Zinc

Description

Zinc is a mineral that is essential for a healthy immune system, production of certain hormones, wound healing, bone formation, and clear skin. It is required in very small amounts, and is thus known as a trace mineral. Despite the low requirement, zinc is found in nearly every cell of the body and is a key to the proper function of more than 300 enzymes, including superoxide dismutase. Normal growth and development cannot occur without it.

General use

The U.S. Recommended Dietary Allowance (RDA) for zinc is 5 milligrams (mg) for children under one year of age, 10 mg for children aged one to 10 years old, 15 mg for males 11 years or older, 12 mg for females 11 years or older, 15 mg for women who are pregnant, and 16-19 mg for women who are lactating.

Zinc has become a popular remedy for the common cold . Evidence shows that it is unlikely to prevent upper respiratory infections , but beginning a supplement promptly when symptoms occur can significantly shorten the duration of the illness. The only form of zinc proven effective for this purpose is the zinc gluconate or zinc acetate lozenge. Formulations of 13-23 mg or more appear to be most effective, and need to be dissolved in the mouth in order to exert antiviral properties. Swallowing or sucking on oral zinc tablets will not work. The lozenges can be used every two hours for up to a week or two at most.

People who are deficient in zinc are prone to getting more frequent and longer lasting infections of various types. Zinc acts as an immune booster, in part due to stimulation of the thymus gland. This gland tends to shrink with age, and consequently produces less of the hormones that boost the production of infection-fighting white blood cells. Supplemental zinc, at one to two times RDA amounts, can reverse this tendency and improve immune function.

In another immune stimulant capacity, zinc can offer some relief from chronic infections with Candida albicans, or yeast. Most women will experience a vaginal yeast infection at some time, and are particularly prone to them during the childbearing years. Some individuals appear to be more susceptible than others. One study showed yeast-fighting benefits for zinc even for those who were not deficient in the mineral to begin with. Other supplements that will complement zinc in combating yeast problems are vitamin A, vitamin C , and vitamin E . Another measure that can help to limit problems with Candida is eating yogurt, which is an excellent source of Lactobacillus, a friendly bacteria that competes with yeast. Limiting sweets in the diet and eating garlic or odor-free garlic supplements may also prove helpful.

People who are going to have surgery are well advised to make sure they are getting the RDA of zinc, vitamin A, and vitamin C in order to optimize wound healing. A deficiency of any of these nutrients can significantly lengthen the time it takes to heal. Adequate levels of these vitamins and minerals for at least a few weeks before and after surgery can speed healing. The same nutrients are important to minimize the healing time of bedsores, burns , and other skin lesions.

There are two male health problems that can potentially benefit from zinc supplementation. Testosterone is one of the hormones that requires zinc for production. Men with infertility as a result of low testosterone levels may experience improvement from taking a zinc supplement. Another common condition that zinc can be helpful for is benign prostatic hypertrophy, a common cause of abnormally frequent urination in older men. Taking an extra 50 mg a day for three to six months offers symptomatic relief for some men.

Teenagers are often low in zinc, and also tend to experience more acne than the general population. The doses used in studies have been in the high range, requiring medical supervision, but increasing dietary zinc or taking a modest supplement in order to get the RDA amount is low risk and may prove helpful for those suffering from acne. People should consult a knowledgeable health care provider before taking large doses of any supplement.

There is some evidence that zinc supplementation may slightly relieve the symptoms of rheumatoid arthritis , but the studies are not yet conclusive. It's possible that those who initially had low zinc levels benefited the most.

In 2002, new research showed certain concentrations of zinc improved the effect of a therapy called interferon for some patients with chronic hepatitis C. Although the trial was preliminary, it showed promise for further research into zinc's effects in enhancing interferon therapy.

Zinc is sometimes promoted as an aid for memory. This may be true to the extent that vitamin B₆ and neurotransmitters are not properly utilized without it. However, in the case of people with Alzheimer's disease , zinc can cause more harm than good. Some experiments indicate that zinc actually decreases intellectual function of people with this disease. Under these circumstances, it is probably best to stick to the RDA of 15 mg as a maximum daily amount of zinc.

The frequency of sickle-cell crisis in patients with sickle-cell anemia may be decreased by zinc supplementation. The decrease was significant in one study, although the severity of the attacks that occurred was not affected. Use of zinc supplementation or other treatment for sicklecell anemia, a serious condition, should not be undertaken without the supervision of a health care provider.

