Zinc: needs, supplements and the risks of excess

Zinc is mainly found in oysters and seafood, meat, dairy products, eggs, legumes, whole grains, nuts, and seeds, such as pumpkin seeds. Zinc from animal sources is better absorbed. Phytates in grains, legumes, and seeds reduce its absorption, without making these foods useless: soaking, sprouting, or fermentation reduce some of it.

This is why EFSA adjusts its reference values based on the phytate content of the diet: for adults, needs range from about 7.5 to 12.7 mg per day in women and 9.4 to 16.3 mg in men, with the higher values corresponding to phytate-rich diets. In the United States, recommended intakes are 11 mg for men and 8 mg for women.

Deficiency remains rare in wealthy countries. It mainly affects people with digestive disease (Crohn's disease, celiac disease, bariatric surgery), excessive alcohol consumption, a very restrictive diet, or certain older adults. Hair loss, fatigue, taste disturbances, or repeated infections aren't enough to conclude there's a deficiency: these signs have many other causes. Blood testing itself has limits, since levels vary with time of day, inflammation, and meals.

The 2024 Cochrane review pooled 34 studies and 8,526 participants. For prevention, zinc reduced the risk of catching a cold little or not at all. For treatment, taken after symptoms began, it may have shortened colds by about two days, with low certainty and highly variable results. It probably increased mild adverse effects, such as nausea or a bad taste in the mouth. The products, forms (lozenges, syrups, nasal sprays), and doses were very different.

At a high dose, zinc causes nausea, vomiting, abdominal cramps, and diarrhea. Taken for a long time beyond the limits, it blocks copper absorption. This copper deficiency can lead to anemia, a drop in white blood cells, and sometimes lasting neurological problems. For more, see copper.

EFSA sets the upper limit at 25 mg per day for adults, the United States at 40 mg. These values cover total intake, food and supplements combined, and aren't targets to reach. Check the amount of "elemental" zinc on the label and add up your products: multivitamins, cold lozenges, and "skin" or "immunity" supplements often contain it.

Zinc reduces the absorption of certain antibiotics (tetracyclines and quinolones) and of penicillamine. Conversely, certain diuretics increase its urinary loss. The interval between doses depends on the exact medication: ask your pharmacist rather than applying a general rule. High-dose iron and calcium can also interfere with its absorption.

Pregnancy and breastfeeding slightly increase needs, without justifying routine supplementation. In children, an adult dose should never be applied directly. The WHO recommends zinc in treating acute diarrhea in children, but within a specific care framework, alongside oral rehydration. Kidney or digestive disease, digestive surgery, or long-term treatment warrant advice before any supplement.

For iron, another mineral whose absorption depends on phytates, see dietary iron.