Multivitamin
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C Mixed or limited evidenceVitamins & MineralsGeneral Health
Vitamins & Minerals
Zinc
Also known as: zinc gluconate, zinc picolinate, zinc acetate
Shortens colds if you start within a day and use lozenges — and does approximately nothing for testosterone unless you were deficient.
Grade BGood human evidence
Studied dose15-30 mg/day for maintenance; cold lozenges use a separate short-term protocol
TimingWith food
EvidenceGrade B
CategoryVitamins & Minerals
Deficiency correction and immune function are well established. Zinc lozenges started early shorten cold duration in meta-analyses, though trial quality varies. The testosterone claim holds only in deficiency.
Zinc has one genuinely useful acute application and a great deal of marketing built on top of it.
The useful part is colds, and the details are unusually strict. Meta-analyses of zinc lozenges find a meaningful reduction in cold duration — roughly a couple of days — but only when three conditions hold: the format is a lozenge that dissolves in the mouth, the dose is high (75-100 mg daily of elemental zinc), and dosing starts within about 24 hours of the first symptom. Swallowed capsules do not work, because the mechanism is local zinc contact with the throat rather than anything systemic. Start on day three and the window has closed. Trial quality in this literature is uneven and the effect size varies, which is why the grade is B rather than A.
Deficiency is the other real story. Zinc is essential, deficiency impairs immune function, wound healing, taste, and testosterone production, and it is common in vegetarians (phytates in grains and legumes bind zinc), older adults, and people with malabsorption. Correcting it fixes all of the above.
Which sets up the claim you see most often in fitness marketing. Yes, zinc deficiency lowers testosterone, and yes, correcting deficiency restores it. No, this does not mean zinc raises testosterone in men who are already replete — that is the same pattern as vitamin D, and the trials say the same thing. ZMA, the branded zinc-magnesium formula sold on exactly this claim, has failed to raise testosterone in trained athletes.
The caution worth knowing: chronic high-dose zinc induces copper deficiency by upregulating the intestinal protein that traps copper, and copper deficiency causes anaemia and neurological damage. That is why the tolerable upper limit sits at 40 mg daily for ongoing use. A week of high-dose lozenges during a cold is fine; taking 50 mg every day for a year is not. Take it with food, and keep maintenance doses modest.
How it works
Zinc is a structural and catalytic component of hundreds of enzymes and of the zinc-finger transcription factors that regulate gene expression, which is why deficiency hits fast-dividing tissue — immune cells, gut lining, skin — first. The cold effect appears to be local: zinc ions in the throat interfere with rhinovirus replication and adhesion, which is why lozenges work and swallowed capsules do not.
What the evidence supports
- Corrects deficiency — immunity, wound healing, taste clear-cut nutrient repletionA
- May shorten common cold duration some zinc acetate or gluconate lozenge trials show about 1-2 fewer days when started within 24 hours; results and products varyB
- Restores testosterone in deficient men repletion effect, not enhancementB
- Raises testosterone in replete men null in trained athletes; the basis for most ZMA marketingD
Safety
Safe at 15-30 mg/day. The main chronic risk is copper depletion above roughly 40 mg/day sustained, which causes anaemia and neuropathy. Acute high doses cause nausea and vomiting, especially on an empty stomach. Intranasal zinc products caused permanent loss of smell and were withdrawn — avoid them entirely.
Reported side effects
- Nausea, particularly without food
- Metallic taste and mouth irritation from lozenges
- Copper deficiency with sustained high doses
Interactions
- Reduces absorption of tetracycline and quinolone antibiotics — separate by 2-4 hours.
- Competes with copper and iron for absorption.
- Thiazide diuretics increase urinary zinc loss.
This guide is educational, not medical advice. Talk to a physician or pharmacist before starting any supplement, especially alongside prescription medication or a medical condition.
Common questions
- What does Zinc do?
- Shortens colds if you start within a day and use lozenges — and does approximately nothing for testosterone unless you were deficient. Its best-supported effects are corrects deficiency — immunity, wound healing, taste and may shorten common cold duration.
- Does Zinc actually work?
- Good human evidence (grade B). Deficiency correction and immune function are well established. Zinc lozenges started early shorten cold duration in meta-analyses, though trial quality varies. The testosterone claim holds only in deficiency.
- How much Zinc should I take?
- The studied range is 15-30 mg/day for maintenance; cold lozenges use a separate short-term protocol, daily with food; do not exceed 40 mg/day long term unless medically supervised. Start at the low end — more is not better once the effective range is covered.
- When should I take Zinc?
- With food — zinc on an empty stomach is a reliable route to nausea. For colds, zinc acetate or gluconate lozenges may modestly shorten symptoms when started within 24 hours; follow the product directions and use them for no more than about 1 week because the acute dose can exceed the chronic upper limit.
- Is Zinc safe?
- Safe at 15-30 mg/day. The main chronic risk is copper depletion above roughly 40 mg/day sustained, which causes anaemia and neuropathy. Acute high doses cause nausea and vomiting, especially on an empty stomach. Intranasal zinc products caused permanent loss of smell and were withdrawn — avoid them entirely. The most reported side effects are nausea, particularly without food, metallic taste and mouth irritation from lozenges, copper deficiency with sustained high doses.
- What should you not mix Zinc with?
- Reduces absorption of tetracycline and quinolone antibiotics — separate by 2-4 hours. Competes with copper and iron for absorption. Thiazide diuretics increase urinary zinc loss. Ask a pharmacist or physician before combining it with prescription medication.
References
Evidence review last updated