There is substantial evidence to support an important role for zinc in immune processes. Adequate zinc status is essential for T-cell division, maturation and differentiation; lymphocyte response to mitogens; programmed cell death of lymphoid and myeloid origins; gene transcription; and biomembrane function. Lymphocytes are one of the types of cells activated by zinc. Zinc is the structural component of a wide variety of proteins, neuropeptides, hormone receptors and polynucleotides. Among the best known zinc-dependent hormones/enzymes are Cu, Zn superoxide dismutase, an enzyme component of the antioxidant defense system, and thymulin, which is essential for the formation of T-lymphocytes. In animals and humans, zinc deficiency results in rapid and marked atrophy of the thymus, impaired cell-mediated cutaneous sensitivity and lymphopenia. Primary and secondary antibody responses are reduced in zinc deficiency, particularly for those antigens that require T-cell help, such as those in heterologous red blood cells. In addition, antibody response and the generation of splenic cytotoxic T cells after immunization are reduced. ZINC ALSO INHIBITS THE PRODUCTION OF TUMOR NECROSIS FACTOR, which is implicated in the pathophysiology of cachexia and wasting in acquired immune deficiency syndrome.

Zinc supplements have been shown to inhibit about half the herpes family viruses in vitro, up to 97%. See: Arens M. et al. Zinc salts inactivate clinical isolates of herpes simplex virus in vitro. J Clinical Microbiology. 2000;38:1758-1762.

There was another review of seven double-blind studies that showed a reduction in symptoms and duration of colds. (I believe the dose was 23 mg every two hours while awake, around 200 mg per day. They stated that 13 mg was the minimum effective dose.) See: Marshall S. Zinc gluconate and the common cold. Review of randomized controlled trials. Can Fam Physician 1998 May;44:1037-42.

Additionally, many of us are deficient in zinc.

Only 55.6 percent of 29,000 people, including people who take zinc supplements or multis with zinc, consumed adequate zinc, which was defined as about 12 mg or more per day. (Not enough to fight disease, really.) See: Briefel RR, et al. Zinc intake of the U.S. population: findings from the Third National Health and Nutrition Examination Survey, 1998-1994. J Nutrition, 2000;130:1367S-1373S.