Zinc is one of the best-selling trace elements in supplement form, but one question often remains unclear: which form actually reaches the bloodstream? Bisglycinate, picolinate, gluconate, citrate, sulfate and oxide do not provide the same amount of zinc and have not been studied with the same rigour. Here are the human absorption data, the requirements established by the European authority and the pitfalls to avoid.
The essentials
- At a fasting dose of 10 mg, zinc citrate (61.3%) and gluconate (60.9%) are absorbed to a similar extent, while oxide is less well absorbed (49.9%).
- Bisglycinate increased bioavailability by 43.4% compared with gluconate in 12 women; the case for picolinate rests on a single published trial involving 15 people in 1987.
- EFSA sets reference intakes at 7.5 to 12.7 mg/day for women and 9.4 to 16.3 mg/day for men, depending on phytate intake.
- The European tolerable upper intake level for adults is 25 mg/day from all sources combined.
Elemental zinc or the weight of the salt: what should you read on the label?
Look at the amount of elemental zinc, not the weight of the compound. Zinc is always bound to a molecule of varying weight: 100 mg of zinc gluconate provides only around 14 mg of zinc, compared with around 80 mg from 100 mg of oxide. Check that the figure shown refers to “zinc” rather than the entire salt. This is the figure to compare with the 25 mg/day limit.
| Form | Elemental zinc (calculated) | Human data |
|---|---|---|
| Oxide | 80 % | Less well absorbed than citrate and gluconate when fasting |
| Citrate | 32% (dihydrate) | Comparable with gluconate (15 adults) |
| Bisglycinate (glycinate) | 28 to 31% | Better than gluconate in two small trials in women |
| Sulfate | 23 to 36% depending on hydration | Common soluble form in public health |
| Picolinate | 21 % | A single published trial (1987), indirect markers |
| Gluconate | 14 % | The most studied form and usual comparator |
Which form of zinc is best absorbed?
Soluble forms (citrate, gluconate, bisglycinate) perform better than oxide, but none clearly stands out because sufficiently large studies are lacking.
- Citrate, gluconate, oxide. In 2014, a stable-isotope study gave 10 mg of zinc to 15 young adults while fasting: median absorption was 61.3% for citrate, 60.9% for gluconate and 49.9% for oxide, which was poorly or not absorbed in three participants.
- Bisglycinate versus gluconate. After a single dose of 15 mg in 12 women, bisglycinate increased bioavailability by 43.4%. In a 6-week trial using 60 mg/day in young women, plasma zinc increased in every participant in the glycinate group (10 people), with no significant change with gluconate.
- Picolinate. In 1987, 15 volunteers took picolinate, citrate, gluconate (50 mg/day) and placebo for 4 weeks each. Only picolinate increased zinc in hair, urine and red blood cells; serum zinc did not change significantly. The trial has not been replicated.
A 2024 review concludes that glycinate and gluconate appear to be better absorbed, while urging caution: groups usually contain 10 to 15 people. It was funded by a supplement manufacturer. In practice, the dose of elemental zinc and tolerability matter as much as the form. The same reasoning applies to other minerals: see our comparison of magnesium forms.
What reduces zinc absorption?
The main obstacle is phytic acid in whole grains and legumes, which binds zinc in the intestine. The proportion of zinc absorbed from foods ranges from 5% to over 50%, and is lower with a mixed diet than with meals containing only animal products.
- Phytate/zinc ratio. The molar phytate/zinc ratio of a meal is used to estimate the zinc actually available. Certain traditional processes, such as soaking and fermentation, improve it by removing or breaking down phytates.
- Iron supplements. Taking 25 mg or more of elemental iron at the same time as zinc reduces zinc absorption; iron in fortified foods does not cause this problem.
How much zinc do we need each day?
In 2014, EFSA established reference intakes that increase with the amount of phytate consumed (from 300 to 1 200 mg/day, the range observed in Europe):
- adult women: 7.5 to 12.7 mg/day;
- adult men: 9.4 to 16.3 mg/day;
- pregnancy: an additional 1.6 mg/day; breastfeeding: an additional 2.9 mg/day;
- children: 2.9 to 14.2 mg/day depending on age.
Which foods contain the most zinc?
Oysters lead the way, followed by red meat, crustaceans and cheese. Pumpkin seeds and legumes also provide zinc, but their zinc is less available because of phytates. Values from the US database, per serving:
| Food (serving) | Zinc (mg) |
|---|---|
| Raw farmed oysters (85 g) | 32 |
| Roasted beef, bottom sirloin (85 g) | 3.8 |
| Cooked blue crab (85 g) | 3.2 |
| Roasted pumpkin seeds (28 g) | 2.2 |
| Cheddar (42 g) | 1.5 |
| Cooked lentils (½ cup, around 100 g) | 1.3 |
| Egg (1 large) | 0.6 |
Oysters are also rich in selenium; we explore its roles, requirements and food sources.
