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Vitamins Information (Home) > Side Effects > Zinc Zinc Side EffectsZinc intake in excess of 300 mg per day has been reported to impair immune function. Some people report that zinc lozenges lead to stomach ache, nausea, mouth irritation, and a bad taste. One source reports that gastrointestinal upset, metallic taste in the mouth, blood in the urine, and lethargy can occur from chronic oral zinc supplementation over 150 mg per day, but those claims are unsubstantiated. In topical form, zinc has no known side effects when used as recommended. However, using zinc nasal spray has been reported to cause severe or complete loss of smell function in at least ten people. In some of those cases, the loss of smell was long-lasting or permanent. Preliminary research had suggested that people with Alzheimer’s disease should avoid zinc supplements. More recently, preliminary evidence in four patients actually showed improved mental function with zinc supplementation. In a convincing review of zinc/Alzheimer’s disease research, perhaps the most respected zinc researcher in the world concluded that zinc does not cause or exacerbate Alzheimer’s disease symptoms. Zinc inhibits copper absorption. Copper deficiency can result in anemia, lower levels of HDL (“good”) cholesterol, or cardiac arrhythmias. Copper intake should be increased if zinc supplementation continues for more than a few days (except for people with Wilson’s disease). Some sources recommend a 10:1 ratio of zinc to copper. Evidence suggests that no more that 2 mg of copper per day is needed to prevent zinc-induced copper deficiency. Many zinc supplements include copper in the formulation to prevent zinc-induced copper deficiency. Zinc-induced copper deficiency has been reported to cause reversible anemia and suppression of bone marrow. Marginal zinc deficiency may be a contributing factor in some cases of anemia. In a study of women with normocytic anemia (i.e., their red blood cells were of normal size) and low total iron-binding capacity (a blood test often used to assess the cause of anemia), combined iron and zinc supplementation significantly improved the anemia, whereas iron or zinc supplemented alone had only slight effects. Supplementation with zinc, or zinc and iron together, has been found to improve vitamin A status among children at high risk for deficiency of the three nutrients. Zinc competes for absorption with copper, iron, calcium, and magnesium. A multimineral supplement will help prevent mineral imbalances that can result from taking high amounts of zinc for extended periods of time. N-acetyl cysteine (NAC) may increase urinary excretion of zinc. Long-term users of NAC may consider adding supplements of zinc and copper. Certain medicines may interact with zinc. Refer to drug interactions for a list of those medicines.
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