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Zinc
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In one pass Zinc hardly ever works alone: it is a helper (cofactor) for hundreds of enzymes, and immunity, wound healing, taste and smell, growth and testosterone production all lean on it.
Educational content, not medical advice — consult a clinician.
A floppy polypeptide Before zinc arrives, a zinc finger is a floppy chain of about 30 amino acids with no stable structure, unable to recognise DNA.
Thymus · T-cell academy T precursor cells from the bone marrow pass two selection gates in the thymus, positive and negative, before maturing and leaving, and this training is highly zinc-dependent.
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Chapter 1
Zinc from animal foods absorbs better
Zinc hardly ever works alone: it is a helper (cofactor) for hundreds of enzymes, and immunity, wound healing, taste and smell, growth and testosterone production all lean on it. The people most likely to run short are those who eat mainly plant foods for years (phytate grips the zinc), people who absorb food poorly, women who are pregnant or breastfeeding, and athletes who sweat heavily.
How much of the zinc you eat actually gets absorbed varies enormously: according to the NIH Office of Dietary Supplements (NIH ODS), anywhere from 5% to more than 50%, depending mainly on how much of the meal is plant food — that is, how much phytate it contains. That is why people who regularly eat oysters (see Oysters) and red meat (see Beef · see Lamb · see Pork) rarely run short, while vegans or people who live mainly on whole grains and legumes have zinc on the plate but get less of it into the body. Soaking beans, sprouting and fermenting all come down to breaking phytate apart.
How much of the zinc you eat actually gets absorbed varies enormously: according to the NIH Office of Dietary Supplements (NIH ODS), anywhere from 5% to more than 50%, depending mainly on how much of the meal is plant food — that is, how much phytate it contains. That is why people who regularly eat oysters (see Oysters) and red meat (see Beef · see Lamb · see Pork) rarely run short, while vegans or people who live mainly on whole grains and legumes have zinc on the plate but get less of it into the body. Soaking beans, sprouting and fermenting all come down to breaking phytate apart.
Numbers · Where zinc is, and how much gets in
The table below explains why people who regularly eat meat and seafood are usually not short of zinc.Zinc content (mg / 100 g):
Oysters 16.6 mg (Pacific oyster) – 39 mg (eastern oyster, raw). Cooking and canning concentrate it further as water is lost; a medium oyster weighs 60–80 g in the shell but has only 10–15 g of meat, so it takes a serving of about 6 (70–90 g of meat) to cover or exceed a day's need, not one (if you eat oysters raw, watch for bacterial contamination — see Oysters)Red meat (beef) ~5–7 mgPumpkin seeds ~7 mgCashews ~5.6 mgLamb ~5 mgLentils and chickpeas ~3 mg (but gripped by phytate)Oats (raw) ~4 mgYogurt ~1 mg
Recommended intake: the US Recommended Dietary Allowance () is 11 mg/day for adult men and 8 mg/day for adult women (11 in pregnancy, 12 while breastfeeding).
Where absorption differs: zinc in animal foods is mostly bound to protein and is released and absorbed easily; zinc in plant foods is held by phytate, and much less of it is absorbed. That is why the US Institute of Medicine (IOM) suggests that people on a strict vegetarian diet for the long term may need up to 50% more than the RDA (about 16 mg/day for men and 12 mg/day for women).
Traditional ways of removing phytate: soaking (legumes for the better part of a day), sprouting and fermenting (sourdough, natto, miso, Indian dosa) all activate the phytase enzyme that foods carry themselves, breaking phytate down so that zinc is absorbed more easily — which is why the zinc in sourdough is better absorbed than the zinc in ordinary white bread. Soaking beans, leavening dough and brewing sauces in traditional cooking are not only about flavor; they are also a kind of nutritional processing.
Myth · Does zinc raise testosterone?
