Zinc

What it is

Zinc is a metal the body uses in three broad ways. It is catalytic, as a working part of enzymes. It is structural: in copper-zinc superoxide dismutase, an antioxidant enzyme, copper does the chemistry and zinc holds the shape. And it is regulatory, as part of the "zinc finger" proteins that control gene expression.^[1] Because zinc is involved in so many processes, the signs of a mild shortfall are vague and varied. Overt deficiency is not common in North America.^[1]

Most zinc is absorbed in the small intestine, and the body balances how much it absorbs against how much it secretes back into the gut, adapting to how much zinc the diet supplies.^[1] Red meat, some seafood and whole grains are the richest sources. Milling strips up to 80 percent of the zinc from grains, and many breakfast cereals are fortified.^[1] Phytate, a compound in grains and legumes, binds zinc and lowers absorption. The Institute of Medicine estimated that people on vegetarian diets built on grains and legumes may need up to 50 percent more zinc. Long-term heavy drinking also lowers absorption and raises losses.^[1]

In supplements, zinc is always bound to something else, and the form changes how much zinc you get. Replenish uses zinc citrate, the zinc salt of citric acid. In a crossover study, 15 healthy adults absorbed about 61 percent of a 10 mg dose of zinc from zinc citrate and from zinc gluconate taken without food, compared with about 50 percent from zinc oxide.^[2]

How much adults need

Source: Institute of Medicine, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001), chapter 12.^[1] The UL covers zinc from food, water and supplements combined. RDA = Recommended Dietary Allowance; UL = Tolerable Upper Intake Level.

Amount in Replenish: confirmed at launch

The RDA is set to cover the needs of 97 to 98 percent of healthy people, so most need a little less. When the report was written, the median intake from food in the United States was about 14 mg a day for men and 9 mg for women, close to or above the RDA.^[1] Those medians describe people eating normal amounts. Someone who is eating much less than usual, or eating little meat or seafood, takes in less zinc along with everything else; what to prioritize on those days is in what to eat when you're eating less.

The UL of 40 mg is not a target. It is the highest daily intake judged unlikely to cause harm, and it applies to total intake from every source. It is based on a drop in a copper-dependent enzyme seen when adults took about 60 mg a day in total.^[1]

What the evidence says

Colds. Zinc is best known as a cold remedy, and the evidence is mixed. A 2024 Cochrane systematic review pooled 34 placebo-controlled trials with 8,526 participants. Taking zinc regularly to prevent colds may make little or no difference to the chance of catching one (risk ratio 0.93; 9 trials, low-certainty evidence). Taken once a cold has started, zinc may shorten it by about 2.4 days on average, but the trials varied widely and the certainty was rated low. Zinc used as a cold treatment probably increased non-serious adverse events, such as a bad taste or stomach upset.^[3] Half of the trials used lozenges, and in those, zinc gluconate was given at 45 to 276 mg a day for 4.5 to 21 days: short courses at doses well beyond a daily nutrient amount.^[3]

Eyes. The Age-Related Eye Disease Study randomized 3,640 people aged 55 to 80 with signs of age-related macular degeneration to antioxidants, zinc, both, or placebo for an average of 6.3 years. The zinc arm took 80 mg of zinc with 2 mg of copper a day. Antioxidants plus zinc reduced the odds of progressing to advanced disease compared with placebo (odds ratio 0.72), and in the higher-risk group zinc alone did too.^[4] That result applies to people who already have the eye disease, at a dose twice the UL, and whether it fits is a question for an eye doctor. It says nothing about zinc for people without the condition.

Deficiency. Where zinc clearly matters is in getting enough. In children with a shortfall, slow growth is a primary feature and responds to zinc. Severe deficiency has been seen in patients fed intravenously without enough added zinc.^[1] For healthy adults who already meet the RDA, there is no good evidence that more zinc adds anything.

Safety and interactions

Copper. The main long-term risk of too much zinc is that it lowers copper status. The UL is built on a study in which women taking 50 mg a day of supplemental zinc, about 60 mg in total, showed a fall in a copper-dependent enzyme over 10 weeks.^[1] Large single doses of zinc salts can cause stomach pain, vomiting, cramps and diarrhea, and stomach upset has been reported at 50 to 150 mg a day of supplemental zinc.^[1] If you take a separate zinc supplement, a multivitamin and cold lozenges, add them up.

Iron. Iron supplements taken at the same time can reduce how much zinc is absorbed.^[1]

Quinolone and tetracycline antibiotics. Zinc binds these antibiotics in the gut. In a study of 12 healthy men, a week of a multivitamin with zinc lowered ciprofloxacin exposure (area under the curve) from 14.5 to 11.3 µg·h/mL; the authors could not say which ingredient was responsible.^[5] The ciprofloxacin label says to take the antibiotic at least 2 hours before or 6 hours after products containing calcium, iron or zinc.^[6] In 7 volunteers, a 45 mg dose of zinc as zinc sulfate taken with tetracycline cut tetracycline absorption by about 30 percent, though doxycycline was not significantly affected.^[7]

Penicillamine. The label for penicillamine, a chelating drug used for Wilson's disease and some other conditions, says to take it at least 1 hour apart from any zinc- or iron-containing preparation, because metals bind the drug in the gut.^[8]

Thiazide diuretics. In patients with high blood pressure, long-term treatment with hydrochlorothiazide, alone or with amiloride, raised the amount of zinc lost in urine, though blood zinc levels were similar to controls.^[9]

If you take prescription medicine, ask your pharmacist or prescriber before adding a supplement.

In Replenish

Replenish contains zinc as zinc citrate. It sits alongside the 4 electrolyte minerals rather than among them, which is why the label reads "4 electrolyte minerals plus zinc". Together with six vitamins, it is part of how Replenish provides key vitamins and minerals.^† The amount per serving is published with the Supplement Facts panel on the Replenish page. Other minerals in the formula are covered in the magnesium and calcium monographs, and how a supplement fits around smaller meals is in what supplements to take with a GLP-1.