Who is at risk of inadequate zinc intake?
First, people who eat few animal products. A meta-analysis of 26 studies shows that vegetarians consume an average of 0.88 mg/day less zinc than non-vegetarians and have lower serum zinc, particularly women and vegans. Older adults, pregnant or breastfeeding women, people with inflammatory bowel disease or coeliac disease, those who have undergone bariatric surgery and people with excessive alcohol consumption are also at risk. As with iodine deficiency, diets that exclude food groups call for care.
How can deficiency be recognised, and why is a blood test not enough?
In children, established deficiency causes growth retardation, diarrhoea, hair loss, loss of appetite and more frequent infections. Changes in taste and smell have also been described, as has delayed wound healing in older adults. These signs remain non-specific.
Serum zinc varies with age, sex, time of day, infections and muscle loss, and does not always reflect intake. An isolated result should be interpreted with a healthcare professional.
Zinc and the common cold: what do trials show?
The evidence is uncertain. The 2024 Cochrane review (34 trials, 8 526 participants) concludes that ongoing zinc use may make little or no difference to the risk of a cold (relative risk 0.93, low-certainty evidence). In trials conducted during a cold, duration was reduced by an average of 2.37 days, with very high heterogeneity and low certainty; mild adverse effects, such as an unpleasant taste, probably increase (relative risk 1.34).
Two specialists challenged this analysis, which they argue combines lozenges, nasal sprays and very different doses. Zinc gluconate lozenges were given at 45 to 276 mg/day for 4.5 to 21 days, far above the 25 mg/day limit. No authorised claim concerns the common cold.
What happens with excess zinc?
EFSA sets a limit of 25 mg/day for adults, including during pregnancy and breastfeeding, with lower limits for children; US authorities set theirs at 40 mg/day. Excess intake causes nausea, dizziness, headaches, vomiting and loss of appetite. Over time, 50 mg/day or more for several weeks can inhibit copper absorption; reported cases of copper deficiency involve anaemia and neurological disorders, sometimes after heavy use of zinc-containing denture adhesive creams.
Zinc and quinolone or tetracycline antibiotics interfere with each other: take the antibiotic at least 2 hours before or 4 to 6 hours after zinc. Penicillamine should be separated by at least 1 hour, while thiazide diuretics increase urinary zinc excretion.
What claims can a zinc supplement make?
In Europe, only the claims in Regulation (EU) No 432/2012 are authorised, for products that are at least a “source of zinc”. They include: “Zinc contributes to the normal function of the immune system”, “Zinc contributes to the maintenance of normal skin”, “Zinc contributes to the maintenance of normal nails”, “Zinc contributes to the maintenance of normal vision”, “Zinc contributes to the maintenance of normal bones”, “Zinc contributes to normal fertility and reproduction”, “Zinc contributes to normal cognitive function”, “Zinc contributes to normal carbohydrate metabolism”, “Zinc contributes to normal protein synthesis” and “Zinc contributes to the protection of cells from oxidative stress”.
These wordings describe a physiological role, not an effect on a disease. For more detail, see our articles on oxidative stress and glutathione. Finally, zinc's role in normal carbohydrate metabolism says nothing about an effect on insulin resistance.
Frequently asked questions
Zinc bisglycinate or picolinate?
Compared with gluconate, bisglycinate has the advantage in two trials, picolinate in just one older trial. The only direct comparison, a conference abstract involving 12 women, placed glycinate ahead of picolinate: this is too little evidence to decide. At equal elemental zinc doses, tolerability can guide the choice.
Zinc in the morning or evening, with or without food?
No time of day has shown an advantage. When fasting, as in the 2014 study, zinc avoids the phytates in a meal, but some people experience nausea; taking it with a meal low in whole grains is then a reasonable compromise. The dosage form matters too: see our article on hard capsules, softgels and tablets.
Can zinc and magnesium be taken together?
Yes, at usual doses. Interference with magnesium absorption has only been reported with 142 mg/day of zinc, far above the safety limit.
Zinc and coffee: should they be taken separately?
None of the absorption studies cited here tested coffee: separating them does no harm, but the evidence does not require it.
Does zinc help with acne or hair?