Take zinc for testosterone and sexual performance is one of the most common, and most misleading, claims in the supplement market. Here is the evidence, point by point:The real part: zinc deficiency does lower testosterone in the blood. Prasad 1996 was a very small before-and-after study with no control group: when young men's zinc intake was restricted, their testosterone fell clearly; when marginally zinc-deficient older men were given zinc for 6 months, their testosterone rose from about 8 nmol/L to about 16 nmol/L. Possible mechanisms include zinc's roles in gonadotropin signaling and in the enzymes that make steroid hormones, a layer of evidence that comes mostly from animal and cell studies.
The overlooked caveat: those men were already short of zinc. In people with enough zinc, there is no evidence that taking more raises testosterone (Koehler 2009 and other studies saw no extra rise). The small studies behind zinc raises testosterone in athletes mostly had small samples, no blinding, short durations and no baseline zinc measurement. Taking 50–100 mg/day for the long term — far above the adult tolerable upper intake level of 40 mg — carries a more practical risk: blocking copper at the gut (the chapter on how too much zinc drains copper covers this).
Semen and male fertility: it is true that semen is rich in zinc, but the path from zinc eaten to zinc in semen to sperm quality is not a straight line, and clinical trials give inconsistent results.
In practice: if you really are short of zinc (symptoms, a low diet assessment, and a blood zinc test when needed), correcting it matters. For healthy adult men with enough zinc, supplements can only refill what is missing; they cannot push testosterone above where it already sits. To keep testosterone in the normal range, look first at whether you sleep 7 hours or more, at body fat, strength training, vitamin D, and whether you have been eating too little for a long time — all of these matter far more than zinc alone.
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Chapter 2
Phytate blocks zinc absorption
Zinc gets into the body through two doors: a transporter called ZIP4, on the side of the gut cell facing the gut, pulls zinc ions into the cell, and another called ZnT1, on the side facing the blood, passes them on into the bloodstream. When the body is short of zinc, ZIP4 increases, but only up to a ceiling. So the share of zinc absorbed ranges from 5% to more than 50% — even less predictable than iron.
The biggest source of that swing is phytate: it locks zinc into insoluble complexes, and a meal built mainly on whole grains and legumes often cuts zinc absorption substantially. An iron supplement swallowed together with a zinc supplement competes for absorption, and a large calcium pill may too; chronic diarrhea and inflammatory bowel disease () lose zinc outright. Protein in a meal helps a little more zinc from plant foods get in.
The biggest source of that swing is phytate: it locks zinc into insoluble complexes, and a meal built mainly on whole grains and legumes often cuts zinc absorption substantially. An iron supplement swallowed together with a zinc supplement competes for absorption, and a large calcium pill may too; chronic diarrhea and inflammatory bowel disease () lose zinc outright. Protein in a meal helps a little more zinc from plant foods get in.
Mechanism · How zinc is absorbed, and what blocks it
Active zinc absorption relies on two transporters: ZIP4, on the membrane at the top of the gut cell, pulls Zn²⁺ into the cell, and ZnT1, on the membrane at its base, moves Zn²⁺ out of the cell and into the blood. The amount of ZIP4 tracks the body's zinc status: it rises when zinc is low, but only up to a limit. According to the NIH Office of Dietary Supplements (NIH ODS), the share of zinc absorbed from food ranges from 5% to more than 50% — even less predictable than iron.Common inhibitors:
Phytate (inositol hexaphosphate, IP6): the biggest factor, locking zinc into insoluble complexes; it is present in staples such as cereals, corn and rice, and strongly reduces zinc absorption from mixed meals (Lönnerdal 2000). Diets built on whole grains and legumes often cut zinc absorption substantiallyIron supplements: taken at the same time as zinc supplements, they lower zinc absorption; NIH ODS refers to iron supplements of 25 mg or more. Iron added to fortified foods does not have this effectLarge doses of calcium (> 1 g at a meal): may also affect zinc absorption, though studies do not fully agreeChronic diarrhea and inflammatory bowel disease (): zinc is lost outright
Enhancers: protein in a meal generally helps zinc absorption (red meat in particular helps more zinc from plant foods in the same meal get in); amino acids such as histidine, and small molecules such as EDTA and citrate, bind zinc and help it be absorbed, which is why they are used in zinc supplements (Lönnerdal 2000).
