In the public eye, minerals often take a back seat to vitamins, although they are equally important to physiological functions. Even among the minerals, calcium, magnesium and iron receive more attention than other critical elements. All nutrients work in concert in our tissues to keep us healthy, however, and a mineral's popularity is generally due to factors other than its singular importance; calcium's popularity, for example, is due mainly to the dairy industry's advertising campaign, and iron is well known because its deficiencies are so easy to detect.

Mineral nutrients are present in various quantities in both the diet and the body. Those present in the body in large amounts (measured in grams) are called the 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 our health as a lack of other better-known nutrients such as vitamins A, C, E and B complex.

Zinc: An Unsung Mineral
Zinc is an often overlooked mineral that plays an important role in 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. ¹ 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 and in the prostate gland.

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 infectionsfrom strep and influenza to herpes and the common cold. Some white blood cells produce antibodies (humoral immunity), while others are phagocytes that attack and destroy invaders and thereby provide 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, and 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. ² 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. ³ 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. ⁴ In a group of malnourished children in Ecuador, 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 humoral and cellular immunity, a significant increase of susceptibility to infections, and an increase in morbidity and mortality. ⁵

Zinc deficiency is often the result of a poor diet - it is one of the hallmarks of malnourishment - but it can also be caused by poor intestinal absorption or excessive zinc loss resulting from trauma, burns, stress, bleeding, diabetes or chelation therapy (proper protocol for chelation includes zinc supplements). It is difficult to evaluate the body's level of zinc because no single laboratory test is ideal. Physicians must therefore rely on the signs and symptoms of zinc deficiency as well as on lab tests.

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.

Zinc And The Common Cold
Despite research showing that zinc improves immunity, clinicians still don't know for certain if zinc supplements can help treat a common cold in people who are not grossly malnourished. (Studies on malnourished people may not accurately reflect how supplements affect a healthy person.) A number of studies, however, suggest that supplementation can help.

A 1989 in vitro study showed that zinc chloride can inhibit growth of rhinoviruses, which along with coronaviruses and adenoviruses are responsible for most colds. 6 A 1984 clinical trial demonstrated that the duration of colds was cut in half in the subjects taking zinc (23 mg every two hours) compared to those taking a placebo. ⁷ After seven days, 86 percent of the zinc group were free of symptoms, compared to only 46 percent of the placebo group. In a 1987 clinical study, it was shown that zinc gluconate lozenges reduced the symptom score from 8.2 to 5.7 (a 30 percent reduction) in subjects who developed upper respiratory infections after being exposed to an infecting dose of rhinovirus. ⁸

However, several investigators in early controlled studies did not find zinc helpful for treating colds. ^9,10 They suggested that the controls in previous studies (other than the ones mentioned above) were inadequate because the intensely bitter taste of zinc would have made blinding difficult. The researchers also described side effects in the zinc-treated groups, but these were mainly due to the taste of the zinc leading to nausea and temporarily altered taste buds. ¹¹

Yet even in this purportedly negative study, the authors admitted that the zinc-treated group had reduced symptom severity - a statistically significant 7 percent to 9 percent. The dose of zinc and the specific zinc compounds used varied from study to study, and this may account for discrepancies.

Most recently, researchers demonstrated a significant reduction in cold symptoms in a group of 50 patients given zinc gluconate lozenges compared to a placebo group of 50 controls. ¹² The colds were significantly shorter in the zinc group than in the placebo group (4.4 days versus 7.6 days). The zinc group also had significantly fewer days of coughing, headache, hoarseness, nasal congestion, nasal drainage and sore throat. Recognizing that zinc lozenges apparently do help treat viral respiratory infections, other researchers attempted to identify some of the potential mechanisms at work, concluding that the interruption of viral binding sites was most likely a factor. ¹³

Supplements That Are Easy To Swallow
One problem associated with zinc is no longer an issue - its bitter taste is easily masked in lozenge-type supplements. The supportive research cited suggests that lozenges are worth taking at the onset of a cold because of their potential to help treat viral upper respiratory infections. But zinc itself is by no means a cure-all nor an isolated magic bullet. Zinc supplements are best considered as part of a comprehensive immune-enhancing program that includes other nutrients such as vitamins A, B 6 , C and E. Essential fatty acids and Co-Q10 are also important to a healthy immune system and should be taken routinely. Immune-stimulating herbs such as Echinacea angustifolia or E. purpurea and Oregon graperoot (Mahonia aquifolium) also help build immunity and reduce respiratory infection symptoms. Add a whole-foods diet low in sugar (sugar inhibits white cell function), regular exercise and a stress management program and you'll have a true prescription for a strong immune system.

Michael Janson, M.D., is president of the American Preventive Medical Association and a fellow and president-elect of the American College for Advancement in Medicine. Janson is the author of The Vitamin Revolution in Health Care. He practices nutrition therapy, chelation therapy and preventive medicine at the Center for Preventive Medicine in Barnstable, Mass.

REFERENCES

1. Linder, M. ed. Nutritional Biochemistry and Metabolism, New York, Elsevier Science Publishing, 1991.

2. Mocchegiani, E., et al. "Reversibility of the thymic involution and of age-related peripheral immune dysfunctions by zinc supplementation in old mice," Int J Immunopharmacol, 17(9): 703-18, September 1995.

3. Saha, A.R., et al. "Zinc induces thymulin secretion from human thymic epithelial cells in vitro and augments splenocyte and thymocyte responses in vivo," Int J Immunopharmacol, 17(9): 729-33, September 1995.

4. Sempertegui, F., et al. "Effects of short-term zinc supplementation on cellular immunity, respiratory symptoms, and growth of malnourished Equadorian children," Eur J Clin Nutr, 50(1): 42-46, January 1996.

5. Ripa, S. & Ripa, R., "Zinc and the elderly," Minerva Med 1995, (6): 275-8, June 1995.

6. Merluzzi, V.J., et al. "Evaluation of zinc complexes on the replication of rhinovirus 2 in vitro," Res Commun Chem Pathol Pharmacol, 66(3): 425-40, December 1989.

7. Eby, G.A., et al. "Reduction in duration of common colds by zinc gluconate lozenges in a double-blind study," Antimicrob Agents Chemother, 25(1): 20-24, January 1984.

8. Al-Nakib, W., et al. "Prophylaxis and treatment of rhinovirus colds with zinc gluconate lozenges," J Antimicrob Chemother, 20(6): 893-901, December 1987.

9. Douglas, R.M., "Failure of effervescent zinc acetate lozenges to alter the course of upper respiratory tract infections in Australian adults," Antimicrob Agents Chemother, 31(8): 1263-65, August 1987.

10. Farr, B.M., et al. "Two randomized controlled trials of zinc gluconate lozenge therapy of experimentally induced rhinovirus colds," Antimicrob Agents Chemother, 31(8): 1183-87, August 1987.

11. Smith, D.S., et al. "Failure of zinc gluconate in treatment of acute upper respiratory tract infections," Antimicrob Agents Chemother, 33(5): 646-48, May 1989.

12. Mossad, S.B., et al. "Zinc gluconate lozenges for treating the common cold. A randomized, double-blind, placebo-controlled study," Ann Intern Med 15;125(2): 81-88, July 1996.

13. Novick, S.G., et al. "How does zinc modify the common cold? Clinical observations and implications regarding mechanisms of action," Med Hypotheses 46(3): 295-302, March 1996.