Zinc is a dull, gray metal. Also known as Indian tin and pewter, zinc’s industrial uses have been greatly overshadowed in the past decade by its possible medical applications. As long ago as ancient Egyptian times, individuals used zinc to improve wound healing. Only recently, however, has this benefit been partially confirmed by clinical data.1

Zinc deficiency is associated with poor nutrition and is seen in cases of alcohol abuse, large body surface area burns, type 2 diabetes, malabsorption syndromes, stress, and any other type of prolonged trauma. The U.S. recommended daily allowance for zinc ranges from 5 mg per day in infants to 19 mg per day in lactating females.2

Science

Recent controversy centers on popular zinc products that claim efficacy for preventing and/or mitigating the common cold or rhinovirus. While a discussion of the cure for the common cold usually comes up in the context of a humorous anecdote, the $40 billion spent in the United States alone is nothing to laugh at.3 In spite of this intense interest, hard data regarding the use of zinc preparations for colds remain inconsistent.4

The mechanisms of action by which zinc is thought to mitigate rhinovirus infection include inhibition of viral adhesion to the nasal mucosa and alteration of the pH due to ionization of the zinc molecule.3 Zinc ions also inhibit viral replication in the upper oropharynx and nasal passageways and in vitro.3 Data supporting the migration of oral zinc from lozenges up the back of the oropharynx are highly variable but seem to rely strictly on how well the zinc is ionized in solution.5 Zinc formulations administered intranasally sought to bypass that circuitous route and deliver the ionized zinc directly to the area of viral activity. As the FDA recently announced, however, these formulations also increase adverse effects.6

In a 10-year-old Cochrane review, only 50% of randomized controlled trials (RCTs) using zinc gluconate lozenges showed benefit, and the data today are no more conclusive.4 Many of the earlier trials were poorly designed and had questionable validity. However, even a 2003 review of 14 RCTs showed only six with benefit and eight without.7 Similar contradictory results were found in studies using intranasal zinc preparations.

Since zinc is an essential nutrient, it is used to aid in healing burns, trauma, and wounds. In addition to many enzymatic actions, zinc stabilizes cell membranes and inhibits prostaglandin metabolism, thus facilitating healing.7 Claims have been made that zinc also promotes epidermal proliferation and migration.8 A number of topical skin-care products contain zinc, especially those used in the treatment of acne vulgaris. Because of its healing and cell-stabilization action, zinc is a logical ingredient in these products. A study comparing zinc oxide cream with benzoyl peroxide, showed no appreciable difference in healing of acne lesions between the two agents. However, zinc oxide cream reduced such side effects as dryness and peeling.9

Zinc preparations have also shown efficacy in speeding healing of oral herpetic lesions. In a study comparing zinc oxide/glycine cream with placebo, researchers found a 23% reduction in time to lesion resolution. From day two of the 21-day study, subjects also reported an average of 10% fewer symptoms, such as pain and itching.10

Zinc’s role in type 2 diabetes is perhaps the most intriguing of all. Epidemiologically, patients with type 2 diabetes have significantly lower serum zinc levels than healthy individuals.11 While this is not new information, few studies discuss the effect of oral zinc supplementation on diabetic control. One study showed a 0.3% drop in overall hemoglobin A1c levels after just three months of oral zinc supplementation.11  

Safety, adverse reactions, and interactions

As evidenced by the FDA’s recent announcement regarding adverse events from popular nasal zinc preparations, safety is obviously a primary concern. All literature reviewed regarding lozenges or nasal zinc preparations noted the possibility of smell and/or taste disturbances. In some cases, these senses were completely lost.

Persons taking a fluoroquinolone or tetracycline antibiotic should avoid zinc supplements for two hours before and four hours after the medication. Zinc should also be avoided for two hours before ingesting foods and supplements that are high in calcium and phosphorus to avoid formation of nonabsorbable complexes.12

Dose and how supplied

Zinc products for cold treatment come in lozenges, nasal gels, or nasal sprays. Lozenges are dosed at one every two hours while awake, and  gels/sprays are used once every four to six hours in each nostril.1 Oral supplementation varies with individual need. In a normal adult, 12-15 mg/day as zinc gluconate or sulfate is recommended.1

Summary

Recommendation of zinc supplementation must be based on the specific condition of the patient. In light of recent announcements by the FDA, the clinical safety of certain zinc products for cold symptoms is highly questionable, and these products should not be recommended until further studies are conducted. However, because of its potential benefits, oral or topical zinc should always be considered in other conditions.

References

1. National Institutes of Health. Zinc.
2. MayoClinic.com. Zinc supplement (Oral Route, Parenteral Route).
3. Caruso TJ, Prober CG, Gwaltney JM Jr. Treatment of naturally acquired common colds with zinc: a structured review. Clin Infect Dis. 2007;45:569-574.
4. Riley D. Help your patients: Tips for effective patient counseling in the treatment of URIs (Part 5 of 6). J Fam Pract. 2009;58.
5. Eby GA. Therapeutic effectiveness of ionic zinc for common colds [letter]. Clin Infect Dis. 2008;46:483.
6. U.S. Food and Drug Administration. Warnings on three Zicam intranasal zinc products.
7. Mossad SB. Effect of zincum gluconicum nasal gel on the duration and symptom severity of the common cold in otherwise healthy adults. QJM. 2003;96:35-43.
8. BioDerm Sciences, Inc. Modern wound healing: background and significance.
9. Papageorgiou PP, Chu AC. Chloroxylenol and zinc oxide containing cream (Nels cream) vs. 5% benzoyl peroxide cream in the treatment of acne vulgaris. A double-blind, randomized, controlled trial. Clin Exp Dermatol. 2000;25:16-20.
10. Godfrey HR, Godfrey NJ, Godfrey JC, Riley D. A randomized clinical trial on the treatment of oral herpes with topical zinc oxide/glycine. Altern Ther Health Med. 2001;7:59-56.
11. Al-Maroof RA, Al-Sharbatti SS. Serum zinc levels in diabetic patients and effect of zinc supplementation on glycemic control of type 2 diabetics. Saudi Med J. 2006;27:344-350.
12. Memorial Sloan-Kettering Cancer Center. Zinc.

All electronic documents accessed September 16, 2009,