Zinc, a mineral, is required in small quantities for many metabolic processes. Dietary sources include oysters, beef, and fortified cereals. Zinc supplements are available in capsule, tablet, lozenge, and nasal spray form.
(See also Overview of Dietary Supplements.)
Claims for Zinc
People most often take zinc in the form of lozenges to reduce the duration of cold symptoms. Some people take zinc to fight acne or improve heart health. Some people take zinc to slow the progression of age-related macular degeneration, which is an eye disease, or to help heal wounds because zinc deficiency delays wound healing.
Mild zinc deficiency impairs growth in children and can be corrected with zinc supplementation.
Studies suggest that zinc supplementation helps people with prediabetes or diabetes control their blood sugar levels.
Zinc supplements can prevent the body from absorbing copper; therefore, zinc is used to treat Wilson disease, a rare hereditary disorder resulting in accumulation of copper in the liver and liver damage.
Evidence for Zinc
Scientific studies are inconsistent, but if zinc has an effect on the common cold, it probably is small and occurs only when it is taken very soon after cold symptoms develop.
Strong evidence indicates that zinc supplements, when combined with certain other supplements into a standardized preparation, slow progression of moderate to severe atrophic (dry form) age-related macular degeneration. Evidence also shows that zinc may help people with diabetes and prediabetes control their blood sugar levels.
A 2016 study found that zinc supplementation may help relieve diarrhea in zinc-deficient or undernourished children (usually in low-resource countries) who are over 6 months old. There is evidence that, in low-resource countries, once-weekly supplements containing zinc and iron during the first year of life may decrease mortality due to diarrhea and respiratory infections.
Side Effects of Zinc
Zinc is generally safe, but zinc toxicity can develop if high doses are taken. The common side effects of zinc lozenges include the following:
Nausea
Vomiting
Diarrhea
Mouth irritation
Mouth sores
Metallic taste
Symptoms such as fever, coughing, headache, and fatigue
Because zinc is a trace metal and can remove other necessary metals from the body, intake of zinc lozenges should be limited (for example, to no more than 14 days). Zinc sprays may irritate the nose and throat and cause a loss of the sense of smell; they should be avoided.
Doses greater than 40 mg daily may cause toxicity, sometimes resulting in in the body and decreases in iron levels, often resulting in anemia. At daily doses greater than 50 mg, levels of the high-density lipoprotein (the "good cholesterol") may decrease. Also, prostate disorders, such as benign prostatic hyperplasia, may worsen with consumption at high doses for several years. Whether several years of high-dose use can cause or contribute to prostate cancer in unknown.
Drug Interactions with Zinc
The absorption and effectiveness of certain antibiotics in treating infection may be lowered if zinc supplements are taken at the same time; therefore, zinc should be taken at least 2 hours before or 4 to 6 hours after these antibiotics.
Wilson disease and some autoimmune disorders).
Recommendations for Zinc
Zinc supplements are not recommended for people in high-resource countries because most people in such countries get enough zinc through their diet without taking zinc supplements and taking too much zinc can lead to toxic levels with serious side effects. However, zinc supplements can decrease deaths due to common infections among children in low-resource countries.
High-dose zinc supplements should not be taken unless recommended by a doctor to treat a zinc deficiency or Wilson disease.
It is not clear whether zinc supplements reduce the duration of common colds, but any such effect is unlikely to be anything more than minimal.
Zinc may also help control blood sugar levels in people with diabetes or prediabetes.
