Passage IV

NATURAL SCIENCE: This passage is adapted from the article "Zinc—The Immune System's Missing Link?" by Michael Janson, M.D., which appeared in Health and Nutrition Breakthroughs (@1997 by New Hope Communications).

To the general public, minerals are far less understood or valued than vitamins, though both are equally important to physiological functions. Among minerals themselves, calcium, magnesium and iron receive a disproportionate amount of attention, even though other minerals are equally necessary. Actually, all nutrients work in concert in our tissues to keep us healthy. One may well wonder, therefore, why some minerals are held in so much higher esteem than others. Well, calcium's popularity, for example, is due largely to advertising by the dairy industry to underscore the importance of milk, and iron is well known because its deficiencies are so easy to detect.

Mineral nutrients can be found in varying quantities in both our diets and our bodies. When they are present in our bodies in large amounts (measured in grams) , they're called major minerals and include calcium, chlorine, magnesium, phosphorus, potassium, sodium and sulfur. Those that occur in smaller quantities (measured in milligrams or micrograms) are called trace minerals and include boron, chromium, cobalt, copper, iodine, iron, manganese, selenium, silicon and zinc. Deficiencies of either major or trace minerals can be as devastating to one's health as a lack of other better-known nutrients such as vitamins A,C,E and B complex.

Though zinc gets little attention, it is critical to a healthy body. Without it, more than 300 enzymes including trypsin and alcohol dehydrogenase cannot work properly, and physiological functions such as digestion and alcohol metabolism break down. The human body generally contains 1.4 g to 2.5 g of zinc. Much of this zinc is found in muscle and bone. It is also present in skin, hair and nails, as well as in the retina of the eye.

One of zinc's most essential roles is for the white blood cells of the immune system, where it helps the body fight off a range of viral infections—from strep and influenza to the common cold. Some white blood cells produce antibodies (humoral immunity),while others are phagocytes that attack and destroy invaders, thereby providing cellular immunity.

The thymus gland, located just under the sternum, controls some of our immune functions and is affected by the amount of zinc in the body. For instance, the thymus produces thymulin, a thymic peptide that is responsible for cell-mediated immunity. As we age, the thymus gland diminishes in function and size—from nearly the same size as the heart in infants to almost undetectable in elderly people. This happens in both humans and animals. Although long considered a normal process, it appears related to zinc nutritional status. A zinc supplement given to aging mice restored the function of their thymus glands and led to the glands' regrowth. Researchers thus concluded that the usual involution of the thymus gland is not inevitable and can be reversed with zinc supplements.

Thymus-derived cells (T-cells) and natural killer cells likewise depend on zinc. Both T-cells and natural killer cells support a variety of immune-system functions such as destroying foreign cells, virally infected cells and cancer cells. An in vitro study showed that zinc increased the response of T-cells to all immune stimuli by 100 percent. The authors concluded that "treatment with zinc may have immunotherapeutic relevance, particularly in the aged and stressed organism."

Zinc has been linked to the body's ability to resist viruses, especially respiratory infections. In a group of malnourished children, supplementation with zinc significantly reduced the incidence of cough, fever and respiratory secretions compared to placebo. However, after supplementation ceased, the symptoms returned to previous levels. In addition, two Italian doctors concluded that zinc deficiencies in elderly people may lead to depression of both hormonal and cellular immunity and a significant increase of susceptibility to infections.

Zinc deficiency is often the result of a poor diet—it is one of the hallmarks of malnourishment. Supplementing with zinc is quite safe—its only significant side effect is lowered copper levels in the body tissues, since the two minerals compete for absorption. Considering zinc's safety, people should consider taking zinc supplements, especially as they age—being sure to include copper in the proper balance. Most practitioners who supplement their patients' diets with zinc also recommend taking copper at a ratio of 10 mg to 15 mg zinc for each milligram of copper.