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Zinc

Other common name(s): zinc gluconate, zinc sulfate, zinc acetate, zinc carbonate, zinc picolinate

Scientific/medical name(s): Zn, Zn++

Description

Zinc is an essential trace mineral that plays a key role in body processes such as building DNA and RNA, producing energy, regulating the immune system, and cell metabolism. It is required for wound healing, tasting, and smelling. Zinc is found in seafood, meats, nuts, eggs, cheese, grains, and other foods.

Overview

Some studies have found that zinc supplements may help reduce cancer risk in animals, but research in humans has not been as promising. A few early studies have suggested that zinc might help fight some side effects of radiation therapy, such as loss of taste and mouth sores for people being treated for cancer of the head or neck.

Zinc supplements can help fight infections in those with zinc deficiency and may be useful in people with sickle cell disease. Zinc is very popular as a cold remedy, but studies are mixed on whether it actually helps cold symptoms. The FDA has warned consumers about using zinc products in the nose because of reports that some people lost their sense of smell. Too much zinc can lead to serious effects.

How is it promoted for use?

Some people claim zinc protects against certain types of cancer, shrinks enlarged prostate glands, decreases asthma and allergy symptoms, and fortifies the skin. Some marketers claim it helps everything from anthrax and gout to menopause and varicose veins.

Some supporters claim that zinc reduces the severity and duration of the common cold. It is also promoted as an antioxidant, a compound that blocks the action of free radicals, activated oxygen molecules that can damage cells.

What does it involve?

Zinc is in a number of foods, such as enriched breakfast cereal, lean beef and pork, oysters, poultry. Lesser amounts are in whole grains and legumes such as beans, peas, nuts, and seeds . The adult recommended dietary allowance (RDA) for zinc is 11 milligrams per day for men, 8 milligrams per day for women, 11 milligrams per day for pregnant women, and 12 milligrams per day for breast-feeding women.

Zinc capsules, tablets, lozenges, and liquid "ionic zinc" are available in drug stores, pharmacies, and on the Internet. Zinc spray or ointment is sometimes applied to wounds, burns, or injuries to speed healing. Other forms of zinc, such as nasal sprays, swabs, and gels, are intended to be put in the nose rather than taken by mouth.

What is the history behind it?

Zinc has been found in metal alloys that date back to 1400 BC. In the thirteenth century, metallic zinc was produced in India. In 1500, zinc was recognized as an element by Andreas Marggraf in Germany. In the 1700s, zinc factories were built in Europe. Medical researchers began serious investigations of zinc in the body in the early 1970s.

What is the evidence?

There have been a number of studies looking at the possible roles of zinc in the body. Some researchers have focused on zinc levels in the body in people with cancer and other diseases. A few studies found that zinc levels in serum and/or inside white blood cells were often lower in patients with head and neck cancer or childhood leukemia. Low zinc levels were also linked to larger head or neck tumors, more advanced stage of disease, and a greater number of unplanned hospitalizations. However, it is impossible to know whether the low zinc level was due to the effects of the cancer, to lower dietary intake of zinc, or to some other unknown factor. Zinc nutritional status is hard to measure accurately using blood tests because of how it is spread throughout the body.

Zinc deficiency is very rare in the United States, but it can cause poor appetite and impaired immune function. In more severe cases, zinc deficiency causes hair loss, diarrhea, impotence, and eye and skin sores. Weight loss, delayed healing of wounds, taste abnormalities, and mental slowness can also occur. Children with low zinc levels may have slowed growth and delayed puberty.

Another study found a connection between zinc intake from food and supplements and a lower risk of melanoma (the most serious type of skin cancer) and pre-cancers in the mouth. More recent studies in humans do not show a consistent link between zinc supplements and lower cancer risk.