Zinc deficiency worldwide: estimates based on the zinc and phytate in national food supplies, combined with rates of stunted growth in children, suggest that about 17% of the world's population may be zinc-deficient (NIH ODS). This is a risk estimate, not a count of people measured one by one; the risk is concentrated where cereals are the staple, little meat is eaten and soils are low in zinc (Southeast Asia, South Asia, the Middle East and sub-Saharan Africa). Zinc-deficient children grow poorly, have repeated diarrhea and fight infection poorly — a major public-health problem in many developing countries. Severe deficiency is rare in healthy adults in developed countries; people over 50, vegans and people with IBD are at higher risk.
In practice · Choosing and timing a zinc supplement
Zinc supplements are less forgiving about form and timing than vitamin D. A few key points:Forms:
Zinc citrate and zinc gluconate: in a study cited by the NIH Office of Dietary Supplements (NIH ODS), young adults absorbed the two about equally well, around 61%; zinc gluconate is also a common form in zinc lozengesZinc oxide: absorbed at about 50% in the same study — a little lower than the two above, but not barely absorbed; it is also a common ingredient in sunscreenZinc picolinate and zinc bisglycinate: often marketed as better absorbed and gentler on the gastrointestinal (GI) tract, but few studies have compared them directlyZinc sulfate: cheap, and more likely to irritate the stomach
Timing: on an empty stomach (1 hour before or 2 hours after a meal) absorption is best, but stomach upset is more likely; taken with food it is better tolerated, though somewhat less is absorbed. Keep it at least 2 hours apart from iron supplements, calcium supplements and high-fiber meals.
Dose: people who are not short of zinc do not need more than the recommended intake (11 mg/day for adult men, 8 mg/day for adult women); the dose and length of treatment for a deficiency should be set by a doctor. The adult tolerable upper intake level () is 40 mg/day (food plus supplements), not to be exceeded long term; for short-term lozenge use during a cold, see the chapter on immunity.
Copper: if you take close to the 40 mg upper limit every day for a long time, copper has to be considered: talk to a doctor first, and have blood copper checked if needed. There is no agreed fixed ratio for combining zinc and copper in supplements.
Chapter 3
Enzyme helper and protein scaffold
Zinc has two jobs. One is catalytic: it is a helper (cofactor) for hundreds of enzymes (often put at more than 300), from carbonic anhydrase, which helps regulate breathing and acid-base balance, and the antioxidant enzyme copper-zinc superoxide dismutase, to protein digestion, bone mineralization, DNA copying, alcohol metabolism and wound remodeling.
The other job is structural. The zinc finger is the most common way DNA-binding proteins fold: a single zinc ion is gripped by two cysteines and two histidines, folding a stretch of protein into a finger that slots into the major groove of DNA. Zinc-finger transcription factors are the largest family of transcription factors in humans.
When zinc runs mildly low, taste, skin, resistance to infection and wound healing are often affected together. The cause may not lie in the zinc fingers themselves (they hold their zinc very tightly); more likely, the small pool of zinc that each cell can draw on at short notice runs low first.
The other job is structural. The zinc finger is the most common way DNA-binding proteins fold: a single zinc ion is gripped by two cysteines and two histidines, folding a stretch of protein into a finger that slots into the major groove of DNA. Zinc-finger transcription factors are the largest family of transcription factors in humans.
When zinc runs mildly low, taste, skin, resistance to infection and wound healing are often affected together. The cause may not lie in the zinc fingers themselves (they hold their zinc very tightly); more likely, the small pool of zinc that each cell can draw on at short notice runs low first.
