Zinc by form

Reading the label

Two numbers that look alike and are not

Every zinc supplement is zinc bound to something else, and the something else is most of the weight. Zinc picolinate is zinc plus two picolinic acid molecules, and the zinc is about a fifth of it. Zinc gluconate is one seventh zinc. Zinc oxide is four fifths zinc. The elemental amount, the zinc itself, is what your body counts and what every dose recommendation refers to.

In the United States the Supplement Facts panel on the back is required to list the elemental amount: a line reading Zinc (as zinc picolinate) 22 mg means 22 mg of zinc. The number on the front of the bottle, or in the product name, is sometimes the weight of the whole compound. A product called "Zinc Picolinate 50 mg" can contain either 50 mg of zinc or 50 mg of zinc picolinate, which is about 10.5 mg of zinc, and the only way to know is the panel on the back. Turn the bottle around before comparing two products or two prices.

Reference

Elemental zinc in each form

Calculated from molecular weight. Where the commercial form is a hydrate, the water is included, because it is in the capsule too. The third column is how much of the compound you need to get 15 mg of zinc, a typical supplemental dose.

Zinc 65.38; molecular weights from the formulas shown. Zinc citrate sold as the dihydrate is about 32% zinc rather than 34%.

The evidence

What the human absorption trials actually show

Citrate and gluconate are equal, and oxide is worse. The cleanest comparison is a 2014 Swiss trial that used two stable zinc isotopes to measure how much of a 10 mg dose 15 healthy adults absorbed from each form, without food. Zinc citrate came in at a median 61.3% and zinc gluconate at 60.9%, no difference between them. Zinc oxide was significantly lower at 49.9%, and three of the fifteen people absorbed little or none of it. Oxide is the form in most cheap multivitamins (Wegmüller et al., J Nutr 2014;144:132-6).

Bisglycinate has beaten gluconate twice, in small studies. A single-dose crossover in 12 women found 43% higher zinc exposure in the blood from bisglycinate than from gluconate at the same 15 mg dose (Gandia et al., Int J Vitam Nutr Res 2007;77:243-8). A six-week study in young women at 60 mg a day found plasma zinc rose in everyone taking glycinate and did not change significantly on gluconate or placebo, with ten people per group (DiSilvestro et al., Biol Trace Elem Res 2015;168:11-4). Both are small, and neither used isotopes, but they point the same way.

Picolinate rests on one trial from 1987. Fifteen volunteers rotated through four weeks each of zinc picolinate, zinc citrate, zinc gluconate and placebo at 50 mg of zinc a day. Hair, urine and red-cell zinc rose significantly on picolinate and not on the other two; serum zinc did not change significantly on any of them (Barrie et al., Agents Actions 1987;21:223-8). That is the whole basis of the "best-absorbed form" claim you will see on picolinate labels. It has never been repeated with isotope methods, the markers it used are indirect, and a 2015 single-dose comparison summarized in a 2024 review found picolinate no better than oxide on the day. Picolinate is a perfectly usable form. It is not a demonstrated upgrade, and it usually costs more per milligram of zinc.

The 2024 review that ranks glycinate first was written by a supplement company. A narrative review in Nutrients concluded that zinc glycinate and zinc gluconate are the best-absorbed forms (Devarshi et al., Nutrients 2024;16:4269). Its four authors are employees of Pharmavite, which makes Nature Made. The conclusion matches the trials above, so it is probably right, but it is worth knowing who wrote it.

What this means in practice. Sulfate, gluconate, citrate and bisglycinate all deliver zinc reliably. Oxide is the one to avoid if you are taking zinc on purpose, because for some people it barely works. Beyond that, the differences between the good forms are smaller than the difference between taking zinc with or without a phytate-rich meal (whole grains, legumes), which can cut absorption substantially. Take it between meals or with a protein meal, keep the daily total under 40 mg, and buy the cheapest soluble form per milligram of zinc.

Worth knowing

Lozenges, copper and the cold studies

The zinc lozenge trials for the common cold used zinc acetate or zinc gluconate at 75 mg or more of zinc a day, dissolved slowly in the mouth, started within 24 hours of symptoms. That is a different use from a daily capsule, with its own evidence and its own problems, and it is covered in the zinc entry.

Zinc and copper compete for absorption. Above the 40 mg upper limit for weeks, zinc can produce a copper deficiency that shows up as anemia and, later, nerve damage. Anyone taking 50 mg a day for more than a few weeks should either add 1 to 2 mg of copper or, better, stop at the shortfall dose. Zinc L-carnosine is on the table above because people ask, but it is a gut-lining compound taken for the carnosine complex, not a way to supplement zinc.

Food covers most people: three ounces of oysters carry around 30 mg of zinc, beef and lamb 4 to 7 mg per serving, pumpkin seeds about 2 mg an ounce. See how much food matches your dose →

Questions

Common questions

How much zinc is actually in zinc picolinate?

Zinc picolinate is about 21% zinc by weight, so 50 mg of zinc picolinate holds about 10.5 mg of zinc. US Supplement Facts panels are required to state the elemental amount, so a label reading "Zinc (as zinc picolinate) 22 mg" means 22 mg of zinc, from roughly 104 mg of the compound. The conversion only matters when a front label or a product name gives the weight of the whole compound.

Which zinc form is best absorbed?

The strongest direct evidence is a 2014 isotope trial in 15 adults: zinc citrate and zinc gluconate were absorbed about equally, around 61% of the dose without food, and zinc oxide was lower at about 50%, with three people absorbing almost none from oxide. Zinc bisglycinate beat gluconate in two small studies, one single-dose and one six-week. Zinc picolinate rests on a single 1987 trial of 15 people that measured hair, urine and red-cell zinc, not absorption. Any soluble form taken away from a high-phytate meal does the job; oxide is the one to avoid.

Is zinc picolinate better than zinc gluconate or citrate?

Not on current evidence. The claim comes from one four-week crossover trial in 1987 with 15 volunteers taking 50 mg a day, in which hair, urine and red-cell zinc rose on picolinate and not on citrate or gluconate, while serum zinc did not change significantly on any of them. It has not been repeated with isotope methods, and a 2015 single-dose comparison found picolinate no better than oxide. Picolinate is a reasonable form; it is not a proven upgrade, and it usually costs more per milligram of zinc.

How much zinc is too much?

The US tolerable upper intake level for adults is 40 mg a day of elemental zinc from all sources. Above that for weeks or months, zinc blocks copper absorption and can cause a copper deficiency that shows up as anemia and nerve symptoms. Daily needs are 11 mg for men and 8 mg for women; a 15 to 25 mg supplement covers a shortfall, and 50 mg a day is a short-term dose, not a maintenance one.

About the author

Who built this

Daniel Edlund is a Le Cordon Bleu-trained private chef in Los Angeles, a certified personal trainer and strength coach with thirty years of training behind him, and the author of The Complete Supplement Guide, which grades 147 entries against the clinical literature. He has no financial interest in any supplement brand named on this page, receives no commission on anything sold here, and the forms are ranked by the trials, not by what sells.

More about Daniel →

This page is information, not medical advice. Supplements interact with prescription medication and with each other, and the right answer depends on your own bloodwork and history. Talk to your doctor before starting anything, particularly if you are pregnant, nursing, managing a health condition, or already taking medication.

Go further

The guide behind the tool

Zinc has its own entry in The Complete Supplement Guide: the dose the research supports, the form, what it does and does not do for immunity and testosterone, and what to avoid stacking it with. 177 pages, 147 entries, graded against the clinical evidence.

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The zinc entry → · Magnesium by form → · Food vs. Capsule → · All 147 entries, graded →