Both the retina of the eye, and the cochlea in the inner ear contain large amounts of zinc, which they appear to need in order to function properly. Dr. George E. Shambaugh, Jr., M.D., is a professor emeritus of otolaryngology and head and neck surgery at Northwestern University Medical School in Chicago. In Prevention's Healing with Vitamins, he "estimates that about 25% of the people he sees with severe tinnitus are zinc-deficient." He adds that they sometimes have other symptoms of zinc deficiency. Large doses may be used in order to provide relief for this problem. Medical supervision and monitoring are necessary to undertake this course of treatment.

Topical zinc can be useful for some conditions, including cold sores. It is also available in a combination formula with the antibiotic erythromycin for the treatment of acne. Zinc oxide is a commonly used ingredient in the strongest sun block preparations and some creams for the treatment of diaper rash and superficial skin injuries. Men can use topical zinc oxide to speed the healing of genital herpes lesions, but it is too drying for women to use in the vaginal area.

There is still not enough information on some of the claims that are made for zinc. A few that may have merit are the prevention or slowing of macular degeneration , and relieving psoriasis . One should consult a health care provider for these uses.

Deficiency

It is not uncommon to have mild to moderately low levels of zinc, although serious deficiency is rare. Symptoms can include an increased susceptibility to infection, rashes, hair loss , poor growth in children, delayed healing of wounds , rashes, acne, male infertility, poor appetite, decreased sense of taste and smell, and possible swelling of the mouth, tongue, and eyelids.

A more serious, chronic deficiency can cause severe growth problems, including dwarfism and poor bone maturation. The spleen and liver may become enlarged. Testicular size and function both tend to decrease. Cataracts may form in the eyes, the optic nerve can become swollen, and color vision is sometimes affected by a profound lack of zinc. Hearing is sometimes affected as well.

Since meats are the best sources of zinc, strict vegetarians and vegans are among the groups more likely to be deficient. The absorption of zinc is inhibited by high fiber foods, so people who have diets that are very high in whole grain and fiber need to take supplements separately from the fiber. Zinc is needed in larger amounts for women who are pregnant or breastfeeding. Deficiency during pregnancy may lower fetal birthweight, as well as increase maternal risk of toxemia. A good prenatal vitamin is likely to contain an adequate amount. People over age 50 don't absorb zinc as well, nor do they generally have adequate intake, and may require a supplement. Alcoholics generally have poor nutritional status to begin with, and alcohol also depletes stored zinc.

There is an increased need for most vitamins and minerals for people who are chronically under high stress . Those who have had surgery, severe burns, wasting illnesses, or poor nutrition may require larger amounts of zinc than average.

Some diseases increase the risk of zinc deficiency. Sickle-cell anemia, diabetes, and kidney disease can all affect zinc metabolism. People with Crohn's disease , sprue, chronic diarrhea , or babies with acrodermatitis enteropathica also have an increased need for zinc. Consult a health care provider for appropriate supplementation instructions.

Preparations

Natural sources

Oysters are tremendously high in zinc. Some sources, such as whole grains, beans, and nuts, have good zinc content but the fiber in these foods prevents it from being absorbed well. Foods with better utilized zinc include beef, chicken, turkey, milk, cheese, and yogurt. Pure maple syrup also is a good source of zinc.

Supplemental sources

Zinc supplements are available as oral tablets in various forms, as well as lozenges. Zinc gluconate is the type most commonly used in lozenge form to kill upper respiratory viruses. One should select brands that do not use citric acid or tartaric acid for flavoring, as these appear to impair the effectiveness. The best-absorbed oral types of zinc may include zinc citrate, zinc acetate, or zinc picolinate. Zinc sulfate is the most likely to cause stomach irritation. Topical formulations are used for acne and skin injuries. Oral zinc should not be taken with foods that will reduce its absorption, such as coffee, bran, protein, phytates, calcium , or phosphorus . Supplements should be stored in a cool, dry location, away from direct light, and out of the reach of children.

Precautions

Toxicity can occur with excessively large doses of zinc supplements, and produce symptoms, including fever, cough , abdominal pain, nausea, vomiting , diarrhea, drowsiness, restlessness, and gait abnormalities. If doses greater than 100 mg per day are taken chronically, it can result in anemia, immune insufficiency, heart problems, and copper deficiency. High doses of zinc can also cause a decrease in high density lipoprotein (HDL), or good, cholesterol .

People who have hemochromatosis, are allergic to zinc, or are infected with HIV should not take supplemental zinc. Ulcers in the stomach or duodenum may be aggravated by supplements as well. Those with glaucoma should use caution if using eye drops containing zinc. Overuse of supplemental zinc during pregnancy can increase the risk of premature birth and stillbirth, particularly if the supplement is taken in the third trimester. This increase in adverse outcomes has been documented with zinc dosages of 100 mg taken three times daily.

Side effects

Zinc may cause irritation of the stomach, and is best taken with food in order to avoid nausea. The lozenge form used to treat colds has a strong taste, and can alter the sense of taste and smell for up to a few days.