Mechanism · Zinc's two jobs: catalysis and structure
Zinc's work has two sides.Catalysis: it is a helper (cofactor) for more than 300 enzymes, including:
Carbonic anhydrase (CA): converts CO₂ to HCO₃⁻, taking part in breathing and acid-base balanceSuperoxide dismutase (Cu/Zn-SOD): antioxidant defenseCarboxypeptidase, trypsin and elastase: protein digestionAlkaline phosphatase: bone mineralizationDNA and RNA polymerases: copying and transcribing genesAlcohol dehydrogenase (ADH): breaking down alcoholMatrix metalloproteinases (MMPs): tissue remodeling and wound repair
Structure: the zinc finger is the most common folding pattern among DNA-binding proteins: a single Zn²⁺ is gripped by 2 cysteines and 2 histidines, folding a stretch of protein into a finger shape that slots into the major groove of DNA.
A commonly cited textbook estimate is that about 10% of human proteins bind zinc, and zinc-finger proteins are the largest group among them; transcription factors such as TFIIIA, Sp1 and Krüppel are classic zinc fingers. The receptors for estrogen, androgens, glucocorticoids and vitamin D (together called nuclear receptors) also rely on zinc to fold the part that reads DNA, but there the zinc is held by 4 cysteines, and the shape differs from a classic zinc finger. The p53 tumor-suppressor protein also needs a zinc ion to fold into a shape that can bind DNA.
What this means: zinc is not only a helper that lets enzymes work; it is also a structural part that gives shape to a large set of DNA-reading proteins. But be careful about the next step: the reduced taste, skin problems, repeated colds and slow wound healing seen with mild zinc deficiency are hard to blame directly on failing zinc fingers, because zinc fingers hold their zinc very tightly. Nutrition scientists explain it differently: zinc is a nutrient that supports growth and metabolism throughout the body, so a shortage does not break one function but slows many at once; each cell has a small pool of zinc it can draw on, and that pool is the first to run low when intake falls short (King 2011).
Mechanism · Zinc fingers and gene editing
The zinc finger (ZF) is one of the most important structures that proteins use to recognize DNA.Structure: 2 cysteines and 2 histidines together grip 1 Zn²⁺, holding up a finger-shaped fold of about 30 amino acids; the fingertip slots into the major groove of DNA and recognizes a specific stretch of 3 (sometimes 4) bases.
Biological significance: zinc-finger transcription factors are the largest family of transcription factors in humans and switch a great many genes on and off. The nuclear receptors (estrogen receptor ER, androgen receptor AR, glucocorticoid receptor GR, vitamin D receptor , vitamin A receptor RAR) also rely on zinc to fold the part that reads DNA, but there the zinc is held by 4 cysteines, and the shape is not the same as the classic zinc finger above.
Zinc fingers and gene editing (2010s): joining zinc fingers designed to order to a cutting enzyme called FokI produces a zinc-finger nuclease (ZFN), a precise gene-editing tool that predates CRISPR. ZFNs have been tested in clinical trials — for example, editing the CCR5 gene in T cells to make them resist HIV — but none has become an approved therapy. CRISPR, being far easier to design, later took over most of these uses; ZFNs are still being studied in a few settings.
What is seen in the clinic: severe zinc deficiency brings a whole cluster of problems at once — underactive sex glands, stunted growth, skin problems and poor resistance to infection. That is why acrodermatitis enteropathica (a mutation in the gene for the zinc transporter ZIP4 that stops zinc being absorbed) looks so dramatic. Zinc is involved in so many steps that the cluster is hard to pin on any single pathway: effects on nuclear receptors and zinc fingers are one plausible explanation, but it has not been directly shown.
Chapter 4
Training immune T cells
The thymus is the training school for T cells (a type of white blood cell that recognizes and clears infected cells). Thymulin, a hormone made by the thymus, works only when it binds a zinc ion, and several enzymes in the signals that switch T cells on also need zinc. In animal experiments, zinc deficiency makes the thymus shrink quickly and cuts the output of T cells; in people, those short of zinc are more prone to repeated infections.
