Bottom Line: Zinc lozenges may help reduce the length of the common cold when taken early enough. It is unclear whether zinc lozenges can help preserve taste in people undergoing radiation for head and neck cancers. There is no proof that zinc can treat rheumatoid arthritis, diabetes, infertility, or other medical conditions.
Zinc is necessary for a number of processes in the human body. Nearly 100 specific enzymes depend on zinc as a cofactor, including those involved in the important processes of processing DNA, detoxifying alcohol, and carrying carbon dioxide in the blood, among others. Zinc is essential for many molecules to act correctly, for normal nerve signaling to occur, and for the body to have adequate immunity. In addition, is has been shown to influence programmed cell death (apoptosis) as well as the transmission of signals within the cell. However, despite the fact that all of these bodily functions require the presence of zinc, it does not necessarily follow that taking more zinc will further enhance these functions.
Scientists think that zinc lozenges or nasal sprays may prevent the virus that causes the common cold from attaching to the nasal cavities, windpipe, and lungs. In laboratory experiments, zinc interacts with the virus' "coat" and changes its ability to assemble into mature virus particles.
As an antioxidant Zinc is known to have antioxidant activity.
To prevent and treat the common cold Several clinical trials show that short-term use of zinc lozenges may reduce the duration of symptoms associated with the common cold, if started within 24 hours of onset of symptoms. However, side effects are commonly reported.
To treat diabetes No scientific evidence supports this use.
To stimulate the immune system There is no proof from clinical trials that zinc can stimulate the immune system.
To prevent and treat impaired taste from radiation therapy for head and neck cancers Two small studies offer conflicting results regarding the use of zinc for taste preservation following head and neck radiation therapy, and additional studies are needed.
To treat male infertility No scientific evidence supports this use.
To prevent and treat macular degeneration No scientific evidence supports this use.
To treat rheumatoid arthritis No scientific evidence supports this use.
To treat viral warts One small study shows that oral zinc supplementation was more effective than placebo at clearing up viral warts such as plantar, common and plane warts.
To treat tinnitus Results from a few small studies showed that zinc may be useful for the treatment of tinnitus.
To treat diarrhea Several studies have shown that zinc may be effective in the treatment of diarrhea in children.
Common cold: A randomized controlled trial evaluated the use of Cold-Eeze™ zinc lozenges for treating the common cold in school children. Within 24 hours of experiencing cold symptoms, the 249 children were given either zinc lozenges or similar-tasting placebo lozenges and were told to take them five to six times daily. Overall, children taking zinc lozenges had their colds for just as long as children taking placebo lozenges, and had the same number of days absent from school. However, more children taking zinc complained of side effects like taste disturbances, diarrhea, and nausea. These results suggest that a 10 mg zinc lozenge administered five to six times daily does not improve symptoms associated with the common cold.
A similar randomized, controlled trial looked at the ability of zinc lozenges to treat the common cold in adults. Within 24 hours of experiencing cold symptoms, 99 healthcare professionals took zinc or placebo lozenges every two hours. In this study, people taking zinc lozenges had their cold symptoms for only 4.4 days, on average, while people taking the placebo had theirs for an average of 7.6 days. Although these results support the use of zinc lozenges for treating the common cold, complaints of nausea and taste disturbances were common in the zinc group.
In a similar, but poorly-designed, clinical trial, researchers compared zinc lozenges to placebo lozenges for treating the common cold. Eighty patients participated in the study. Patients taking zinc lozenges saw their symptoms clear up more quickly than those taking the placebo, but, because of the design problems in this study, these results cannot be taken as seriously as those from other studies.
The use of a zinc nasal gel (Zicam®) for the common cold was evaluated in a randomized, controlled trial. Within 24 hours of experiencing cold symptoms, 213 patients began taking Zicam® or a placebo gel, one nasal puff every four hours. Patients using Zicam® showed a dramatic shortening of cold symptoms, averaging two to three days compared to around nine days in the placebo group. In contrast to other studies, patients taking zinc did not report a greater number of side effects.
In order to test whether a zinc intranasal gel spray can prevent the common cold, 91 volunteers used the zinc spray or a placebo spray for three days and then were inoculated with the virus that causes the common cold (i.e., it was placed in their nose). They continued using the same spray for another six days. In both the zinc and placebo groups, about three out of four volunteers developed a cold and had equally severe symptoms, indicating that the zinc spray offered no protection.
This product is regulated by the FDA as a dietary supplement. Unlike approved drugs, supplements are not required to be manufactured under specific standardized conditions. The product may not contain the labeled amount or may be contaminated. In addition, it may not have been tested for safety or effectiveness.
Consumption of more than 100mg of zinc supplement per day may increase the risk of prostate cancer.
You are taking fluoroquinolones (e.g. ciprofloxacin, levofloxacin, gatifloxacin) (If zinc is taken at the same time, it can decrease the availability and effectiveness of fluoroquinolones. Therefore, zinc should be taken either two hours before or four hours after these medications).
You are taking tetracyclines (e.g. doxycycline, minocycline) (If zinc is taken at the same time, it can decrease the availability and effectiveness of tetracyclines. Therefore, zinc should be taken either two hours before or four hours after these medications).
You take mineral or vitamin supplements (If zinc is taken at the same time, it can decrease the absorption and effectiveness of these supplements. Therefore, patients should take zinc two hours before or after foods high in calcium, phosphorus, bran fiber, or phytate).
When taken orally, zinc lozenges can cause taste disturbances, nausea, vomiting, upset stomach, or diarrhea.
