Zinc

What it is

Zinc is a trace mineral found in meat, shellfish, dairy, eggs, nuts, seeds and wholegrains. Your body needs it for immune cells, wound healing, taste and smell, DNA making and normal hormone function.

People take zinc for colds, skin problems such as acne, hair, immune support and, in men, testosterone. Vegetarians and vegans, older adults and people with some gut conditions can have lower intakes.

It is one of the supplements where more is not better. The gap between a useful dose and a problematic one is smaller than people expect.

How it works

Zinc is a component of hundreds of enzymes and proteins, including those that regulate gene activity and immune cell development. In colds, lozenges may work locally in the throat by interfering with viral replication or inflammation, though the exact mechanism is debated.

What the evidence says

• Strong Correcting low zinc
  If you are low, supplements restore levels; healthy people on a normal diet gain little.
• Moderate Shortening common colds (lozenges or syrup)
  Some reviews find a modest reduction in duration if started early, but products and doses vary widely and effects are not guaranteed.
• Limited Acne
  Some trials show improvement, but it is generally less effective than standard treatments and can upset the stomach.
• Limited Wound healing
  Helps when levels are low; little evidence of benefit when they are normal.
• Limited Testosterone in men
  Supplements raise testosterone mainly in men who are zinc-deficient, not in men with normal levels.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Many supplements contain 15-30 mg. UK guidance suggests that long-term supplemental intakes above about 25 mg a day should be avoided; check current guidance.
• Lozenges for colds typically give 13-25 mg per lozenge, used several times a day for a short spell only.
• Take with a meal if you get nausea.
• Do not take high doses for months without a reason; consider short courses.

Forms and what to look for

• Zinc bisglycinate (chelate) and picolinate: often better tolerated; evidence that they are far better absorbed is modest.
• Gluconate and acetate: common in lozenges and have the most cold research.
• Citrate: decent absorption and a mild taste.
• Sulphate: cheap but harsher on the stomach.
• Oxide: poorly absorbed; best avoided for supplements.

What to expect, and when

• If you were deficient, expect improvement over several weeks.
• For colds, if it works at all, the benefit is a day or so shorter illness.
• For skin or hair, it is usually slow and subtle and may show nothing.

Side effects

• Nausea, especially on an empty stomach
• Metallic taste
• Stomach pain or diarrhoea
• Long-term high doses can cause copper deficiency, with anaemia and nerve problems
• Nasal zinc products have been linked to permanent loss of smell, so avoid them

Interactions

• Reduces absorption of quinolone and tetracycline antibiotics; separate by several hours
• Competes with copper, and iron and calcium at high doses
• Can interfere with absorption of penicillamine
• Thiazide diuretics can increase zinc loss

Who should avoid it

• Anyone on long-term high-dose zinc without monitoring
• People with kidney disease without medical advice
• Pregnancy: stick to guidance on prenatal doses
• Anyone using nasal zinc products

Risks and safety

• Chronic intake over about 40 mg a day (the US upper limit) risks copper deficiency.
• Zinc is not on the WADA prohibited list.
• Zinc-containing denture creams used heavily have also caused zinc toxicity.
• Acute high doses cause vomiting and stomach pain.

Buying well: quality and testing

• Check the elemental zinc per serving; compound weight is bigger.
• Look for third-party testing such as NSF or USP.
• Multivitamins plus a separate zinc pill can quietly add up.
• Avoid formulas that promise testosterone boosts from zinc alone.

Bottom line

Zinc is worth considering if your diet is low in it or you are in a risk group, and a short course of lozenges at cold onset is a reasonable gamble. Long-term high doses are not harmless; keep to modest doses and take breaks.