Zinc

• Acute diarrhea (children): Strong evidence from multiple meta-analyses shows zinc supplementation reduces duration and stool volume in acute diarrheal illness, especially in populations with marginal zinc status. • Common cold: Meta-analyses suggest zinc acetate/gluconate lozenges started within 24 hours may shorten cold duration and reduce symptom severity; evidence is moderate and depends on formulation/dose. • Age-related macular degeneration (AMD): Large RCTs (AREDS/AREDS2) indicate zinc (with antioxidants and copper) slows progression of intermediate-to-advanced AMD; evidence is strong for progression risk reduction, not for primary prevention. • Wound healing: Evidence indicates zinc deficiency impairs healing; correcting deficiency and certain topical zinc preparations may aid healing; oral supplementation beyond repletion shows mixed-to-moderate evidence. • Taste/smell and immune support in deficiency: Zinc repletion improves dysgeusia and immune function when deficiency is present; evidence moderate. • Growth/development in malnourished children: Supplementation improves linear growth and reduces infections in zinc-deficient settings; evidence strong in low-resource populations.

Common: nausea, abdominal cramps, vomiting, diarrhea, metallic taste, heartburn—more likely on an empty stomach or at doses ≥40 mg/day. Lozenges: mouth/throat irritation, bad taste, nausea. Less common: headache, dizziness, drowsiness. Dose-related effects with long-term high intake (generally ≥50 mg/day for weeks–months): copper deficiency (anemia, neutropenia), impaired immune function, decreased HDL cholesterol, possible neurologic symptoms (paresthesias/ataxia) secondary to copper deficiency. Rare but serious: permanent loss of smell (anosmia) from intranasal zinc products—avoid intranasal forms. Hypersensitivity reactions are rare.

Typical supplemental doses: 5–25 mg elemental zinc/day for general supplementation; RDAs: adults—11 mg/day (men), 8 mg/day (women), with higher needs in pregnancy/lactation; Tolerable Upper Intake Level (UL): 40 mg/day for adults (lower for children). Cold treatment trials: lozenges providing ≥75–100 mg/day elemental zinc (often acetate or gluconate) divided over the day for ≤7–14 days; efficacy depends on adequate ionic zinc release and early initiation. Pediatric acute diarrhea: 10–20 mg/day for 10–14 days (per WHO/UNICEF guidance in low-resource settings). AMD (AREDS): 80 mg/day zinc oxide plus copper (to prevent deficiency) with antioxidants; used under ophthalmologist guidance. Formulations include zinc gluconate, acetate, sulfate, and picolinate; absorption can be reduced by phytates and concurrent iron/calcium/magnesium. Optimal dosing varies by individual status and indication; long-term high-dose use warrants copper monitoring.

• Known allergy to zinc or product excipients. • Existing copper deficiency or conditions at risk for copper deficiency—avoid high-dose zinc without medical supervision. • Concomitant use of interacting drugs where separation is not feasible (e.g., penicillamine for Wilson’s disease)—requires clinician guidance. • Pregnancy/lactation: Generally safe within RDA; avoid chronic high-dose supplementation unless prescribed. • Prostate health: Observational data link long-term high-dose supplemental zinc (>100 mg/day) with higher risk of advanced prostate cancer; avoid chronic high-dose use. • Kidney/liver impairment: Trace element homeostasis may be altered—use caution and medical oversight. • Surgery: No specific bleeding risk; disclose use. Avoid high-dose lozenges perioperatively due to nausea/aspiration risk. • Anticoagulation: Zinc does not appear to increase bleeding, but disclose to clinicians.