Can too much zinc cause copper deficiency?

Why the upper limit exists

The US upper limit for zinc, 40 mg a day for adults, is based on the amount that harms copper status.^[1] Taken for weeks, 50 mg or more a day can interfere with copper absorption, lower immune function and lower HDL cholesterol.^[1] Food alone rarely gives this much zinc.^[1]

High doses can also cause nausea, dizziness, headaches, stomach upset, vomiting and loss of appetite.^[1] Very high doses, 142 mg a day, may also upset the balance of magnesium.^[1]

The US upper limits for children are lower. They are 4 mg a day up to 6 months, 5 mg at 7 to 12 months and 7 mg at 1 to 3 years. For older children it is 12 mg at 4 to 8 years, 23 mg at 9 to 13 years and 34 mg at 14 to 18 years.^[1] EFSA, the EU food safety authority, sets 25 mg a day for adults, including in pregnancy and breastfeeding, and 7 to 22 mg for children aged 1 to 17.^[3]

What case reports show

A 2026 systematic review collected 37 published cases of blood problems caused by zinc, from 1972 to 2025:^[2]

• The zinc came most often from supplements, denture creams and swallowed coins.^[2]
• The doses ranged from about 50 mg to more than 1,500 mg a day, taken for weeks to years.^[2]
• Nearly every person had anemia, most often with low white blood cell counts. All had low copper in the blood.^[2]
• Doctors often first mistook the bone marrow changes for myelodysplastic syndrome, a bone marrow disease.^[2]

In most cases, blood counts recovered within weeks to months after people stopped zinc and took copper. Nerve symptoms improved more slowly and sometimes not fully.^[2] The authors advise doctors to ask about zinc intake and to check copper in people with anemia or low blood counts that have no clear cause.^[2]

Denture creams

Some denture creams contain 17 to 34 mg of zinc per gram. Used as directed, 0.5 to 1.5 g a day, they are not a concern.^[1] Zinc toxicity, with copper deficiency and nerve disease, was reported in people who used 70 g or more of cream a week for several years. Many denture creams no longer contain zinc.^[1]

Who should be careful

The AREDS eye formula contains 80 mg of zinc and adds 2 mg of copper.^[1] In cold trials, zinc gluconate lozenges gave 45 to 276 mg of zinc a day for up to 21 days.^[4] The US upper limits do not apply to people who take zinc as a treatment, but these people should be under a doctor's care.^[1] Ask a doctor or pharmacist before taking more than 40 mg a day.^[1]