Zinc
Essential mineral for immunity, healing, and hormones.
Evidence tier
Moderate
Research weight
Citations
21 verified / 21
Classification
Mineral
❝
What the evidence says. Graded moderate: lozenges started within a day modestly shorten colds and correcting deficiency clearly helps immunity, but trials are inconsistent, effect sizes are small, and prevention benefits are unproven. (Moderate evidence: Several controlled trials; effects real but modest or context-dependent.)
What is Zinc?
Zinc is a mineral used for immune function. NutriDex grades the human evidence as Moderate. Zinc is essential for immune cell function, protein synthesis, and wound healing. Zinc lozenges started within 24 hours can shorten the common cold by roughly a day. Deficiency impairs immunity and is common in older adults and vegetarians. Chronic high intake interferes with copper absorption, so megadosing is discouraged.
Purported Benefits
✓Immune function
✓Shorter colds
✓Wound healing
✓Skin & testosterone
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Common cold duration (lozenges, treatment)Acetate lozenges >75 mg/day started early shorten colds ~33-40%; the 2024 Cochrane review rates duration benefit only low-certainty (~2.4 days). | Moderate | ↑ benefit · moderate | 4 |
| Cold/respiratory infection preventionA 2021 meta-analysis suggested ~32% lower respiratory infection risk, but the 2024 Cochrane review found little or no preventive effect. | Mixed | ↔ mixed · small | 2 |
| Glycemic controlUmbrella and 32-trial meta-analyses show lowered fasting glucose, HbA1c and HOMA-IR, with the largest effects in diabetic subjects. | Moderate | ↑ benefit · moderate | 3 |
| Acne / inflammatory skinMeta-analysis of 25 studies found acne patients have lower serum zinc and that zinc reduces inflammatory papules; trials heterogeneous. | Preliminary | ↑ benefit · small | 1 |
| Childhood diarrhea (treatment)Cochrane (33 RCTs) shows zinc shortens acute diarrhea ~11h in children >6 months, largest in malnourished; no benefit under 6 months, raises vomiting. | Strong | ↑ benefit · moderate | 2 |
| Depression adjunctSmall meta-analyses show modest reduction in depressive scores when added to antidepressants, with larger effect in adults 40+. | Preliminary | ↑ benefit · small | 2 |
| AMD progression (with antioxidants)Cochrane (26 RCTs) found AREDS-type antioxidant+zinc probably slows progression to late AMD (OR 0.72); zinc not isolated from the formula. | Moderate | ↑ benefit · moderate | 1 |
Dosing & Compounds
Typical Dose
8–11 mg/day RDA; up to 40 mg upper limit. Lozenges (75mg+/day) only short-term for colds.
Active Compounds
Safety & Cautions
Safe within limits (adult upper limit ~40 mg/day). Sustained high intake blocks copper absorption and can cause copper deficiency — anaemia and, rarely, irreversible nerve damage (myeloneuropathy). High-dose lozenges cause nausea and taste disturbance and are for short-term cold use only. Nasal zinc has caused permanent loss of smell — avoid it. Educational only — always check with your doctor or pharmacist before combining Zinc with any medicine.
Zinc drug interactions
Known or theoretical interactions between Zinc and common medications — educational, not exhaustive. Always check with your doctor or pharmacist before combining Zinc with any medicine.
Caution
Quinolone / tetracycline antibiotics
Zinc reduces absorption of these antibiotics; take antibiotic 2 h before or 4–6 h after zinc.
Divalent zinc chelates with fluoroquinolones and tetracyclines, forming insoluble complexes. NIH ODS — Zinc
Key Studies ★ 21 studies
Cochrane review
Nault 2024 (Cochrane review)
✓ PubMed
Across 34 RCTs (8,526 participants), zinc had little or no effect on preventing colds but may reduce duration of an ongoing cold (~2.4 days, low certainty), with more non-serious adverse events (taste/GI).
Cochrane review
Imdad 2023 (Cochrane review)
✓ PubMed
In 96 RCTs (219,584 children 6 months-12 years), preventive zinc made little to no difference to all-cause mortality but likely reduced all-cause diarrhea incidence and slightly increased height, with more vomiting.
Meta-analysis
Daneshvar 2024 (umbrella meta-analysis)
✓ PubMed
Umbrella review of interventional meta-analyses found zinc supplementation significantly reduced fasting blood glucose, insulin, HOMA-IR, and HbA1c (p<0.001), supporting benefit in glycemic control.
Systematic review
Nazari 2023 (GRADE dose-response meta-analysis)
✓ PubMed
GRADE-assessed dose-response meta-analysis of RCTs found zinc supplementation improved cardiovascular risk factors, lowering total cholesterol, triglycerides, LDL, glucose, and inflammatory markers.
systematic review
Evans 2023 (Cochrane review)
✓ PubMed
In 26 RCTs (11,952 participants), AREDS-type antioxidant plus zinc supplementation probably slowed progression to late age-related macular degeneration (OR 0.72, 95% CI 0.58-0.90) and reduced neovascular AMD (OR 0.62) and moderate visual acuity loss (OR 0.77), moderate-certainty evidence.
meta-analysis
Tabatabaeizadeh 2023 (systematic review/meta-analysis of RCTs, Journal of Infection)
✓ PubMed
Meta-analysis of randomized controlled trials of zinc in COVID-19 patients found that zinc supplementation did not provide additional clinical benefit on mortality or disease outcomes, concluding larger RCTs are needed.
