Zinc is an essential trace mineral required for metabolism, DNA synthesis, wound healing, and immune function. The body has no major storage system for zinc; regular dietary intake is necessary.
The Basics: What is Zinc & Where Do We Get It?
Good sources of zinc include meat, seafood, dairy, legumes, nuts, and whole grains. Most people in high-income countries obtain sufficient zinc from their diet.
When Zinc Levels Are Low
- Severe zinc deficiency is rare in high-income countries, but mild deficiency may affect approximately three in ten Australians.
- Low zinc levels can increase susceptibility to infections and slow recovery.
- Other effects include hair loss, poor wound healing, changes in taste and smell, skin problems, and in children, impaired growth and development.
- Immune dysfunction can occur with both too little and too much zinc.
Zinc and the Common Cold
A 2024 Cochrane review (34 studies) found that zinc supplements are unlikely to prevent colds but may reduce duration by about two days compared to placebo. The effect on symptom severity was unclear.
Zinc and Immune Health
Supplementation in zinc-deficient individuals can restore immune responses and reduce inflammatory markers. However, in people with adequate zinc levels, additional supplementation does not enhance immune function and may suppress immunity.
Zinc and Male Fertility
- Some studies have shown lower zinc levels in seminal fluid of infertile men.
- Older studies suggested possible improvements in sperm quality with supplementation.
- A 2020 large randomized controlled trial (over 2,000 couples) found that daily zinc (30 mg) plus folic acid (5 mg) for six months did not improve live birth rates or semen quality compared to placebo.
Supplement Forms and Interactions
- Zinc supplements come in various forms (e.g., amino acid chelate, gluconate) affecting absorption and tolerability.
- Zinc can interact with certain antibiotics (e.g., doxycycline, ciprofloxacin) and diuretics (e.g., hydrochlorothiazide), affecting drug absorption or mineral balance.
The Risks of Getting Too Much Zinc
- Recommended dietary intake: approximately 8 mg/day for women, 14 mg/day for men.
- Long-term high intake can interfere with copper absorption, leading to copper deficiency (anemia, nerve problems, weakened immunity).
- Short-term side effects: nausea, abdominal pain, vomiting, metallic taste.
- Upper safe limit for adults: 40 mg elemental zinc per day from all sources unless medically supervised.
The Bottom Line
- For most people eating a balanced diet, zinc supplements are unlikely to prevent colds, boost immunity, or enhance fertility.
- Zinc can be helpful for confirmed deficiency or conditions that reduce nutrient absorption.
- Zinc lozenges may modestly shorten cold duration if taken early, but benefits are inconsistent and side effects common.
- Individuals considering zinc supplements should consult a healthcare professional.