Zinc

What side effects can zinc cause?

Too much zinc can cause nausea, dizziness, headaches, stomach upset, vomiting and loss of appetite. 1

In cold-treatment trials, people taking zinc reported more non-serious side effects than people on placebo. In the FAZST fertility trial, abdominal pain, nausea and vomiting were more common with 30 mg zinc plus folic acid. 2 3

How does zinc affect copper?

Taken for weeks, 50 mg zinc a day or more can block copper absorption and lead to low copper status. It can also weaken immune function and lower HDL cholesterol. Food alone rarely provides this much zinc. 1

Heavy, long-term use of zinc-containing denture creams has caused copper deficiency with neurological symptoms, such as loss of balance and spinal cord damage, and anemia. 1

The US upper limits for zinc are based on the amount that affects copper status. The AREDS eye formula adds 2 mg copper to its 80 mg zinc. Very high doses, around 142 mg a day, may also disturb magnesium balance. 1

How much zinc is too much?

Upper limits apply to total intake from food and supplements over the long term. The US and EU set different values. The US limits do not apply to people receiving zinc for medical treatment under a doctor's care. 1 4

Doses used in some studies, such as 45 to 276 mg a day in short cold trials or 80 mg a day in the AREDS trial, exceed both limits. They describe the experiment, not a general intake. 1 2

In Germany, the BfR recommends no more than 6.5 mg zinc per daily dose of a supplement, with a note on products above 3.5 mg to avoid other zinc supplements. This is a recommendation; there are no binding legal maximum levels for supplements. 5 6

Which medicines interact with zinc?

NIH ODS advises people who take these or other medicines regularly to discuss their zinc status with their healthcare provider. 1

Can nasal zinc cause loss of smell?

Case series have described severe loss of smell after zinc gluconate gel was applied inside the nose. In one series of 17 patients, people reported sniffing the gel deeply, an immediate burning sensation, and loss of smell within 48 hours. Another report found that the loss appeared long-lasting or permanent in some cases. 7 8

Case series cannot show how often this happens. The reports concern products sprayed or applied in the nose, not lozenges or tablets. 7 8

Who should be careful with zinc supplements?

Needs rise in pregnancy and breastfeeding, but the adult upper limit stays the same. People with macular degeneration are advised to discuss zinc intake and the AREDS formulations with their doctor, and people on regular medication to review their zinc status with their healthcare provider. 1

People with inflammatory bowel disease, celiac disease, alcohol use disorder or a history of bariatric surgery are more likely to be low in zinc. A clinician can judge whether a deficiency is present, since a single blood test has limits. 1

How is zinc regulated in Germany and the EU?

In the EU, supplements may carry only authorized health claims for zinc, such as contributing to normal immune function or the maintenance of normal skin, hair and nails; 18 such claims are approved. In Germany, zinc medicines are sold only in pharmacies, and higher doses (from 25 mg per day) need a prescription. 6