KEY TERMS

Sickle-cell anemia

—A genetic malformation of red blood cells that can cause periodic crises in sufferers.

Interactions

The absorption of vitamin A is improved by zinc supplements, but they may interfere with the absorption of other minerals taken at the same time, including calcium, magnesium, iron , and copper. Supplements of calcium, magnesium, and copper should be taken at different times than the zinc. Iron should only be taken if a known deficiency exists. Thiazide and loop diuretic medications, sometimes used for people with high blood pressure, congestive heart failure, or liver disease, increase the loss of zinc. Levels are also lowered by oral contraceptives. Zinc can decrease the absorption of tetracycline and quinolone class antibiotics, antacids, soy, or manganese , and should not be taken at the same time of day. Drinking coffee at the same time as taking zinc can reduce the absorption by as much as half. Even moderate amounts of alcohol impair zinc metabolism and increase its excretion. Chelation with EDTA can deplete zinc, so patients undergoing chelation need to supplement with zinc, according to the instructions of the health care provider.

Resources

BOOKS

Bratman, Steven and David Kroll. Natural Health Bible. California: Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. Pennsylvania: Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & supplements: the complete guide. Arizona: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. California: Therapeutic Research Faculty, 1999.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: alpha books, 1997.

PERIODICALS

Vernarec, Emil. "Zinc May Enhance the Efficacy of Interferon." RN (May 2002): 28.

Judith Turner

Teresa G. Odle

zinc metallic chemical element; symbol Zn; at. no. 30; at. wt. 65.38; m.p. 419.58°C; b.p. 907°C; sp. gr. 7.133 at 25°C; valence +2. Zinc is a lustrous bluish-white metal. It is found in Group 12 of the periodic table . It is brittle and crystalline at ordinary temperatures, but when heated to between 110°C and 150°C it becomes ductile and malleable; it can then be rolled into sheets. It is a fairly reactive metal. Although it is not abundant in nature, it is of great commercial importance. It is used principally for galvanizing iron, but is also important in the preparation of certain alloys, e.g., Babbitt metal , brass , German silver , and sometimes bronze . It is used for the negative plates in certain electric batteries and for roofing and gutters in building construction. Since the metal reacts with dilute mineral acid to liberate hydrogen, it is often used for this purpose in the laboratory. Zinc compounds are numerous and are widely used. Perhaps most important is zinc oxide , or zinc white, a versatile compound with many uses. Other zinc compounds include zinc chloride, used as a wood preservative, in soldering fluxes, as a mordant in dyeing textiles, and in adhesives and cements; and zinc sulfide, used in making lithopone as well as television screens and X-ray apparatus. The chromate, zinc yellow, serves as a pigment; sodium zincate, as a water softener and as a flocculating agent in water purification. The crystalline sulfate is known commonly as white vitriol. Zinc is essential to the growth of many kinds of organisms, both plant and animal. It is a constituent of insulin, which is used in the treatment of diabetes. Chief sources of zinc are the sulfide ore, zinc blende, or sphalerite (called also blende or "black Jack" ); zincite, an oxide; calamine, a silicate; and smithsonite, the zinc carbonate. Zinc ores are widely and abundantly distributed throughout the world. The United States is the leading producer. The metallurgy of zinc depends upon the ore used. The sulfide ore is roasted to the oxide, then mixed with coal and heated to 1,200°C. The zinc vaporizes and is condensed outside the reaction chamber and cast into blocks called spelter. In another method the ore is processed by flotation, filtering, roasting, and leaching; the resulting solution is filtered and the zinc removed by electrolysis.

Zinc

melting point: 419°C
boiling point: 907°C
density: 7.14 g/cm ³
most common ions: Zn ²⁺

Like many transition metals , zinc has been known in impure form since ancient times. Brass (copper and zinc) coins were used by Egyptians and Palestinians as early as 1400 b.c.e. The first purification of zinc probably occurred during India in the thirteenth centuryc.e. Although the origin of the name is unknown, it has been suggested that it derives from the German word Zincke, meaning "spike" or "tooth."

Zinc is a trace element (with an abundance of 0.0076%) in Earth's crust. Like the other elements in its family, zinc is found predominantly as a sulfide compound (ZnS). Pure zinc is a silver-white solid at room temperature. Like other metals , zinc conducts electricity and can be formed into wires or sheets. Some properties of zinc are quite different from those of the other transition metals—namely, its relatively low melting point, boiling point, and density. These different properties are attributed to zinc's full outermost subshell of electrons, which also causes it to be relatively unreactive.

