What Is Zinc?
Zinc is a familiar, bluish-gray metal, in widespread use in industry and in medicine. It serves as a coating for iron; it galvanizes pipes; it is an ingredient in household burn and baby ointments; and it helps speed healing of the eyes when included in eye solutions. But perhaps its most important uses are those your own body finds for it.
Tiny traces of this mineral can make the difference between life and death; between normal growth, and dwarfism or perennial sexual immaturity. There are dozens of complex biochemical operations in which zinc is of paramount importance. Yet the entire body contains only about a half teaspoon of zinc. Because so little of it is needed, it is called a trace mineral. This trace, however, is crucial. The Seventh Revised Edition o f U.S. Recommended Dietary Allowance stresses, “Zinc is required for normal health and functioning in man and animals; life is incompatible with a severe deficiency”.
Fortunately, most animals find it easy to obtain enough zinc. It is liberally distributed in the soil in most areas and therefore in most plants that grow in the soil, and it is in the meat of animals that eat those plants.
But it is not everywhere. It is this fact that led to the discovery of the importance of zinc in the human diet. While it had been known since 1934 that animals required zinc, it was only in 1961 that three scientists published a paper linking human abnormalities such as dwarfism, hypogonadism (failure of the sexual organs to mature properly), and learning disabilities in children to zinc deficiency.2 These disabilities, health authorities had noted, occurred particularly frequently, and together, in certain parts of Iran and Egypt.
It turned out that these areas had two features in common that explained their high percentage of people who failed to mature properly. Iran and Egypt, countries located in a part of the world often designated the cradle of civilization, have sustained continuous human settlement for countless generations. Year after year, century after century, human beings have tilled the soil there to bring forth wheat and other grains from which to produce bread, the staff of life. Finally after long years, the soil has become depleted. In certain areas, there is so little zinc left that people who eat only locally grown produce cannot absorb enough for proper growth. And the areas of zinc-deficient soil correlate with the areas of increased frequency of dwarfism.
Another factor exacerbating local zinc deficiencies, it was discovered, is a preference in many parts of these countries for eating unleavened as opposed to leavened bread. (The Jewish tradition of eating matzo— unleavened bread— on Passover, which celebrates the Hebrews’ exodus from Egypt, may recall this Egyptian custom.) Unleavened bread, unfortunately, contains a compound called phytate that inhibits zinc absorption. Phytates, which occur in the bran portion of whole grains, are destroyed by the leavening process. In regions where bread is not allowed to rise and the soil has been overworked without replenishment for too long, zinc deficiencies are so severe that a relatively high frequency of serious deformities results.
Iran and Egypt are not the only countries where zinc deficiencies are common. Wherever the soil is eroded or the diet is incomplete, zinc deficiencies appear. In the United States, they are not so severe as to result in noticeably increased incidence of dwarfism and hypogonadism: nonetheless, even though we eat mostly leavened bread, our preference for making it with refined instead of whole grain has combined with soil depletion due to mechanized farming and other poor agricultural practices to lead to widespread borderline zinc deficiency.
How Does Zinc Work?
At the molecular level, zinc plays a role in our bodies similar to that of the skeleton for the organism as a whole: each molecule in each cell retains its structure in part because of the rigidity of the mineral zinc.
At the level of cell and protein reproduction upon which all growth depends, zinc is fundamental. It is needed for the synthesis of the two proteins that store the cells’ blueprints for reproduction— DNA and RNA. A number of minerals are involved in the process of protein manufacture carried out by RNA: zinc, calcium, iron, magnesium, and manganese all work together so that RNA can accurately reproduce each of the thousands of proteins needed by the body.
Among these proteins are the hormones that regulate growth and sex. Zinc helps stimulate production of these essential hormones. The process seems to begin, oddly enough, in the retina of the eye—which distinguishes light with the aid of zinc. The presence of light triggers a neural signal from the retina to the hypothalamus, a gland in the brain, to stimulate the production of hormones that in turn trigger hormone production in the pituitary gland. It is the pituitary which produces growth hormone, but one more level of chemical signaling is required for the production of sex hormones: the pituitary produces gonadotrophic hormones which stimulate your ovaries or testes to produce the female and male sex hormones. You can see why zinc deficiency leads to distorted growth and sexual immaturity— the symptoms first noted in Egypt and Iran.
In women, there seems to be yet another gland involved in regulating production of the sex hormones. The pineal gland, a tiny pineconeshaped gland in the brain, is a repository of zinc. Like the hypothalamus, it too is light dependent. Light seems to prevent it from secreting a hormone that inhibits the activity of the ovaries. So during the day, when sunlight streams into the eyes, the ovaries can go ahead and produce estrogen and progesterone, the female sex hormones.
Your body runs on the energy supplied by the foods you eat— mostly in the form of carbohydrates. Carbohydrates are stored in the body with the aid of insulin. But for insulin itself to be stored, zinc must be bound to it. If your diet is too low in zinc, your body may neither store insulin nor use it well. As a result, the complications of zinc deficiency can be similar to the complications of diabetes: problems metabolizing carbohydrates, circulatory problems, and liver and kidney damage.
