Zinc

•RCT evidence— AMD (AREDS2), common cold (Cochrane meta-analyses)

Why it matters

Zinc is a cofactor for over 300 enzymes including DNA repair (PARP, BRCA1 interaction), antioxidant defence (SOD), insulin storage, taste perception, and innate + adaptive immune function. Population deficiency is common in older adults due to reduced absorption and dietary changes.

Evidence-based uses

• AMD progression: zinc 80 mg + copper 2 mg (AREDS2 formula) slows progression of intermediate to advanced AMD.
• Common cold duration: zinc lozenges (especially acetate) within 24 hours of onset reduce duration by ~1.5 days.
• Acne: oral zinc moderate evidence; topical clearer.
• Wilson disease, sickle cell: clinical-indication use.

The copper trade-off

Chronic high-dose zinc (>40 mg/day) blocks copper absorption, causing sideroblastic anaemia and myelopathy in case reports. Long-term zinc supplements should include ~1–2 mg copper.

Cautions

• Interferes with absorption of iron, calcium, fluoroquinolone and tetracycline antibiotics.
• Intranasal zinc has caused permanent anosmia; do not use.
• High doses cause nausea and may suppress immunity (the opposite of desired effect).

Related entries

Age-related macular degeneration, Vitamin D, Magnesium.