Zinc lozenges for colds are a separate matter: the free zinc released as a lozenge dissolves in the mouth acts mainly in the nose and throat, not by raising zinc levels throughout the body. In the 2024 Cochrane review (Nault 2024), treatment with zinc shortened colds by about 2.4 days on average, but the certainty of the evidence is low; taken to prevent colds, it made little or no difference.
Zinc lozenges for colds are a separate matter: the free zinc released as a lozenge dissolves in the mouth acts mainly in the nose and throat, not by raising zinc levels throughout the body. In the 2024 Cochrane review (Nault 2024), treatment with zinc shortened colds by about 2.4 days on average, but the certainty of the evidence is low; taken to prevent colds, it made little or no difference.
Evidence · The thymus, zinc and cold lozenges
The thymus is the training school for T cells. T-cell precursors go through positive and negative selection there: those that can recognize the body's own MHC molecules (the display stands on cell surfaces that present antigens) are kept, and those that react too strongly against the body's own tissues are removed, before the survivors leave as mature T cells.The thymus depends heavily on zinc. Thymulin is a peptide hormone released by the cells lining the thymus; it becomes active only when it binds one Zn²⁺, and it is a key signal for T-cell development. Several phosphatases and kinases in the T-cell receptor (TCR) signaling pathway depend on zinc, as does interleukin-2 (IL-2) signaling, which T cells need to become activated.
What happens with zinc deficiency: in animal experiments, the thymus shrinks noticeably within a few weeks of zinc deficiency, T-cell output falls, the balance between the two T-cell types, CD4 and CD8, is disturbed, and antibody responses weaken. In people, zinc-deficient children are more prone to repeated infections. It has been proposed that part of the age-related decline of the thymus (immunosenescence) comes from long-term low zinc, but this is still a hypothesis.
The evidence on zinc lozenges for colds: the current Cochrane review is Nault 2024. Treatment with zinc shortened illness by about 2.4 days on average (95% 0.5–4.2), but the studies differed enormously (I² = 97%, meaning the results were highly inconsistent), and the certainty of the evidence is low; for prevention, zinc made little or no difference. Looking only at the three randomized trials of zinc acetate lozenges in which form, dose and timing were all right (Hemilä 2016, an individual-patient-data , N = 199), colds were about 2.7 days shorter than the 7-day average. Hemilä and colleagues consider that starting after 24 hours, or taking too low a dose, clearly weakens the effect.
The widely repeated claim that zinc cuts colds by 33% comes from a line of reviews by Singh and Das: that Cochrane review was withdrawn in 2015 (the withdrawn version is literally titled WITHDRAWN), and the companion 2014 JAMA paper by Das and Singh received a retraction notice in 2016. That number should not be used again.
Form: almost all the trials that worked used zinc acetate or zinc gluconate lozenges that were sucked, not swallowed. By the logic of acting locally, swallowed zinc tablets should not help, but this has not been compared directly.
So the effect of zinc lozenges is real but limited, and the certainty of the evidence is not high: they are not a way to prevent colds, and they may be worthwhile only if started within 24 hours of the first acute symptoms.
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In practice · Getting zinc lozenges right
There is a signal from randomized trials that zinc can shorten colds, but Cochrane rates it as low certainty. For it to have a chance of working, the form, dose and timing all have to be right.What the trials did:
Form: zinc acetate or zinc gluconate lozenges, dissolved slowly in the mouth, not swallowedDose: 75–100 mg of elemental zinc a day, taken in portions (one lozenge every 2–3 hours, each about 13–23 mg); the three zinc acetate trials pooled by Hemilä used 80–92 mg/dayTiming: start within 24 hours of the first symptoms and continue for 5–7 days, until symptoms easeMechanism (a hypothesis): free zinc ions released by the lozenge may, in the nose and throat, interfere with rhinovirus binding to ICAM-1 (the receptor the virus attaches to in order to enter cells), and may also damp down local inflammation
What may not work, or works less well:
Swallowing zinc tablets: by the logic of acting locally, it should not help; it has not been compared directlyLozenges made with citric acid or tartaric acid: these ingredients grab zinc ions, so by the same logic less free zinc is released (Hemilä's view; again, no trial has compared them directly)Taking zinc every day to prevent colds: Cochrane concludes it makes little or no differenceStarting more than 24 hours after symptoms appear: by the mechanism, the step it could block has already passedToo low a dose (< 75 mg/day): the local concentration may not be high enough
The current Cochrane review is Nault 2024 (not Singh & Das, whose line was withdrawn): treatment with zinc shortens illness by about 2.4 days on average, at low certainty; the three zinc acetate lozenge trials on their own give about 2.7 days (Hemilä 2016). Nault 2024 also found that people treated with zinc had more non-serious side effects, such as nausea and a bad taste in the mouth.