Enzymes are the catalysts of all chemical changes in the body, but they do not operate at all times: they are activated by the nucleotides adenosine monophosphate (AMP) and guanosine monophosphate (GMP), which make up part of the DNA and RNA molecules. Together with calcium and sodium, zinc is needed to spark these nucleotides into action. Once activated by AMP and GMP, there are at least eighty enzymes that require the presence of zinc ions as a coenzyme.
One of these eighty, for example, is the carboxypeptidase enzyme. Carboxypeptidase helps break down proteins into their component amino acids during digestion. It is produced by the pancreas, and incorporates the zinc ions needed for its operation as part of its structure.
Another enzyme dependent on zinc as a coenzyme is carbonic anhydrase, present in the red blood cells. Carbonic anhydrase regulates the production of bicarbonate from carbon dioxide and water. This promotes the rapid exchange of carbon dioxide for oxygen between the blood and the cells. This exchange is the essential life function of cell respiration, without which no cell— and no breathing organism— would survive. In addition, zinc-containing carbonic anhydrase regulates the buffering function of bicarbonate, keeping the blood’s pH at the proper level of acidity.
Where Does Zinc Work?
Zinc acts throughout the body, but some systems are especially dependent on it. Knowing about these should motivate you to get enough in your diet, so let’s take a look at where zinc works especially hard.
Protein production system. Every cell in your body must construct the proteins it needs for maintenance and reproduction, and for any special functions it performs such as hormone or enzyme secretion. Zinc sees to it that the RNA in each cell correctly transmits the pattern for construction of each protein, so that amino acids— the building blocks of protein—are strung together in the right sequence. We obtain these amino acids from the proteins we eat, and zinc plays a role here, too, as we have seen. As a coenzyme of the pancreatic enzyme carboxypeptidase, zinc is needed to separate food proteins into amino acids in the intestines.
Blood cells. Zinc has a number of functions in the blood. As a coenzyme of carbonic anhydrase, it buffers the blood and assists in transporting oxygen and carbon dioxide to and from each cell. It is so important to the functioning of the red blood cells that 80 percent of the zinc in the blood is in the red blood cells’ hemoglobin. Without it, the red blood cells rupture and cell respiration becomes impossible. Zinc also plays a role in blood clotting. And in addition, zinc enables mucopolysaccharides to be formed. Mucopolysaccharides are a component of the antigens that determine your blood type.
Circulatory system. The blood plasma is the body’s transportation system. Composed mostly of water, plasma carries blood cells, platelets, food and waste particles, any microorganisms that find their way into the body, and so on, Most of the zinc in the blood plasma is bound to the water-soluble protein albumin.
Liver. In the liver, zinc helps in breaking down fatty acids and in creating cholesterol, one of the materials used in building nerve sheaths and cell membrane walls. Zinc, therefore, protects your liver just as it does your arteries: because it helps metabolize fatty acids, zinc prevents fat deposits from accumulating. This means that zinc is important in the prevention of cirrhosis of the liver. If you drink much alcohol, beware: alcohol, which contributes to cirrhosis, also causes you to excrete zinc along with other minerals, and thereby removes one of the best defenses against cirrhosis.
Bones and joints. Zinc deficiency can prevent the bones from growing to their full length, and can also cause painful bones and joints Besides being necessary in the production of growth hormone, zinc keeps children’s bones growing properly by assuring that enough blood reaches the head of the long bones. Two bone diseases, Perthe’s disease and Osgood Schlatter’s disease, have been linked to zinc deficiency.
Eyes. We have already shown that the retina requires zinc to transmit its complex messages about incoming light to the brain. Like the retina, the lens cornea and the iris of the eye also need zinc both in their formation and in their daily functioning. In children, zinc deficiency can lead to poor vision and, often, a characteristic sideways glance.
Neuromuscular system. It would be hard to overstate the importance of zinc to the nervous system. Two diseases involving nervous system degeneration, multiple sclerosis and Wilson’s disease, seem to involve low zinc levels. In multiple sclerosis, the fatty portions of the nerve sheaths degenerate, making it more difficult for the nerves to carry messages to the muscles. Wilson’s disease, a hereditary syndrome leading to brain degeneration and muscular rigidity, is characterized by the accumulation of copper in the brain, liver, kidney, and cornea of the eye— remember zinc’s role in chelating excess copper.
Immune system. We have already seen some of the roles zinc plays in the immune system. As we know, it is needed to produce histamine, one of the most important functions of which is to dilate the capillaries so that blood—carrying infection-fighting white blood cells —can rush to the scene of an injury or infection. And zinc is carried to the liver by LEM when you are sick or injured for use in the production of other substances that help fight infection.
Metabolic system. We have already outlined the ways zinc influences basic energy metabolism. It ignites the nucleotides AMP and GMP, which catalyze all the enzymes basic to energy use. It is a coenzyme in cell respiration. It helps transform carbohydrates into glucose, and as a requirement for insulin storage, it is important in the transport of glucose and its use by the cells. It is so basic to energy metabolism that life would be impossible without it.