Zinc is an essential mineral involved in more than 100 chemical reactions in our body. It is necessary for growth, DNA synthesis, and taste recognition, and for wound healing, reproduction, and immune function to occur smoothly.
The upper limit of zinc intake for adults is 40 mg per day. The upper intake limit refers to the maximum nutrient intake level that does not show any harmful effects on the human body.
Foods rich in zinc include red meat, poultry, seafood, whole grains, and fortified cereals. Oysters contain the highest amount, up to 673% of the recommended daily intake. Although some foods may contain much higher than the upper limit, there have been no reported cases of zinc poisoning due to zinc found naturally in foods.
However, zinc poisoning can occur if you accidentally swallow a nutritional supplement or an object that contains zinc. The US health information media ‘Healthline’ introduced the symptoms that can occur when zinc is overdose.
1. Nausea and Vomiting
Nausea and vomiting are common side effects of zinc poisoning.
A 2012 review of 17 studies of the effectiveness of zinc supplementation for the treatment of colds found that although zinc may reduce the duration of colds, side effects are common. Participants who took zinc were 64% more likely to experience nausea than the control group.
2. Abdominal pain and diarrhea
Abdominal pain and diarrhea are usually accompanied by nausea and vomiting.
A review published in 2021 reported that about 40% of participants reported abdominal pain and diarrhea. In less common cases, bowel irritation or gastrointestinal bleeding may also occur. There is a case of experiencing intestinal bleeding after taking 220 mg of zinc sulfate twice a day to treat acne.
Although not found in nutritional supplements, zinc chloride, which is present in adhesives, cleaning chemicals, and wood finishes, can be poisoned if accidentally ingested.
3. Flu-like symptoms
If you consume more zinc than the upper limit, symptoms similar to those of having the flu may appear, such as fever, chills, cough, headache, and fatigue. Diagnosing whether you have zinc poisoning can be difficult because the causes of these symptoms are numerous, including other mineral poisoning. Therefore, it is imperative that you tell your doctor if you are taking zinc supplements.
4. Lowering ‘good’ HDL cholesterol
High-density lipoprotein (HDL) cholesterol, also called good cholesterol, lowers the risk of heart disease and prevents plaque buildup in the arteries. The recommended level for adults is 40 mg/dL or higher, with lower levels increasing the risk of heart disease.
According to a meta-analysis published in 2015, about 40 mg of zinc per day lowered LDL (low-density lipoprotein) cholesterol by 11.25 mg/dl and significantly increased HDL cholesterol levels.
5. Change in taste
Zinc plays an important role in taste. Zinc deficiency can lead to hypogeusia, a taste disorder, and can cause changes in taste, such as a bad taste or metallic taste in the mouth when taken in excess of recommended levels. These symptoms have been reported in studies investigating common cold medicines or liquid nutritional supplements.
6. Copper deficiency
Zinc and copper are absorbed in the small intestine. Therefore, if zinc is taken in excess of the upper limit, copper may not be absorbed well, and a deficiency may occur over time. Copper contributes to the formation of red blood cells by helping iron absorption and metabolism, and is an essential mineral involved in the formation of white blood cells. Therefore, if you are taking supplements for copper deficiency, avoid taking zinc together.
7. Frequent infections
Because zinc plays an important role in immune function, a deficiency can affect its function. Conversely, taking too much zinc puts you at risk of suppressing your immune response.
There is a study showing that the function of T cells, a type of red blood cells, decreases when zinc is excessive. T cells play an important role in the immune response by attacking and eliminating harmful pathogens.