Is this the blockbuster supplement everyone should take?

It may not be the first supplement you think about, but zinc ranks among the most important minerals in our diets. It’s involved in many aspects of cellular metabolism, prompting the catalytic activity of roughly 100 enzymes. It plays a key role in our immune systems, protein synthesis, DNA synthesis, and cell division. In addition, zinc may be a potent weapon against chronic liver disease. It even helps our wounds heal.

Given all that, we’d better be sure we’re getting enough zinc, right? And yet, according to data published by the NIH’s Office of Dietary Supplements, some people are falling short of the recommended daily allowance (RDA) for zinc—which we’ll dive into below. Meanwhile, an estimated 35%-45% of adults aged 60 years or older have zinc intakes below daily recommended levels, and zinc consumption is likely below 50% of the RDA for adults from the estimated 2%-4% of US households that are food-insufficient, according to the NIH.

So how much zinc should we be consuming, and in what form? What are the impacts of zinc deficiency? And who should consider upping their intake?

Sources of zinc

According to the NIH fact sheet, the daily recommended intake of zinc for adults over the age of 19 is 11 mg for men and 8 mg for women (which is upped to 11 mg for pregnant women and 12 mg for lactating women).

Fortunately, a wide variety of foods contain zinc. Way at the top of the list are oysters, which contain roughly 74 mg per 3 oz serving. Other foods that provide zinc include beef, pork, seafood (like crab and lobster), beans, whole grains, and dairy products. The phytates present in foods like cereals and legumes bind zinc and inhibit its absorption, which means that the bioavailability of the mineral tends to be lower in plant-based foods compared to animal products. 

Zinc supplements come in different forms, including zinc gluconate, zinc sulfate, and zinc acetate. Research gaps leave it unclear whether there are differences in the absorption, bioavailability, or tolerability among these forms.

Impacts of zinc deficiency 

Those not getting enough zinc may experience loss of appetite and impaired immune function. In acute cases, symptoms can include hair loss, diarrhea, impotence, hypogonadism (in men), eye and skin lesions, weight loss, deficiencies in wound healing, taste abnormalities, and mental lethargy. In children, it can result in growth retardation and delayed sexual maturation, notes the NIIH. 

A prolonged zinc deficit can lead to several adverse health conditions. Chief among these is an impaired immune system. A zinc deficiency depresses immune function, by impairing macrophage and neutrophil functions, natural killer cell activity, and complement activity. The body relies on zinc to activate T-lymphocytes, and researchers have observed reduced lymphocyte proliferation response to mitogens in those with low zinc levels. As a result, having a zinc deficiency can lead to an increased risk of pneumonia and other infections.

Those who aren’t getting enough zinc may also experience slower wound healing, and in acute cases can develop chronic leg ulcers. In addition, zinc deficiency can result in diarrhea and accelerated age-related macular degeneration.

A 2020 review published in The American Journal of Tropical Medicine and Hygiene confirmed that zinc levels appear to have a direct impact on the duration of common colds. Researchers analyzed the findings of 20 studies and found that, while vitamin C may be the only micronutrient that can help prevent cold incidence or reduce symptom severity among healthy adults, zinc supplementation was linked to a reduction in cold duration by 2.25 days.

On the flip side, some research shows that too much zinc can lead to decreased immunity, chills, headache, fatigue, and fever. Experts at the Mayo Clinic recommend not going over the upper limit, which is 40 mg of zinc per day for adults. Of note, the use of intranasal zinc is not advised, as it has been linked with loss of smell, in some cases, permanently.

In addition, it’s also important to be aware that supplemental zinc can interact with medications, including certain antibiotics, diuretics, and penicillamine (a drug used to treat rheumatoid arthritis), and may interfere with absorption of iron and copper. 

Who’s most at risk of zinc deficiency? 

Zinc is distributed throughout the body as a component of certain proteins and nucleic acids, which makes it very tricky to measure a person’s levels using lab tests. As such, physicians typically consider deficiency symptoms and risk factors when figuring out whether to recommend zinc supplements. 

According to the Mayo Clinic, clear signs of zinc deficiency in the United States are uncommon. Still, it’s important to know if you’re among those who are at risk of inadequate zinc intake or absorption. This includes those with gastrointestinal and digestive disorders, like ulcerative colitis, Crohn’s disease, and short bowel syndrome, who are likely to have lower rates of zinc absorption and higher rates of endogenous zinc losses, notes the NIH. This may also apply to those with malabsorption syndrome, chronic liver disease, chronic renal disease, sickle cell disease, or diabetes.

People who don’t eat animal products may also be at risk of zinc deficiency, due to the lower bioavailability of zinc in plant-based foods. According to the NIH, some vegetarians require as much as 50% of the recommended daily zinc intake in supplement form.

Other populations that may require zinc supplementation include alcoholics, some 30%–50% of whom have low zinc levels because ethanol consumption decreases the intestinal absorption of zinc. Pregnant and lactating women also require additional zinc, due to the high fetal requirements for the mineral.

A defense against COVID?

As a final note, a handful of recent articles suggest that zinc could serve a key role in helping us defend against the coronavirus. According to a 2020 article published in Frontiers in Immunology, the mineral could potentially work as a preventive and therapeutic agent, alone or in combination with other strategies, against SARS-CoV-2.

Of note, the authors wrote, the majority of the risk groups for COVID-19 are also groups that were associated with zinc deficiency. 

“As zinc is essential to preserv[ing] natural tissue barriers such as the respiratory epithelium, preventing pathogen entry, [and] for a balanced function of the immune system and the redox system, zinc deficiency can probably be added to the factors predisposing individuals to infection and detrimental progression of COVID-19,” they wrote.

In conclusion, they noted, “Although data specifically on SARS-CoV2 are unfortunately still pending, and randomized controlled studies have not been conducted, the enumerated evidence from the literature strongly suggests great benefits of zinc supplementation.”