Zinc is present in many different foods. Foods with the highest zinc content include oysters, crab and beef. Phytates, which bind to zinc and limit its absorption into the body, are often present in plants — but plant-based foods, such as pumpkin seeds and oatmeal, can still be good sources of the mineral.

So, what does zinc do? Studies show that zinc is important in almost all aspects of the immune system: It helps skin cells and cells lining our organs prevent pathogens from entering, and it keeps the thymus and bone marrow, which are responsible for generating immune cells, functioning normally.

Zinc “crops up in all parts of the immune system,” says Sophie Hambleton, an immunologist at Newcastle University in the UK – and zinc-deficient people show a wide range of immune dysfunctions.

Most of the research to date has focused on the role of zinc in the innate immune system, the body’s frontline defence that launches fast, non-specific attacks against foreign invaders.

Zinc appears to be involved in making physical barriers such as the cells that line our organs more resistant to invasion, as well as ensuring the proper functioning of macrophages, key white blood cells that gobble up pathogens and send out chemical signals to recruit other cellular soldiers.

To ensure that there’s enough zinc to carry out these many jobs, concentrations of the mineral within the body are tightly controlled. At the onset of an infection, for example, immune cells such as macrophages rapidly produce a zinc-transporting protein called ZIP8. This protein controls how much zinc enters these cells, which is important for maintaining the cells’ ability to mop up pathogens and regulating the production of important defence-related molecules, including chemical messengers called cytokines, says Daren Knoell, a zinc biologist at the University of Nebraska, and others have found.

More recent work has started to reveal that zinc is also important for the adaptive immune system, which uses memories of prior threats to launch pathogen-specific attacks via antibodies and T cells. In 2019, Hambleton and her colleagues reported that a mutation in another zinc transporter, ZIP7, caused a disease in which patients lack B cells, antibody-producing immune cells that we continuously generate throughout our lives.

Further experiments in mice with these same mutations revealed that a lack of ZIP7 reduced the concentrations of zinc within immature B cells, impairing their maturation.

Although it is still unclear what this means for the broader role of ZIP7 in people without this mutation, Hambleton says that it is possible that a defect in ZIP7 may be one way in which an overall deficiency of zinc might lead to problems in immune function.

Graphic showing where zinc is important in immune system: skin, blood and immune organs like the thymus and bone marrow.

Zinc is important for a wide range of processes in the immune system, from keeping physical barriers intact to ensuring the proper functioning of the many different types of immune cells.

How much zinc does a person need?

Given how important zinc is to a healthy immune system — and the difficulty of knowing whether a person might be deficient — Rink says zinc supplementation is probably a good idea, especially for people who are at higher risk of being deficient, such as vegetarians, vegans and the elderly. (Rink has consulted for or received research grants from three companies that sell zinc supplements).

Most nutritional supplements are safe and don’t cause any serious side-effects at the recommended daily intake, eight milligrams and 11 milligrams for women and men, respectively, but Rink warns that at very high concentrations zinc can have adverse effects.

In 2009, the US Food and Drug Administration warned against the use of Zicam nasal spray and swabs, a common cold remedy containing zinc levels so high that it led to a loss of the sense of smell. Due to this and other potential harms, experts recommend that adults consume no more than 40 milligrams of

Most pharmacies stock over-the-counter zinc supplements. Some studies suggest taking supplements might help reduce the duration and severity of respiratory infections such as the common cold. But open questions — such as the best time to take these supplements, and whether they benefit people who aren’t zinc deficient — remain.

Although clinical trials in humans are scarce, there have been a handful that have examined the effects of zinc supplementation during viral infections. A 2021 review of two dozen clinical trials indicated that in healthy people, taking zinc supplements either as lozenges or nasal sprays at the onset of illness may reduce the duration of the common cold and other respiratory infections by a few days.

The study also looked at chronic supplementation, and found evidence that taking zinc supplements daily for seven months to a year might help stave off the effects of respiratory infections, though it did not appear to prevent the common cold.

Hambleton notes, however, that while it’s important to make sure you’re getting enough zinc in your diet, manipulating zinc levels in specific parts of the immune system is not easy because zinc is distributed in different ways across the body.

“It’s very simplistic to think that because zinc is required for immunity, more zinc equals more immunity,” she says.

Many open questions remain. For one, the authors of that 2021 review note that there were limitations to the available trials, such as small sample sizes. In addition, the time frame for zinc’s benefits is unclear.

Most of the trials looking at the benefits of zinc after infection reported that supplements work only within 24 hours of when symptoms begin — but the team found evidence that window might be longer, and that zinc might be beneficial even when consumed up to three days after the onset of symptoms. And we need better zinc supplements, Knoell says.

Most now come in salt form, as zinc sulphate or chloride, but these are not readily taken up by the body, so better formulations would be beneficial, he adds.

There’s also the question of whether certain people are genetically programmed to have a harder time absorbing zinc into their body than others. And researchers also are interested in investigating possible drugs that might target zinc transporters in people who have problems in those proteins.

“We’re starting to ask and answer those questions now in animal models,” Knoell says. “The excitement will be, of course, if some of that translates to the human condition.”

• A Knowable Magazine report