A study published in 2004 (called SU.VI.MAX) reported on more than 13,000 French adults who had taken either a combination of low doses of vitamin E, vitamin C, beta carotene, selenium, and zinc, or a placebo (sham pill). After a median of more than 7 years of follow-up, there were no major differences in cancer rates between the people who took real supplements and those who received placebo supplements. But when researchers looked at men and women separately, the men who took antioxidants had a lower risk of cancer and death from all causes than the men who had not. This was not true for the women in the study. However, the men began the study with lower levels of antioxidants, especially beta carotene and vitamins C and E, in their bodies. This may partly explain why they benefited more. It is unclear whether or how much zinc contributed to this effect.

A subgroup of more than 5,000 men from the SU.VI.MAX study was looked at specifically to find out if the supplements changed their prostate cancer risk. After about 8 years, the men taking the supplements who had started out the study with a normal prostate-specific antigen (a protein made by the prostate gland) had a slightly lower risk of prostate cancer. The men whose PSA levels had been higher at the start (3 or greater) were at slightly higher risk if they got the supplements. Neither the higher nor lower risk was statistically significant (that is, the differences could have occurred by chance).

A later study looked at a group of US men with prostate cancer. They were compared to a group of men who didn't have the disease. The men with prostate cancer were about twice as likely to be taking supplements that included zinc than the men who didn't have prostate cancer. This supported the findings from a 2007 Italian study in which men with aggressive prostate cancer were found to be more likely to have a much higher zinc intake than those without prostate cancer.

A very small randomized clinical trial in Italy involving patients with head and neck cancer suggested that zinc sulfate tablets helped reverse the loss of taste caused by radiation therapy. But a large randomized clinical trial from the Mayo Clinic reported that loss of taste was the same in patients who received the placebo and those who got zinc supplements.

Another small study in Turkey looked at patients receiving radiation therapy for head and neck cancers to find out whether zinc helped with mouth sores. Those who took zinc had milder mouth sores, and the sores developed later in the course of radiation, than they did in the people who took a placebo.

In China, researchers gave vitamin and mineral supplements to undernourished people. They found that taking zinc supplements (which were given along with Vitamin A) had no effect on cancer risk. But, there was a slight increase in risk of strokes and overall death among those who took the zinc - vitamin A supplement that persisted for 10 years after the supplement was stopped. The increased risk was not significant, meaning that it may have happened by chance.

In an analysis of the SU.VI.MAX study that focused on heart disease risk, those who took antioxidants ended up with no difference in risk factors such as cholesterol than those on placebo. In fact, the women who had received the supplement had slightly worse risk factors for heart disease than those who did not. Since this study looked at several antioxidants all together, it is difficult to say what zinc's role might have been.

Still, the immune system does not work as well when a person does not take in enough zinc. In people with zinc deficiency, supplements may help immune function. For example, studies that were done in malnourished children from developing countries found that zinc helped prevent pneumonia and diarrhea. Zinc is now added to formulas used to re-hydrate malnourished children with diarrhea. It also helped to slow down and shorten the duration of diarrhea that was caused by infection. However, zinc supplements do not help people with normal zinc levels and may cause harm if too much is taken.

Zinc has also proven useful in helping people with sickle cell disease, possibly because the illness seems to cause zinc deficiency. Studies in people with sickle cell disease report that children often grow faster if given zinc supplements. Studies also report that adults with sickle cell disease tend to have fewer serious infections and hospitalizations if they take zinc supplements.

Zinc reduces the body's absorption of copper. This has proven useful for one rare health problem. The US Food and Drug Administration (FDA) has approved a form of zinc known as zinc acetate for people with Wilson's disease, an inborn condition in which copper builds up in the body. Unlike zinc supplements sold over the counter, the prescription drug is regulated by the FDA. This means that it must meet strict quality standards, including containing the labeled amount of zinc in each tablet.

