Zinc is a mineral found in food and taken as a supplement. It can help with cold symptoms and diarrhea. Zinc is available in a variety of products, including oral (by mouth) and topical (applied to the skin). Possible side effects from zinc supplements include gastrointestinal (GI) side effects, headache, dizziness, numbness, weakness, and abnormal levels on blood tests.
Zinc doses larger than 1-2 grams can raise your risk for unwanted side effects.
Large doses of zinc can cause digestive side effects like abdominal cramps, nausea, vomiting, and diarrhea. These side effects are likely to happen within three to 10 hours of swallowing a zinc supplement. Zinc may affect the bacteria and environment (microbiome) of the gut, which increases your risk for GI-related side effects.
In one study, 84% of women and 18% of men reported nausea, abdominal cramps, and loss of appetite after taking 50 milligrams of elemental zinc three times a day for six weeks. The difference between women and men may be due to women weighing less than men on average.
Zinc may also cause diarrhea, even though the mineral is sometimes used to treat diarrhea. One study found that zinc raises the risk of diarrhea in children taking large zinc doses. However, other studies found no difference in diarrhea risk. The risk for diarrhea is also higher when taking zinc with an iron supplement.
High doses of zinc can cause headache or dizziness. These symptoms are more common after taking a large dose of zinc. If using zinc as prescribed, the chance for these issues is low.
Lowering your zinc dosage and overall intake should help resolve these symptoms.
High doses of zinc can lead to neurological (brain and nerve) problems, like numbness and weakness. This is seen in people who are chronically exposed to high doses of zinc.
Some research suggests this may be caused by low copper levels. Low copper causes weakness by lowering energy production and impairing iron and healthy blood cells throughout the body. This prevents your body from sending enough oxygen to your muscle tissues, which can lead to weakness.
These side effects are rare. If you begin experiencing numbness or weakness, see a healthcare provider immediately.
Consuming too much zinc can affect iron, copper, and cholesterol levels in your body. When your body absorbs zinc, it binds to a protein that affects minerals (like copper and iron) in your body. With high zinc levels, your body makes more of these proteins to get rid of the extra zinc. However, this then lowers the availability of minerals like copper and iron.
Low copper levels can cause anemia (low red blood cell count), high cholesterol, increased risk of infection, and bone disease like osteoporosis.
To avoid any zinc-related side effects, do not take more than the recommended dose of zinc. The recommended dietary allowance (RDA) for zinc is as follows:
- Adult men: 11 milligrams
- Adult women: 8 milligrams
- People who are pregnant: 11 milligrams
- People who are lactating: 12 milligrams
The tolerable upper intake level of zinc in adults is 40 milligrams.
If you notice gastrointestinal side effects when you take zinc, consider taking the supplement with food. However, absorption is usually best when taken on an empty stomach.
Talk with a healthcare provider if you have questions related to zinc supplements and side effects.
