How it works
Zinc is required by hundreds of enzymes and is involved in immune cell function, wound healing, DNA and protein synthesis, taste and smell, and testosterone production. Small amounts are lost in sweat. Zinc from plant foods is less available because phytates in grains and legumes bind it, so vegetarians and vegans may have higher requirements. Zinc lozenges are thought to act locally in the throat against cold viruses.
What research supports
- Corrects low zinc intake or deficiency, supporting immune function and tissue repair
- Zinc lozenges started within 24 hours of cold symptoms may shorten cold duration in some studies
- Supports normal testosterone levels in people who are deficient; no clear effect in those with adequate zinc
- No clear evidence of performance benefits in well-nourished athletes
Dosage
Recommended intake for adults is 8 mg (women) to 11 mg (men) per day from all sources. Supplements commonly provide 8–25 mg. Cold studies used lozenges providing about 75 mg per day for short periods. The adult tolerable upper limit is 40 mg per day.
Timing
Zinc is best absorbed on an empty stomach, but taking it with food reduces nausea. Avoid taking it at the same time as iron or calcium supplements, which compete for absorption. For colds, lozenges are used every few hours, starting at first symptoms, for a few days only.
Side effects
- Nausea, stomach upset and metallic taste, especially on an empty stomach
- Long-term intake above 40 mg per day can cause copper deficiency, anaemia and reduced immune function
- Zinc nasal sprays have been linked to loss of smell and should be avoided
Cautions
- Separate zinc from certain antibiotics (quinolones, tetracyclines) and penicillamine by several hours
- Do not take high doses long term without medical guidance
- Some diuretics increase zinc loss
- Athletes subject to anti-doping rules should only use products certified by an independent third-party testing program for banned substances; certification lowers, but does not eliminate, the risk of contamination.
Food sources
Oysters, Beef and lamb, Crab and lobster, Pumpkin seeds, Chickpeas and lentils, Cashews, Dairy, Fortified cereals.