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What Is Zinc Picolinate? The 1987 Study, Elemental Zinc and Forms
Zinc picolinate is zinc bound to picolinic acid, a compound the body itself makes from the amino acid tryptophan; it is about 21% zinc by weight, and its reputation for absorption rests on one 1987 study of 15 volunteers that measured hair, urine and red-cell zinc rather than absorption itself, and no tracer study has tested it since.1, 2, 3 The same wording applies to every form: zinc contributes to the normal function of the immune system and to the maintenance of normal skin, hair and nails.4 UK adults need about 9.5 mg a day for men and 7 mg for women, and the NHS says: "Do not take more than 25mg of zinc supplements a day unless advised to by a doctor."5 Part of the Wellgard zinc guide; see also which type of zinc is best.
What is zinc picolinate, and what is picolinic acid?
Picolinic acid is a small organic acid the body produces from tryptophan along the kynurenine pathway; a 2009 review calls it "an endogenous metabolite of L-tryptophan" whose main physiological function "is yet to be established".1 Two picolinate molecules bind one zinc atom, which is why some labels say "chelated": the word describes the bond. Once the capsule dissolves, the zinc is zinc. The authorised sentences for zinc on the GB register attach to the zinc, not the carrier, no form has a claim of its own, and no absorption comparison is an authorised claim for any of them.4
How much elemental zinc is in zinc picolinate?
About 21%. Picolinic acid has a formula weight of about 123 and zinc about 65, so zinc picolinate, with two picolinates to each zinc, weighs about 310, of which zinc is 65: 100 mg of the compound carries about 21 mg of zinc, and 22 mg of zinc needs roughly 104 mg of zinc picolinate.
| Form | Zinc in 100 mg of the compound | Human absorption evidence |
|---|---|---|
| Zinc picolinate | about 21 mg | One 1987 crossover, 15 people, 50 mg a day for four weeks, read in hair, urine, red cells and serum2 |
| Zinc citrate | about 31 to 34 mg | 2014 tracer study, 15 adults, 10 mg without food: 61.3% absorbed3 |
| Zinc gluconate | about 14 mg | Same study: 60.9%, not different from citrate3 |
| Zinc oxide | about 80 mg | Same study: 49.9%, significantly lower (P < 0.01); three of the 15 absorbed "little or no" zinc from it3 |
A UK label does the arithmetic for you: food supplement labels give the zinc as elemental zinc with a percentage of the 10 mg nutrient reference value, so "zinc 22 mg (220% NRV)" means 22 mg of zinc, not 22 mg of compound.6 That is the figure to hold against the NHS line: at 22 mg a capsule you are inside 25 mg only if nothing else you take carries zinc; at 50 mg you are at twice the line.5 How much zinc a day sets out the UK figures.
What did the 1987 study find?
It was a double-blind, four-period crossover in 15 healthy volunteers, each rotating through four-week periods of zinc picolinate, zinc citrate and zinc gluconate, each supplying 50 mg of elemental zinc a day, and placebo. After four weeks, hair, urine and red-cell zinc had risen significantly during the picolinate period (p < 0.005, p < 0.001 and p < 0.001); there was no significant change in any of these measures during the gluconate, citrate or placebo periods; and serum zinc showed only "a small, insignificant rise" during picolinate, citrate and placebo alike. The authors concluded that the results "suggest that zinc absorption in humans can be improved by complexing zinc with picolinic acid".2 That is 15 people, 50 mg a day, and absorption inferred from where zinc turned up afterwards rather than measured as it crossed the gut. The study is consistent with picolinate being absorbed well; it is not a measurement of how well.
What has been studied since 1987?
Not picolinate's absorption. The most rigorous comparison of zinc forms, published in 2014, used a double-isotope tracer in 15 healthy adults given 10 mg of zinc without food in a randomised, double-masked crossover: median absorption was 61.3% from zinc citrate and 60.9% from zinc gluconate, with no difference between them, and 49.9% from zinc oxide, significantly lower (P < 0.01), a result the authors tie to a supplement "given without food".3 Picolinate was not tested, so the two studies cannot be laid side by side. Later trials used picolinate as the zinc source without comparing it with another form; in one, 73 Japanese patients with a taste disorder attributed to zinc deficiency showed no significant difference in subjective symptoms after three months, but a significantly better filter-paper taste test and a higher serum zinc.7 What we don't know: whether picolinate's absorption differs from citrate or gluconate when measured directly, and whether the form changes anything a person would notice, because the comparisons measure absorption and blood markers, not outcomes.
How does zinc picolinate compare with citrate, gluconate and oxide?
On the facts, without a ranking: picolinate has one 1987 study using indirect markers; citrate and gluconate have one 2014 tracer study in which they were absorbed equally; oxide, in the same study, was absorbed less when taken without food and was not tested with a meal, which is how most multi-nutrient products are taken.2, 3 Nobody has put the four forms through the same tracer protocol; until someone does, the label figure and the 25 mg line are the two things a shopper can act on.