A 2020 meta-analysis found lower serum zinc in people with acne and fewer inflammatory papules with zinc, combining oral and topical use. No authorised claim targets acne. For hair, the authorised claim is: “Zinc contributes to the maintenance of normal hair”.
Zinc and testosterone: what do studies show?
In 1996, 20 weeks of zinc restriction lowered testosterone in 4 young men, and around 30 mg/day of zinc for 3 to 6 months raised it in 9 older men with mild deficiency. The authorised claim is limited to: “Zinc contributes to the maintenance of normal testosterone levels in the blood”.
Does zinc help with sleep?
Human data are too limited to say, and no authorised claim concerns sleep.
What are the contraindications for children or during pregnancy?
In children, the safety limit is lower than in adults; during pregnancy, requirements increase by only 1.6 mg/day and the limit remains 25 mg/day. In these situations, as with the interactions mentioned above, supplementation should be discussed with a healthcare professional.
Conclusion
Zinc requirements depend on the rest of your diet: plenty of phytates increases them, while oysters, meat and cheese help meet them. For supplements, citrate, gluconate and bisglycinate are better absorbed than oxide, but differences between them rest on small trials. The key points: read the elemental zinc amount, stay below 25 mg/day over time and separate zinc from certain antibiotics and high doses of iron.
Sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for zinc. EFSA Journal. 2014;12(10):3844. doi:10.2903/j.efsa.2014.3844
- EFSA. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Version 11, août 2025. efsa.europa.eu
- Règlement (UE) n° 432/2012 de la Commission du 16 mai 2012 établissant une liste des allégations de santé autorisées portant sur les denrées alimentaires. EUR-Lex
- NIH Office of Dietary Supplements. Zinc: Fact Sheet for Health Professionals. ods.od.nih.gov
- Wegmüller R, Tay F, Zeder C, Brnic M, Hurrell RF. Zinc absorption by young adults from supplemental zinc citrate is comparable with that from zinc gluconate and higher than from zinc oxide. J Nutr. 2014;144(2):132-136. doi:10.3945/jn.113.181487
- Gandia P, Bour D, Maurette JM, et al. A bioavailability study comparing two oral formulations containing zinc (Zn bis-glycinate vs. Zn gluconate) after a single administration to twelve healthy female volunteers. Int J Vitam Nutr Res. 2007;77(4):243-248. doi:10.1024/0300-9831.77.4.243
- DiSilvestro RA, Koch E, Rakes L. Moderately high dose zinc gluconate or zinc glycinate: effects on plasma zinc and erythrocyte superoxide dismutase activities in young adult women. Biol Trace Elem Res. 2015;168(1):11-14. doi:10.1007/s12011-015-0334-3
- Barrie SA, Wright JV, Pizzorno JE, Kutter E, Barron PC. Comparative absorption of zinc picolinate, zinc citrate and zinc gluconate in humans. Agents Actions. 1987;21(1-2):223-228. doi:10.1007/BF01974946
- Devarshi PP, Mao Q, Grant RW, Hazels Mitmesser S. Comparative absorption and bioavailability of various chemical forms of zinc in humans: a narrative review. Nutrients. 2024;16(24):4269. doi:10.3390/nu16244269
- Gibson RS, Raboy V, King JC. Implications of phytate in plant-based foods for iron and zinc bioavailability, setting dietary requirements, and formulating programs and policies. Nutr Rev. 2018;76(11):793-804. doi:10.1093/nutrit/nuy028
- Foster M, Chu A, Petocz P, Samman S. Effect of vegetarian diets on zinc status: a systematic review and meta-analysis of studies in humans. J Sci Food Agric. 2013;93(10):2362-2371. doi:10.1002/jsfa.6179
- Nault D, Machingo TA, Shipper AG, et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev. 2024;5:CD014914. doi:10.1002/14651858.CD014914.pub2
- Hemilä H, Chalker E. Shortcomings in the Cochrane review on zinc for the common cold (2024). Front Med. 2024;11:1470004. doi:10.3389/fmed.2024.1470004
- Prasad AS, Mantzoros CS, Beck FW, Hess JW, Brewer GJ. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996;12(5):344-348. doi:10.1016/s0899-9007(96)80058-x
- Yee BE, Richards P, Sui JY, Marsch AF. Serum zinc levels and efficacy of zinc treatment in acne vulgaris: a systematic review and meta-analysis. Dermatol Ther. 2020;33(6):e14252. doi:10.1111/dth.14252
Food supplements are not a substitute for a varied, balanced diet and a healthy lifestyle. Ask a healthcare professional for advice if you take medication or are pregnant or breastfeeding.