Results of studies on zinc lozenges and its effects on cold symptoms have been mixed. Two randomized, double-blind placebo studies found that zinc gluconate in a glycine base reduced the length of cold symptoms. In a review of 8 clinical trials, researchers concluded that zinc reduced the duration and severity of the common cold. Another study found that zinc gluconate lozenges were not effective in treating cold symptoms in children and adolescents. Later studies were mixed. The type of lozenge or spray, dose, timing, and other factors may affect zinc's effectiveness. Generally, zinc seemed to work best in those who used as soon as symptoms started and then every couple of hours for a few days. Further study is needed to find out whether taking zinc by mouth can help cold symptoms.

There is some evidence that zinc, with other antioxidants, may delay age-related macular degeneration in older people and the loss of vision that goes with it. One study of the effect of zinc supplements on macular degeneration noted that men taking high doses of zinc were more likely to be admitted to the hospital with urinary problems, including enlarged prostate, kidney stones, and infections than those not taking zinc. Women taking high doses of zinc had more urinary tract infections than those who were not taking zinc supplements. Still, those who took zinc also seemed live longer than those who did not. These findings deserve careful study to see whether they hold true in other groups and settings.

At this time, it is hard to say how each nutrient or nutrient combination affects a person's risk of cancer. On the other hand, studies of large groups of people have shown that those whose diets are high in vegetables and low in animal fat, meat, and/or calories have lower risks for some of the most common types of cancer. Until more is known about this, the American Cancer Society recommends eating a variety of healthful foods -- with most of them coming from plant sources -- rather than relying on supplements.

Although it is best to get vitamins and minerals from foods, supplements may be helpful for some people, such as pregnant women, women of childbearing age, and people with restricted food intakes. People on certain diuretic medicines for blood pressure may also need more zinc. If a supplement is taken, the best choice for most people is a balanced multivitamin/mineral supplement that contains no more than 100% of the "Daily Value" of most nutrients.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must be tested before being sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.
Some such products may not contain the amount of the herb or substance that is on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand. In 2007, the FDA wrote new rules to improve the quality of manufacturing for dietary supplements and the proper listing of supplement ingredients. But these rules do not address the safety of the ingredients or their effects on health.
Most such supplements have not been fully tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

The National Institutes of Health say that an adult should not take in more than 40 milligrams of zinc per day from foods and supplements combined. Taking 150 milligrams to 450 milligrams of zinc per day is linked to low copper levels, anemia, poor immune function, low levels of "good" cholesterol, and changes in the way iron works in the body. High zinc doses over long periods may increase the risk of urinary tract problems, including infections.

Very high exposure to zinc, which occurs in some industries, may contribute to the development of prostate cancer. There is also a chance that zinc supplements may slightly raise the risk of prostate cancer, especially in higher doses over a long time.

An overdose of zinc can lead to severe nausea and vomiting, headache, and fatigue. At least one death has been reported due to kidney failure.

Zinc can reduce the body's ability to absorb some antibiotics and other drugs, which can cause them to not work well. Zinc can interfere with the body absorbing copper and iron from foods and supplements.

Manufacturers of zinc nasal spray have been sued by several hundred people who reported that they lost some or all of their ability to smell and taste because of zinc nasal spray, and most have not gotten it back. Typically, these users noted severe burning in their noses when using the spray and right away found their sense of smell and taste was lost or greatly reduced. (When the sense of smell is lost, some of the sense of taste is also lost.) Some companies have stopped making zinc nasal sprays. In 2009, the FDA warned consumers about using zinc nasal swabs and nasal gels, due to reports of loss of smell with these products as well. These warnings do not apply to any form of zinc taken by mouth, such as supplements or lozenges.

Women who are pregnant or breast-feeding should take zinc supplements only if advised to do so by their doctors. If the mother has high zinc levels, it can be passed to the baby and cause copper deficiency. However, low zinc levels in the mother can also be harmful to the infant during pregnancy, and getting enough zinc is important. Pregnant women should speak to their doctor before taking any zinc supplement.

Always tell your doctor and pharmacist about any supplements or herbs you are taking. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

To learn more

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-227-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer

References

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Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.


Last Medical Review: 03/09/2011
Last Revised: 03/09/2011