Judging by the claims on the bottles, it’s easy to assume a simple zinc tablet is a quick fix for everything from the common cold to low immunity and even male fertility.
But do they actually work? And should you be taking them?
What is zinc? Why does the body need it?
Zinc is an essential trace mineral required for hundreds of enzymes involved in metabolism, DNA synthesis, wound healing and immune function.
Within the immune system, zinc helps immune cells develop, communicate and respond to infection.
Because the body has no major storage system for zinc, we need to consume it regularly via food. Good dietary sources include meat, seafood (especially oysters), dairy products, legumes, nuts and wholegrains
Most people in high-income countries get enough zinc from their diet, particularly those who eat meat and animal products.
What happens when you don’t get enough zinc?
Severe zinc deficiency is uncommon in high-income countries, but around three in ten Australians are at risk of mild deficiency because they’re not getting enough zinc in their diet.
Zinc is essential for normal immune system function. It supports both innate immunity (the body’s immediate response to infection) and adaptive immunity (longer-term immune memory and antibody production).
When zinc levels are too low, people may be more susceptible to infections and slower to recover from illness.
Deficiency can also lead to hair loss, poor wound healing, changes in taste and smell, and skin problems.
In children, it can affect growth and development.
Importantly, immune dysfunction can occur at both ends of the spectrum: too little zinc and too much zinc can both impair immune responses.
Zinc and the common cold
Zinc is perhaps best known for its reputation as a “cold fighter”.
A 2024 Cochrane review (the gold standard for evidence-based research) investigated the role of zinc in preventing and treating the common cold. The review included 34 studies, 15 focusing on cold prevention and 19 on treatment.
Overall, it found zinc supplements are unlikely to prevent colds. But they might reduce their duration by about two days compared to placebo.
It was unclear if zinc affected the severity of cold symptoms, which are often the most annoying part about having a cold.
Zinc and immune health
Supplementation in zinc-deficient people can restore immune responses and reduce inflammatory markers. These benefits are largely confined to people who are zinc-deficient.
In people with adequate zinc levels, additional supplementation does not appear to enhance immune function.
In fact, excessive zinc intake can suppress immunity.
In other words, zinc helps the immune system work properly when it is lacking, but does not “boost” it beyond normal function.
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Zinc and male fertility
Zinc is often marketed to men as a fertility booster based on its role in sperm development and hormone regulation.
Some studies have found infertile men tend to have lower zinc levels in seminal fluid.
Older studies have also suggested possible improvements in sperm quality with supplementation. They showed taking zinc supplements could increase semen volume, sperm motility and the amount of sperm with normal form and structure.
However, a more recent large, randomised controlled trial involving more than 2,000 couples undergoing infertility treatment found zinc (30 milligram) plus folic acid (5 mg) daily for six months did not improve live birth rates or semen quality compared with taking placebo.
Fertility is influenced by many factors including age, smoking, alcohol use, obesity, and underlying medical conditions. Zinc is only one small part of the picture.
Zinc interactions and formulations
Zinc supplements come in many forms, including zinc amino acid chelate and zinc gluconate. These differences mainly affect absorption and tolerability. The amount of elemental zinc in a tablet or lozenge is what matters most.
Zinc can interact with certain medications, including some antibiotics (such as doxycycline and ciprofloxacin) and diuretics (used as fluid tablets or to reduce blood pressure like hydrochlorothiazide). They reduce absorption of the medicine or alter the mineral balance in the body.
This is why timing and dose matter, particularly for people on regular medications.
Can you take too much zinc?
Yes. And more is not better.
The recommended dietary intake is around 8 mg of elemental zinc per day for women and 14 mg per day for men, which is typically achievable through diet alone.
Supplement doses are often much higher than this. If you buy lozenges to help with a sore throat, check how much zinc they contain.
Long-term high intake can interfere with copper absorption, leading to copper deficiency. This can cause anaemia, nerve problems and, paradoxically, weakened immunity.
Short-term side effects include nausea, abdominal pain, vomiting and a metallic taste.
The upper safe limit for adults is around 40 mg of elemental zinc per day from all sources unless medically supervised.
So, should you take zinc?
For most people eating a balanced diet, a zinc supplement is unlikely to prevent colds, significantly boost immunity, or meaningfully enhance fertility.
Where zinc can be helpful is in cases of confirmed deficiency, or in people with conditions that reduce absorption of nutrients.
For the common cold, zinc lozenges may modestly shorten duration if taken early, but benefits are inconsistent and side effects are common.
If you’re considering zinc supplements, speak with a GP, pharmacist and dietitian first. A simple blood test and dietary review can help determine whether supplementation is actually required.