Due to the low reactivity of zinc, its most common use is in anticorrosion coatings. Zinc is also often used to form alloys , including brass and commercial bronze. Pennies minted after 1983 are made of a core of zinc surrounded by copper. Historically, zinc was used by Alessandro Volta in 1800 to produce the first battery. Zinc ions, due to their low reactivity, are important biologically. In animals zinc is the most abundant metallic cofactor ; it is used by insulin in the regulation of glucose consumption and by hydrolytic enzymes. An adult human body contains 2 to 3 grams (0.071–0.106 ounces) of zinc.

see also Cofactors; Volta, Alessandro.

Thomas B. Rauchfuss

Amanda Lawrence

Bibliography

Greenwood, N. N., and Earnshaw, A. (1997). Chemistry of the Elements, 2nd edition. Boston: Butterworth-Heinemann.

Nechaev, I., and Jenkins, G. W. (1994). Chemical Elements: The Exciting Story of Their Discovery and of the Great Scientists Who Found Them. Jersey City, NJ: Parkwest.

Internet Resources

WebElements—Periodic Table. Available from <http://www.webelements.com/>.

zinc An essential mineral which forms the prosthetic group of a large number of enzymes, and also the receptor proteins for steroid and thyroid hormones and vitamin A and vitamin D. Deficiency results in hypogonadism and delayed puberty, small stature, and mild anaemia; it occurs mainly in subtropical regions where a great deal of zinc is lost in sweat, and the diet is largely based on unleavened wholemeal bread, in which much of the zinc is unavailable because of the high content of phytate.

Meat, fish (especially shellfish), legumes, and (leavened) wholegrain cereals are rich sources. Synergistic zinc is a trade name for zinc supplement that also contains copper and vitamin A, which are claimed to aid its absorption.

429. Zinc

See also 270. METALS .

photozincography

Obsolete, a type of photoengraving using a sensitized zinc plate.

sherardisology

the coating of steel and iron with a thin cladding of zinc. —sherardize , v.

zincography

1. a lithographic or offset process using zinc plates.

2. a letter press printing process using engraved or photoengraved zinc plates. —zincographer , n. —zincographic, zincographical , adj.

zinc / zingk/ • n. the chemical element of atomic number 30, a silvery-white metal that is a constituent of brass and is used for coating (galvanizing) iron and steel to protect against corrosion. (Symbol: Zn) ∎  [usu. as adj.] galvanized iron or steel, esp. as the material of domestic utensils or corrugated roofs: a zinc roof. • v. [tr.] [usu. as adj.] (zinced ) coat (iron) with zinc or a zinc compound.

zinc(Zn) An element that is required by plants. It is found bound to a variety of enzymes, stabilizing them and also being involved in catalysis. Deficiency in plants prevents the expansion of leaves and internodes, giving a rosette style of plant. It is a growth factor in some rodents and a constituent of certain mammalian enzymes.

zinc (zink) n. a trace element that is a cofactor of many enzymes. Deficiency is rare with a balanced diet but may occur in alcoholics and those with kidney disease; symptoms include lesions of the skin, oesophagus, and cornea and (in children) retarded growth. Symbol: Zn.

zinc (Zn) An element that is required by plants. It is found bound to a variety of enzymes, stabilizing them and also being involved in catalysis. Deficiency in plants prevents the expansion of leaves and internodes, giving a rosette style of plant.

zinc Symbol Zn. A blue-white metallic element that is a trace element (see essential element) required by living organisms. It functions as the prosthetic group of a number of enzymes.

zinc hard bluish-white metal. XVII. — G., of unkn. orig. Comb. form zinco- as in zincography.

Zn • symb. the chemical element zinc.

Zn symbol for the element zinc .

Zn See zinc.

Zn See ZINC.

zinc •ankh, bank, blank, clank, crank, dank, drank, embank, flank, franc, frank, hank, lank, outflank, outrank, Planck, plank, point-blank, prank, rank, sank, shank, shrank, spank, stank, swank, tank, thank, wank, yank •sandbank • piggy bank • mountebank •fog bank • mudbank • Bundesbank •databank • riverbank • Burbank •greenshank • sheepshank •scrimshank • Cruikshank •think tank • Franck • Eysenck •bethink, blink, brink, chink, cinque, clink, dink, drink, fink, Frink, gink, ink, interlink, jink, kink, link, mink, pink, plink, prink, rink, shrink, sink, skink, slink, stink, sync, think, wink, zinc •rinky-dink • Humperdinck • iceblink •cufflink • bobolink • Maeterlinck •lip-sync • countersink • doublethink •kiddiewink •tiddlywink (US tiddledywink) •hoodwink

ZN airline flight code for Eagle Airlines
• Irish vehicle registration for Meath
• international civil aircraft marking for New Zealand

Zn Chem., symbol for zinc