Zinc

Zinc is an essential trace mineral required for the catalytic activity of hundreds of enzymes and for cellular processes including protein and DNA synthesis, wound healing, immune function, cell division, and the perception of taste.¹ The total zinc content of the adult body is approximately 1.5 grams in women and 2.5 grams in men, with most stored in skeletal muscle and bone.¹ Zinc is not stored in a freely accessible reserve, so a regular dietary intake is required to maintain status.

Several forms of zinc are used in dietary supplements, including zinc picolinate, zinc gluconate, zinc citrate, zinc sulfate, zinc acetate, and zinc bisglycinate. NIH ODS reports that absorption from supplements containing zinc citrate or zinc gluconate is similar at approximately 61% in young adults, and from zinc oxide is approximately 50%, but that head-to-head comparisons of all common supplemental forms are limited.¹ In all cases, the supplement label states the elemental zinc content, not the total weight of the zinc-containing compound.

Zinc is essential for normal immune function, and adequate zinc status is required for the development and function of cells involved in both innate and adaptive immunity.¹ Zinc supplementation is used to treat clinically diagnosed zinc deficiency, which is uncommon in developed countries but does occur in certain populations including individuals with malabsorptive disorders, chronic diarrhea, alcohol use disorder, sickle cell disease, and vegetarian or vegan diets that are high in phytate-containing foods (which bind zinc and inhibit absorption).¹

Zinc lozenges have been studied for the treatment of the common cold; meta-analyses suggest that zinc lozenges (specifically zinc acetate or zinc gluconate lozenges providing approximately 75 mg of elemental zinc per day, divided into multiple doses and started within 24 hours of symptom onset) may modestly shorten the duration of common cold symptoms. The evidence is inconsistent across trials, partly reflecting differences in zinc form, dose, and lozenge formulation.¹

Zinc is one component of the Age-Related Eye Disease Study (AREDS) and AREDS2 formulations, which were shown in large randomized trials to reduce the risk of progression to advanced age-related macular degeneration in individuals with intermediate AMD or advanced AMD in one eye.¹

Zinc supplementation has also been studied for wound healing, acne, and several other applications; the strength of evidence varies by application, and zinc supplementation in individuals who are not deficient does not consistently demonstrate benefit beyond what is achieved by adequate dietary intake.¹

Recommended Dietary Allowances for adults:¹

• Men 19 years and older: 11 mg/day
• Women 19 years and older: 8 mg/day
• Pregnancy: 11 mg/day (12 mg for adolescents)
• Lactation: 12 mg/day (13 mg for adolescents)

The Tolerable Upper Intake Level for adults is 40 mg/day from all sources combined.¹ Doses above this level should not be sustained without medical oversight because of the risk of copper deficiency and other adverse effects.

For specific applications, higher short-term doses are sometimes used: AREDS-style supplementation provides 80 mg of zinc per day (typically with 2 mg of copper to offset copper depletion); zinc lozenges for cold treatment provide approximately 75 mg of elemental zinc per day in divided doses but are typically used only for the duration of a cold.¹

Oral, as tablets, capsules, lozenges (for cold treatment), or as part of multivitamin/mineral products. Zinc oxide is also widely used topically (in diaper rash creams, sunscreens, and other skin products) — topical use does not contribute meaningfully to systemic zinc status.

Standard storage in a cool, dry place. No refrigeration required.

Several common interactions and considerations:¹

• Copper deficiency: Long-term zinc supplementation at doses above the UL (40 mg/day) can induce copper deficiency by interfering with copper absorption. This is the basis for the copper supplementation paired with high-dose zinc in AREDS2 formulations. Symptoms of copper deficiency include anemia and neurological changes; this is the most clinically significant consequence of chronic over-supplementation.
• Iron absorption: High-dose zinc (≥25 mg) taken at the same time as iron supplements can reduce iron absorption, and vice versa. Spacing zinc and iron supplements is recommended.
• Antibiotic interactions: Zinc can reduce absorption of certain antibiotics, including quinolones (such as ciprofloxacin) and tetracyclines. Doses should be separated by at least 2 hours.
• Penicillamine: Zinc reduces the absorption and effectiveness of penicillamine; clinically important in individuals being treated for Wilson disease or rheumatoid arthritis.
• Thiazide diuretics: Long-term thiazide use can increase urinary zinc excretion and may modestly reduce zinc status.

Acute high-dose oral zinc can cause nausea, vomiting, abdominal cramps, diarrhea, and metallic taste. Long-term excessive zinc intake has been associated with copper deficiency, immune dysfunction, and reduced HDL cholesterol levels.¹

Use of intranasal zinc products for cold treatment has been associated with cases of permanent loss of smell (anosmia) and is not recommended; this concern applies specifically to nasal gel and spray products, not to oral lozenges.¹