Safety notes: using high-dose zinc for more than 7 days in a row lowers copper absorption and can cause a metallic taste and mouth discomfort; zinc nasal sprays can cause permanent loss of smell, and the US FDA has issued a warning; children who suck lozenges may swallow them, so ask a pediatrician before using them.
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Chapter 5
Wound healing and skin
The skin is one of the body's largest stores of zinc, holding about 5% of the total, and both keratinocytes in the outer skin and fibroblasts in the deeper layer depend on it. Wound healing runs through four stages — stopping the bleeding, inflammation, rebuilding and remodeling — and zinc is present at every one: the polymerases that copy DNA need zinc, and the whole family of matrix metalloproteinases (MMPs), which break down the old tissue scaffolding during remodeling, depends on it.
With zinc deficiency, wounds heal slowly, and dermatitis tends to appear around the face, the genital area and the fingertips; the classic acrodermatitis enteropathica is caused by a mutation in the gene for the zinc transporter ZIP4 that stops zinc being absorbed. In people who really are short of zinc, correcting it helps large wounds and burns heal; for people who are not short, the evidence on zinc creams or high-dose zinc pills for acne and eczema is inconsistent.
With zinc deficiency, wounds heal slowly, and dermatitis tends to appear around the face, the genital area and the fingertips; the classic acrodermatitis enteropathica is caused by a mutation in the gene for the zinc transporter ZIP4 that stops zinc being absorbed. In people who really are short of zinc, correcting it helps large wounds and burns heal; for people who are not short, the evidence on zinc creams or high-dose zinc pills for acne and eczema is inconsistent.
Mechanism · Zinc in the four stages of healing
The skin is one of the body's largest stores of zinc (about 5% of the total). Keratinocytes in the outer skin and fibroblasts in the deeper layer need zinc throughout their work.Zinc takes part in all four stages of wound healing:
1. Stopping the bleeding: zinc helps regulate platelet clumping and clotting
2. Inflammation: neutrophils and macrophages clear debris and bacteria, and the function of these scavenger cells also depends on zinc status
3. Rebuilding: rapid cell division (DNA polymerase needs zinc), collagen production (prolyl hydroxylase needs vitamin C, but zinc helps regulate the related signals) and growth of new blood vessels
4. Remodeling: matrix metalloproteinases (MMPs) reshape the scaffolding between cells, and the whole MMP family depends on zinc
Common signs of zinc deficiency:
Slow wound healing: people with diabetic foot ulcers or chronic pressure sores often have low zincDermatitis (face, genital area, limbs): the classic acrodermatitis enteropathica is a severe failure to absorb zinc caused by a mutation in the ZIP4 geneAcne: people with acne have lower blood zinc on average, but whether this is a cause or a consequence is unclearEczema that keeps coming backHair loss (telogen effluvium): the cells in the hair follicle that grow hair divide more slowly
Clinical evidence: correcting zinc deficiency after large wounds or burns improves the speed of healing, with the evidence coming mainly from patients who were truly deficient. For people who are not short of zinc, the evidence on zinc creams or high-dose zinc pills for acne and eczema is inconsistent: correcting a shortfall helps, while taking too much is useless or even harmful (the chapter on how too much zinc drains copper covers this).