Does zinc picolinate have different side effects?
Nothing in the 1987 abstract reports side effects, so the question is answered from what is known about zinc at a given dose.2 In a 1987 Australian trial, 47 healthy volunteers took 50 mg of zinc three times a day for six weeks: headaches, abdominal cramps, nausea, loss of appetite and vomiting were reported by 84% of the women and 18% of the men.8 A picolinate capsule at 22 or 25 mg of zinc is a higher single dose than most multi-nutrient products carry, which is a reason to take it with a meal, not a reason to expect a different kind of side effect. Can you take too much zinc covers higher doses.
Who should not take zinc picolinate, and what should you avoid taking it with?
The same people, and the same things, as for any zinc. The NHS line comes first: "Do not take more than 25mg of zinc supplements a day unless advised to by a doctor", because "Taking high doses of zinc reduces the amount of copper the body can absorb. This can lead to anaemia and weakening of the bones."5 No NHS or regulatory document sets a zinc to copper ratio, so the forum question "what ratio for 50 mg of zinc picolinate" has no official answer; copper has its own NHS line of 10 mg a day from food, water and supplements, and 50 mg of zinc a day is a dose for a doctor to advise.5 Zinc and copper sets out the evidence.
Count the total: a multivitamin, a vitamin C and zinc product and a picolinate capsule can together pass 25 mg; vitamin C and zinc together covers that stacking. With antibiotics, the NHS says of ciprofloxacin: "Leave 2 hours in between taking supplements and your dose of ciprofloxacin tablets or liquid"; with tetracyclines such as doxycycline and lymecycline, tell your pharmacist.9 Iron reduces zinc absorption "if given together in a supplement", though not in a meal, so take an iron tablet at a different time of day.10 Anyone on penicillamine or another long-term medicine asks a pharmacist first. In pregnancy and breastfeeding the 25 mg line still applies and the person to ask is your GP or midwife; for a child, a pharmacist or GP. Symptoms need a GP: signs of zinc deficiency explains why the blood test is hard to read, and the vitamins and minerals guide covers the other minerals.
Frequently asked questions
Is it safe to take zinc picolinate every day?
Within the NHS line, yes: 25 mg or less of zinc a day from every supplement you take, unless a doctor has advised more.5 The 1987 study ran four weeks at 50 mg; the NHS figure is the one for daily use over years.2
What is the difference between zinc picolinate and zinc?
Picolinate is one of the carriers that deliver zinc in a capsule. "Zinc 22 mg" on a UK label is the elemental zinc, whatever the carrier, and the figure to compare against 25 mg.6
Is zinc picolinate better than zinc citrate or zinc gluconate?
Not shown either way. The 1987 study's indirect markers rose only with picolinate; the 2014 tracer study found citrate and gluconate absorbed equally and did not include picolinate; no tracer study has compared picolinate with either.2, 3
Is zinc picolinate good for men?
The wording that applies to men applies to zinc in any form: zinc contributes to the maintenance of normal testosterone levels in the blood and to normal fertility and reproduction.4 The picolinate studies measured zinc markers and taste, nothing specific to men; the testosterone and fertility trials are set out in what does zinc do for men.2, 7
Can I take zinc picolinate before bed?
You can, with food if evening capsules make you queasy. Zinc has no authorised sleep wording in any form; which vitamin deficiency affects sleep reports the zinc sleep trials as they are.
Sources
- Grant RS, et al. The physiological action of picolinic acid in the human brain. International Journal of Tryptophan Research, 2009. PubMed 22084583.
- Barrie SA, et al. Comparative absorption of zinc picolinate, zinc citrate and zinc gluconate in humans. Agents and Actions, 1987. PubMed 3630857.
- Wegmüller R, et al. Zinc absorption by young adults from supplemental zinc citrate is comparable with that from zinc gluconate and higher than from zinc oxide. Journal of Nutrition, 2014. PubMed 24259556.
- Great Britain nutrition and health claims register. gov.uk.
- NHS. Vitamins and minerals: others, including zinc and copper. nhs.uk.
- Retained Regulation (EU) No 1169/2011, Annex XIII, nutrient reference values. legislation.gov.uk.
- Sakai F, et al. Double-blind, placebo-controlled trial of zinc picolinate for taste disorders. Acta Oto-Laryngologica, 2002. PubMed 12132610.
- Samman S, Roberts DC. The effect of zinc supplements on plasma zinc and copper levels and the reported symptoms in healthy volunteers. Medical Journal of Australia, 1987. PubMed 3547053.
- NHS. Ciprofloxacin, and doxycycline, with other medicines and supplements. nhs.uk; nhs.uk.
- Lönnerdal B. Dietary factors influencing zinc absorption. Journal of Nutrition, 2000. PubMed 10801947.
This article is general information, not medical advice. Do not take more than 25 mg of zinc a day from supplements unless a doctor has advised it, and ask a pharmacist before combining zinc with any medicine.
