Zinc

Zinc supports immune defence, wound healing, taste, smell and growth. It is one of the more clearly useful supplements when intake is low, and one of the easier ones to overdo — long-term high intake causes copper deficiency, which can cause anaemia and nerve problems.

Supplemental zinc is bound to different partner molecules. Acetate and gluconate are the forms used in most cold lozenge trials; oxide is poorly absorbed. Lozenges are designed to dissolve in the mouth rather than be swallowed.

Zinc is a structural and catalytic component of hundreds of enzymes and of proteins that regulate gene expression, which is why deficiency affects so many systems at once.

Correcting deficiency and treating childhood diarrhoea in high-prevalence settings are established. Zinc lozenges started early can shorten cold duration in several trials, though results vary by formulation. Zinc is part of an established eye-supplement combination studied in a large trial for intermediate macular degeneration. Claims of general immune enhancement in people with adequate status are not supported.

Laboratory work describes zinc-dependent enzymes, effects on viral replication and immune-cell function, and mechanisms of zinc-induced copper depletion.

Evidence gap: Non-human and in-vitro evidence. It supports mechanism and does not establish benefit in people with adequate zinc.

Zinc competes with copper and iron for absorption and binds certain antibiotics. Long-term high intake is the usual cause of copper deficiency seen clinically.

Short-term high doses cause nausea, metallic taste, stomach pain and vomiting; lozenges commonly cause taste disturbance and mouth irritation. Long-term intake above the upper limit causes copper deficiency with anaemia and potentially irreversible nerve damage, and can impair immune function — the opposite of what users intend. Intranasal zinc products have caused permanent loss of smell and should not be used. Denture creams containing zinc have also caused copper deficiency. Very high intake can reduce HDL cholesterol.

Tablets, capsules, syrups and lozenges are common; lozenge trials required dissolving in the mouth rather than swallowing.

Food sources cover needs for most people; plant-based eaters may need more because of phytate. Supplementation fits deficiency, guideline-based childhood diarrhoea management, early cold lozenge use, and clinician-supervised eye formulas. It does not replace treatment of infection or of skin disease.

Educational example: an adult takes a high-dose zinc immune supplement daily for two years and develops anaemia and tingling in the feet caused by copper deficiency. Decision factors are dose, duration, copper status and whether zinc was needed at all. Questions to ask: how much elemental zinc is this, how long should I take it, and should copper be monitored? Immune-boosting marketing rarely mentions that excess zinc suppresses immune function and depletes copper.