Clinical · How good is the evidence on zinc for acne
Take zinc for acne is a marketing pitch. Here is what the evidence says:Observational evidence: several studies have found that people with acne have lower plasma zinc on average, and some see fewer spots after taking zinc. These are associations; they do not show that low zinc causes acne.
Randomized trials: Dreno 2001 was a multicenter, double-blind randomized trial that gave people with inflammatory acne either 30 mg/day of elemental zinc (as zinc gluconate) or the antibiotic minocycline for 3 months: both groups improved, but minocycline was clearly better. Some small placebo-controlled trials have also seen some improvement with zinc (reviewed by Cervantes 2018). The forms usually used are zinc gluconate or zinc sulfate at 30 mg of elemental zinc by mouth, or 1–2% zinc preparations on the skin, for 8–12 weeks. Possible mechanisms are damping inflammation, suppressing the acne bacterium (now called Cutibacterium acnes, formerly Propionibacterium acnes) and regulating skin oil.
In practice:
For mild to moderate inflammatory acne, when oral antibiotics are not tolerated or not wanted, zinc can be an add-on, tried for 8–12 weeksFor severe or cystic acne, isotretinoin is the standard treatment, and zinc cannot replace itTopical vitamin A derivatives (tretinoin, adapalene) plus benzoyl peroxide remain the foundation of treatmentTaking more than 40 mg/day on your own for a long time means watching for copper deficiency
For use on the skin, a combination of erythromycin and zinc (Zineryt) is licensed in Europe.
Overall: zinc is not a miracle cure for acne, but a cheap, low-risk add-on with fairly weak evidence behind it.
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Chapter 6
Too much zinc drains copper
Taking too much zinc drains copper. High doses of zinc increase metallothionein (a small protein that grabs metals) in gut cells, and it holds copper even more tightly than zinc; the copper stays trapped in the gut cells and is lost in the stool when those cells are shed. Over time, the result is copper deficiency.
Copper deficiency is often mistaken for something else: the anemia looks like iron deficiency, the nerve damage looks like vitamin B12 deficiency, and there can also be low white blood cells and osteoporosis. The tolerable upper intake level () of zinc for adults is 40 mg a day, not to be exceeded long term; a few days of zinc lozenges during a cold can go higher. Wilson disease turns the same mechanism into a treatment.
Copper deficiency is often mistaken for something else: the anemia looks like iron deficiency, the nerve damage looks like vitamin B12 deficiency, and there can also be low white blood cells and osteoporosis. The tolerable upper intake level () of zinc for adults is 40 mg a day, not to be exceeded long term; a few days of zinc lozenges during a cold can go higher. Wilson disease turns the same mechanism into a treatment.
Safety · How too much zinc blocks copper
A classic supplement mistake is if zinc is good, take more. Long-term high-dose zinc steals copper.Mechanism: high zinc increases metallothionein (MT) in gut cells; MT binds copper even more strongly than zinc and grabs it first; copper-loaded MT is lost in the stool as gut-lining cells are naturally shed, so the gut ends up keeping copper out. Over time, the result is copper deficiency.
The symptoms of copper deficiency are often mistaken for other problems:
Anemia (copper helps release iron for use): looks very like iron deficiencyLow white blood cells (neutrophils depend on copper)Nerve damage: spinal-cord degeneration, abnormal sensations and unsteady walking that resemble vitamin B12 deficiencyOsteoporosis (lysyl oxidase contains copper and helps cross-link collagen)
A course often seen in case reports: someone takes several times the every day for a long time to improve their sense of taste, and after some months develops severe anemia and nerve symptoms. Doctors first treat it as B12 deficiency, without success; only then do tests show very low copper, and after the zinc is stopped and copper given, the person gradually recovers. The NIH Office of Dietary Supplements (NIH ODS) also describes another source: years of heavy use of zinc-containing denture adhesive, which likewise caused copper deficiency and nerve disease.
