zinc sulfate); (4) Placebo capsules containing starch. MAIN OUTCOME MEASUREMENTS: Immune tests - counts of leucocytes, lymphocytes, T-cell subsets, and lymphocyte proliferative response to mitogens - were measured before and after supplementation. RESULTS: Zinc increased the number of CD4+DR+ T-cells (P = .016) and cytotoxic T-lymphocytes (P = .005). Subjects treated with vitamin A experienced a reduction in the number of CD3+ T-cells (P = .012) and CD4+ T-cells (P = .012). CONCLUSIONS: These data indicate that zinc supplementation improved cell-mediated immune response, whereas vitamin A had a deleterious effect in this older population. Further research is needed to clarify the clinical significance of these findings.