Systematic review
Hemila 2024 (Frontiers)
✓ Full text
Critique of the 2024 Cochrane review reports that in 7 RCTs, zinc acetate/gluconate lozenges delivering >75 mg/day elemental zinc shortened common cold duration by 33% (95% CI 21%-45%).
Meta-analysis
Milani 2024 (EAACI taskforce)
✓ PubMed
EAACI taskforce meta-analysis found zinc in children with pneumonia showed limited benefit (reduced hospital length of stay but not time to recovery); no nutritional intervention recommended for routine treatment of pediatric respiratory infections.
Meta-analysis
Tabatabaeizadeh 2023
✓ PubMed
Meta-analysis found zinc supplementation in COVID-19 patients associated with significantly lower mortality versus controls (pooled OR 0.57, 95% CI 0.43-0.77, P<0.001).
Meta-analysis
Hunter 2021 (RCT meta-analysis, BMJ Open)
✓ PubMed
Meta-analysis of 28 RCTs (5,446 adults) found zinc modestly prevented respiratory infections (~32% lower risk) and shortened symptom duration by ~2 days, with more non-serious adverse events.
Systematic review
da Silva 2021 (systematic review/meta-analysis, Nutrition Reviews)
✓ PubMed
Meta-analysis of 5 RCTs found zinc added to antidepressant therapy modestly reduced depressive symptom scores (SMD -0.36; 95% CI -0.67 to -0.04), with larger effect in adults aged 40+.
Systematic review
Yee 2020 (systematic review/meta-analysis, Dermatologic Therapy)
✓ Source
Meta-analysis of 25 studies (12 RCTs; 2,445 participants) found acne patients had lower serum zinc and that zinc treatment significantly reduced inflammatory papule counts versus no zinc.
systematic review
Carducci 2021 (Cochrane review)
✓ PubMed
Across 25 RCTs (>18,000 women/infants), antenatal zinc supplementation made little or no difference to preterm birth (RR 0.87, 95% CI 0.74-1.03), low birthweight (RR 0.94), or small-for-gestational-age, providing insufficient evidence of benefit for maternal or neonatal outcomes.
Meta-analysis
Hemilä (Yosaee 2020) — Zinc in depression dose-response meta-analysis
✓ PubMed
Pooled RCTs: zinc supplementation significantly lowered depressive symptom scores in depressed patients (WMD -4.15 points; 95% CI -6.56 to -1.75), with benefit largely confined to zinc monotherapy; cohort data showed highest vs lowest zinc intake associated with 28% lower depression risk (RR 0.66, 95% CI 0.50-0.82).
Meta-analysis
Hemilä 2017 meta-analysis
✓ Source
Zinc acetate lozenges shortened colds ~33%.
Meta-analysis
Wang 2019 — Zinc supplementation and glycemic control meta-analysis
✓ PubMed
32 placebo-controlled trials (n=1700): zinc lowered fasting glucose (WMD -14.15 mg/dL; 95% CI -17.36 to -10.93), 2-h postprandial glucose (-36.85 mg/dL), HbA1c (-0.55%; 95% CI -0.84 to -0.27), HOMA-IR (-0.73), and hs-CRP (-1.31 mg/L); largest fasting-glucose effect in diabetic subjects and with inorganic zinc.
Meta-analysis
Hemilä 2017 — Zinc acetate lozenges, common cold IPD meta-analysis
✓ PubMed
Individual-patient-data pooling of 3 RCTs (199 patients, 80-92 mg/day elemental zinc as acetate lozenges): recovery rate ratio 3.1 (95% CI 2.1-4.7); by day 5, 70% of zinc vs 27% of placebo patients had recovered (NNT 2.3); no serious adverse effects.
Systematic review
Lazzerini 2016 — Oral zinc for treating diarrhoea in children (Cochrane)
✓ PubMed
33 RCTs, 10,841 children: in children >6 months, zinc shortened acute diarrhoea duration by ~11 h (MD -11.46 h; 95% CI -19.72 to -3.19) and reduced diarrhoea persisting to day 7 (RR 0.73; 95% CI 0.61-0.88); effect largest in malnourished children (~1 day). No benefit under 6 months; zinc increased vomiting risk (RR 1.57).
Meta-analysis
Hemilä 2017 — Zinc acetate vs gluconate lozenges, dose meta-analysis
✓ PubMed
Across randomized trials, zinc acetate lozenges shortened cold duration by ~40%; zinc lozenges delivering >75 mg/day elemental zinc reduced duration, whereas lower doses did not, indicating a dose threshold for efficacy.
Cochrane review
Cochrane 2013
✓ PubMed
Reduced cold duration when started early.
Study
Prasad 2008
✓ Full text
Supplementation improved immune markers in older adults.