Safe dose:
The adult tolerable upper intake level (UL) is 40 mg/day (food plus supplements), not to be exceeded long termA few days of zinc lozenges during a cold (75–100 mg/day) is fine; NIH ODS also notes that the UL does not apply to zinc given as treatment under a doctor's supervisionIf you take close to 40 mg every day for a long time, copper has to be considered: talk to a doctor first, and have blood copper checked if needed; there is no agreed fixed ratio for combining zinc and copperMost people get enough from food and do not need supplements
This is one of the few supplements with a clear dose boundary: too much really does cause harm.
Clinical · Why zinc treats Wilson disease
Too much zinc harms copper becomes a treatment in Wilson disease.Wilson disease: a mutation in the ATP7B gene leaves the liver unable to pass copper into bile, so copper builds up in the liver, brain and cornea and can cause disability or death. The copper story covers it in more detail.
Zinc as a Wilson disease drug: zinc acetate (brand name Galzin) or zinc gluconate, 50 mg of elemental zinc per dose, three times a day. The mechanism is exactly the one above: making gut cells produce more metallothionein, which keeps copper from food out; copper that has already built up is gradually excreted in bile (even though that route is impaired), and the body's copper pool slowly falls. For maintenance treatment, zinc has fewer side effects than chelating drugs (such as penicillamine), but it works slowly, taking 4–6 months.
The same physical mechanism that causes copper deficiency as a side effect in ordinary people is the treatment in Wilson patients.
The lesson: poison and medicine often trade places depending on dose and the disease in the background — one of the most basic facts in pharmacology, and one of the most often forgotten. Do not reason that because Wilson patients take 150 mg of zinc a day, you can too: you do not have Wilson disease, and for you the same dose is real toxicity.
References · 6
- National Institutes of Health, Office of Dietary Supplements. (2022). Zinc — Fact Sheet for Health Professionals. ods.od.nih.gov/factsheets/Zinc-HealthProfessional
- Lönnerdal, B. (2000). Dietary factors influencing zinc absorption. Journal of Nutrition, 130(5S Suppl), 1378S–1383S. 10.1093/jn/130.5.1378S
- U.S. Department of Agriculture, Agricultural Research Service. (2019). FoodData Central: Mollusks, oyster, eastern, wild, raw (SR Legacy, FDC ID 171978). Per 100 g raw: 51 kcal, 5.71 g protein, 1.71 g fat, 39.3 mg zinc, 4.61 mg iron, 2.86 mg copper, 19.7 µg selenium, 8.75 µg vitamin B12, 40 mg cholesterol, 85 mg sodium, EPA+DHA 0.31 g. Pacific oyster (FDC ID 174219) — the species farmed most heavily in China — differs materially: 81 kcal, 9.45 g protein, 16.6 mg zinc, 77.0 µg selenium, 50 mg cholesterol. Cooking and canning concentrate zinc (eastern, cooked dry heat FDC ID 175171: 61 mg; canned FDC ID 171981: 91 mg). fdc.nal.usda.gov
- Prasad, A. S., Mantzoros, C. S., Beck, F. W., Hess, J. W., & Brewer, G. J. (1996). Zinc status and serum testosterone levels of healthy adults. Nutrition, 12(5), 344-348. Small before-after study in two groups: experimental dietary zinc restriction in young men lowered serum testosterone, and zinc repletion in marginally zinc-deficient older men raised it. Very small samples and no control arm — it establishes that zinc is required for testosterone synthesis, not that extra zinc raises testosterone in zinc-replete people. 10.1016/s0899-9007(96)80058-x
- Institute of Medicine. (2001). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academies Press. www.ncbi.nlm.nih.gov/books/NBK222310
- King, J. C. (2011). Zinc: an essential but elusive nutrient. American Journal of Clinical Nutrition, 94(2), 679S–684S. 10.3945/ajcn.110.005744