Who is likely to be deficient?
Zinc deficiencies are quite common in people living in poor countries. Phytate, a substance
found in unleavened bread (pita, matzos, and some crackers) significantly reduces absorption
of zinc, increasing the chance of zinc deficiency. However, phytate-induced deficiency of zinc
appears to be a significant problem only for people already consuming marginally low amounts
of zinc.
Even in developed countries, low-income
pregnant women and pregnant teenagers are at risk for marginal zinc deficiencies.
Supplementing with 25–30 mg per day improves pregnancy outcome in these
groups.1 2
People with liver cirrhosis appear to be
commonly deficient in zinc.3 This deficiency may be due to cirrhosis-related zinc
malabsorption.4
People with Down’s syndrome are also commonly deficient in zinc.5 Giving
zinc supplements to children with Down’s syndrome has been reported to improve impaired
immunity6 and thyroid function,7 though optimal intake of zinc for
people with Down’s syndrome remains unclear.
Children with alopecia areata (patchy areas of hair loss) have been reported to be
deficient in zinc.8 9
The average diet frequently provides less than the Recommended Dietary Allowance for zinc,
particularly in vegetarians. To what extent
(if any) these small deficits in zinc intake create clinical problems remains unclear.
Nonetheless, a low-potency supplement (15 mg per day) can fill in dietary gaps. Zinc
deficiencies are more common in alcoholics and
people with sickle cell anemia, malabsorption problems, and chronic kidney
disease.10
Are there any side effects or interactions?
Zinc intake in excess of 300 mg per day has been reported to impair immune function.11 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,12
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.13
Preliminary research had suggested that people with Alzheimer’s disease should avoid zinc
supplements.14 More recently, preliminary evidence in four patients actually showed
improved mental function with zinc supplementation.15 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.16
Zinc inhibits copper absorption. Copper
deficiency can result in anemia, lower levels of HDL (“good”) cholesterol, neurological disorders, and cardiac arrhythmias.17 18
19 Copper intake should be increased if zinc supplementation continues for more than a
few days (except for people with Wilson’s
disease).20 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.21 In addition, there are case reports of neurologic
abnormalities due to copper deficiency occurring in people who had been using large amounts of
certain widely available denture creams that contained high concentrations of
zinc.22
In a study of elderly people with macular
degeneration, supplementation with 80 mg of zinc per day for an average of about 6 years
increased by about 50% the incidence of hospitalizations due to genitourinary causes (such as
urinary tract infections, kidney stones, and urinary retention).23 In that study,
copper was also given, but in a form that cannot be absorbed by humans (cupric oxide). The
reported adverse effect of zinc may have been due in large part to zinc-induced copper
deficiency, which could be prevented by taking copper in a form other than cupric oxide.
Nevertheless, it would be prudent for elderly people wishing to take large amounts of zinc to
consult with a doctor.
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.24 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.25
Zinc competes for absorption with copper,
iron,26 27 calcium,28 and magnesium.29 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.30 Long-term users of NAC may consider adding supplements
of zinc and copper.
Are there any drug
interactions?
Certain medicines may interact with zinc. Refer to drug interactions for a list of those medicines.
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