Zinc Toxicity, Copper Deficiency and Upper Limits

If someone has swallowed a lot of zinc

If a child or adult has swallowed many zinc tablets or an unknown amount, call Poison Help at 1-800-222-1222 (US) or 911 if the person is collapsed, confused or struggling to breathe. Other countries: Poison Help by Country and Poisoning: What to Do First. Do not wait for symptoms.

The short answer

A single large dose of zinc can cause headache, nausea, vomiting, diarrhea and stomach discomfort. [1] The slower problem is long-term high intake, which interferes with copper uptake, so many toxic effects of zinc are in fact due to copper deficiency. [2] Evidence labels: established mechanism and case reports for the copper effect; evidence of harm at high amounts for stomach upset. These are not claims that normal food amounts are unsafe.

How zinc lowers copper

Zinc and copper compete for absorption in the gut. High zinc raises a binding protein called metallothionein, which holds copper tightly, and the bound copper is lost in the stool. [2] Reviews describe anemia, low white cells (neutropenia) and neurologic symptoms. [1] A case report of an 81-year-old taking zinc for macular degeneration describes low blood counts and notes a delay of about 12 months between first symptoms and diagnosis. [3] Read the symptom side in Copper Deficiency: Causes, Symptoms and Who Is at Risk.

Official upper limits

An upper limit (UL) is the highest daily intake not expected to cause harm in almost everyone. EFSA defines it as total chronic daily intake from all dietary sources. [4] Figures are for elemental zinc in mg a day.

The limits differ by country, and the NHS figure covers supplements only. A limit is not a target.

Where excess zinc can come from

• Supplements and "immune" products. Labels may list the compound weight, not elemental zinc: zinc gluconate is about 14.3% elemental zinc and zinc oxide about 80.3%. [1] Check the "elemental" line (Zinc Forms Compared). Combination products can add up.
• Denture adhesive. In a case series of four people with nerve problems, low copper and high zinc, each used very large amounts of denture cream; the creams contained about 17,000 to 34,000 micrograms of zinc per gram. [7] Serum zinc improved after use stopped, and copper supplementation brought mild neurologic improvement in two. [7] A review advises following the package instructions and not using more than recommended. [1] Talk to a dentist or pharmacist if you use a lot.
• Fumes and dust. Welding, mining and smelting work can expose people to inhaled zinc. [1]
• Nasal products. See Zinc Nasal Sprays and Gels and Loss of Smell.

What study amounts show

In a study of 47 healthy volunteers, 84% of women and 18% of men reported nausea, loss of appetite or cramps after 50 mg elemental zinc three times a day for six weeks. [1] That is a study amount, not advice.

Who needs extra care

• Children and pregnancy: the limits above are lower for children; ask before giving zinc to a child, and see Pregnancy & Breastfeeding.
• Wilson disease: zinc is one treatment for copper build-up and needs monitoring by the treating team. [1]
• Medicines: zinc taken with quinolone or tetracycline antibiotics can interfere with how well the antibiotic works. [1] Ask a pharmacist; see Medication Interactions.
• Kidney, liver and surgery: zinc toxicity in kidney or liver disease, or bleeding risk before surgery, is not described in the sources we read. Tell your surgeon and clinician about every supplement. Quality varies: quality testing.

More: Zinc, Copper, Mineral Toxicity.