Outcome
    Moderate Evidence

    Zinc for Immune Function

    Zinc has a well-defined role in immune function and deficiency clearly impairs it. For the common cold, lozenges started within 24 hours modestly shorten duration, but broader immune benefit in replete adults is unproven.

    Overview

    Zinc has a well-defined role in immune function and deficiency clearly impairs it. For the common cold, lozenges started within 24 hours modestly shorten duration, but broader immune benefit in replete adults is unproven.

    Verdict

    Mixed evidence

    How It Works

    Zinc is required for the development and function of neutrophils, natural killer cells and T lymphocytes; thymic atrophy and reduced T cell output are classic features of deficiency. It is also a cofactor for thymulin, the thymic hormone that drives T cell maturation. For the common cold specifically, the proposed mechanism is local rather than systemic: ionic zinc released in the oropharynx appears to interfere with rhinovirus binding to ICAM-1 and with viral replication. This is why lozenge formulation and dosing frequency matter more than total daily intake for that indication.

    Dosing & Protocol

    Typical dose

    Recommended dose
    8-11 mg/day meets requirements; therapeutic use is 75-100 mg/day of lozenges for up to 7 days during a cold
    Expected timeframe
    8-12 weeks

    Protocol

    form
    Zinc gluconate, sulfate or picolinate with food for status correction; zinc acetate lozenges at 75-100 mg/day only for acute cold treatment over 7 days
    duration
    8-12 weeks for deficiency correction, then return to dietary intake
    co factor
    Take with food and separate from iron, calcium and tetracycline or quinolone antibiotics by two hours. Evidence is mixed and depends entirely on baseline status. Zinc is required for thymic function, T cell maturation, B cell development, natural killer cell activity and neutrophil chemotaxis, and deficiency causes thymic atrophy and lymphopenia. Correcting deficiency restores these functions and reduces infection, demonstrated well in older adults and in low-income settings. In zinc-replete people, supplementation adds nothing, and excess suppresses lymphocyte function.
    titration
    Do not exceed 40 mg/day as an ongoing intake - above this zinc suppresses immune function rather than supporting it
    starting dose
    8 mg/day for women and 11 mg/day for men meets requirements; deficiency correction uses 15-30 mg/day of elemental zinc for a limited period

    Evidence

    What the studies say

    Cochrane and subsequent meta-analyses of zinc lozenges for the common cold find a reduction in symptom duration of roughly one day when high-dose zinc acetate or gluconate lozenges are started within 24 hours of onset. Prophylactic zinc reduces cold incidence in children in some trials, particularly in populations with prevalent deficiency. Evidence in well-nourished adults for general immune enhancement is weak, and results vary substantially with formulation, since zinc bound to citrate or mannitol releases little free ionic zinc. Lozenges commonly cause bad taste and nausea, and long-term intake above 40mg daily risks copper deficiency and can paradoxically impair immune function.

    Oral zinc for treating diarrhoea in children

    Score: 10/10
    2016
    systematic_review
    n=10841

    Lazzerini M, Wanzira H

    Zinc supplementation shortens acute diarrhoea in children over six months in settings at high risk of zinc deficiency.

    View source

    Effect of High-Dose Zinc and Ascorbic Acid Supplementation vs Usual Care on Symptom Length and Reduction Among Ambulatory Patients With SARS-CoV-2 Infection: The COVID A to Z Randomized Clinical Trial

    Score: 8/10
    2021
    rct
    n=214

    Thomas S, Patel D, Bittel B +5 more

    The study was stopped for a low conditional power for benefit with no significant difference among the 4 groups for the primary end point.

    View source

    Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials

    Score: 9/10
    2012
    meta_analysis
    n=2121

    Science M, Johnstone J, Roth DE +2 more

    Compared with patients given placebo, those receiving zinc had a shorter duration of cold symptoms (mean difference -1.65 days, 95% CI -2.50 to -0.81).

    View source

    Zinc for the common cold

    Score: 8/10
    2013
    systematic_review
    n=1387

    Singh M, Das RR

    Zinc started within 24 hours of onset shortened cold duration by about one day.

    View source

    Safety

    Caveats

    Benefit is limited to shortening cold duration in adults; children show no significant effect and a high-dose zinc trial in ambulatory viral infection was null.

    Less likely to help if

    People with adequate zinc status, which is most people eating a varied diet.

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    Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.