When taken orally at large doses (100-300 mg/day), zinc can cause chronic toxicity including copper deficiency, depressed immune function, headache, chills, fever, and fatigue.
A naturally occurring element necessary for several human physiologic functions, zince is used by patients to shorten the duration of the common cold, as an immunostimulant, and to treat male infertility (sperm motility), diabetes, rheumatoid arthritis, and loss of taste resulting from head/neck radiation therapy. Zinc possesses antioxidant activity and is necessary for enzymatic reactions, formation of bone, and regulation of synaptic signaling. Zinc deficiency has been linked to increased risk of developing esophageal squamous cell carcinoma (1). Topical administration of zinc (e.g., lozenges or nasal spray) may affect the ability of rhinoviruses to infect humans and replicate inside a host, and numerous studies show that if initiated within 24 hours of onset, short-term use of zinc lozenges may be effective in reducing the duration of symptoms associated with the common cold with low toxicity (2)(3)(4)(5). However, data is inconsistent and adverse events are reported in approximately half of all subjects (6)(7). In children with cystic fibrosis, zinc supplementation reduced oral antibiotic use for respiratory tract infections (8). Two small studies offer conflicting results regarding efficacy of oral zinc for taste preservation following head/neck radiation therapy (8)(9). Oral zinc supplementation (10) as well as zinc-containing topical ointment (11) may be effective in treating recalcitrant viral warts. Evidence from a few studies also suggests that zinc may be effective for the treatment of tinnitus (12). Furthermore, in children, zinc may be effective in reducing the duration and severity of acute and persistent diarrhea (13)(14) as well as diarrhea associated with cholera (15). Conclusions from a meta-analysis indicate that zinc may be effective in reducing the duration and severity of acute and peristent diarrhea in children (20). Commonly reported adverse events include nausea, diarrhea, and taste disturbances (6). Consumption of more than 100mg of zinc supplement per day may increase the risk of prostate cancer (16). Chronic toxicity consisting of copper deficiency, headache, nausea, and fatigue may occur with doses as low as 100 mg/day (17)(18). Zinc may reduce the bioavailability of fluoroquinolones or tetracyclines when administered concomitantly; zinc should be given 2 hours before or 4 hours following these medications (19).
Zinc performs a number of catalytic, structural, and regulatory functions. Many specific enzymes including RNA polymerases, alcohol dehydrogenase, carbonic anhydrase, and alkaline phosphatase depend on zinc as a cofactor. Zinc is essential for the structural formation of many biologically active molecules (e.g., copper-zinc dismutase), particularly enzymes with domains capable of zinc coordination. Zinc has been shown to influence both apoptosis and protein kinase C activity. Zinc reduces oxidative stress, apoptosis, and sperm DNA fragmentation in the sperm of asthenozoospermic men (20). Zinc is necessary for immunocompetence and has a regulatory role in normal synaptic signaling. Supplemental zinc (lozenge or nasal administration) may reduce the ability of the rhinovirus to attach to the human respiratory tract. Zinc appears to complex with viral coat proteins, altering assembly of viral particles (4)(21). In patients with a common cold, zinc decreases plasma soluble interleukin-1 receptor antagonist (sIL-1fa), an inhibitor of IL-á and IL-â, as well as soluble intercellular adhesion molecule-1 (sICAM-1), a cellular receptor for rhinovirus (22). Zinc concentrates in the prostate. Consumption of high dose (more than 100 mg/day) of zinc supplement has been associated with increase in prostate cancer risk (10).
Absorption: Most exogenous zinc is absorbed transcellularly in the small intestine, where the jejunum exhibits the greatest transport rate. Absorption kinetics are saturable, and efficiency of intestinal zinc absorption increases with transit time and zinc deficiency. Substantial amounts of zinc also enter the intestines endogenously. Balanced absorption and secretion of endogenous zinc reserves maintains homeostasis. Distribution: Over 85 percent of total body zinc is incorporated into skeletal muscle and bone. Plasma zinc, bound primarily to albumin at a concentration of approximately 10-15 umol/L, represents only 0.1% of total body levels. Metabolism/Excretion: Zinc is eliminated mainly in the feces, quantities ranging from less than 1 mg/day with a zinc-poor diet to greater than 5 mg/day with a zinc-rich diet. Intestinal secretions provide the major route of endogenous zinc excretion. Biliary secretion of zinc is limited. Urinary losses are less than 10 percent of normal fecal losses, but increase concomitantly with increases in muscle protein catabolism due to starvation or trauma. Zinc loss from the body also is attributable to epithelial cell desquamation, sweat, semen, hair, and the menstrual cycle. (21)
Common (oral): Taste disturbances, nausea, vomiting, dyspepsia, diarrhea. (6)(7) Toxicity (oral): Intake of 100-300 mg/day may result in chronic toxicity including copper deficiency, depressed immune function, headache, chills, fever, and fatigue. (17)(18). Consumption of more than 100mg of zinc supplement per day may increase the risk of prostate cancer (16).
Fluoroquinolones: Concomitant administration of zinc results in reduced bioavailability of fluoroquinolones (e.g. ciprofloxacin, levofloxacin, gatifloxacin). Zinc should be administered either 2 hours before or 4 hours following fluoroquinolones. Tetracyclines: Concomitant administration of zinc results in reduced bioavailability of tetracyclines (e.g. doxycycline, minocycline). Zinc should be administered either 2 hours before or 4 hours following tetracyclines. Minerals / Vitamins: Although human studies have been equivocal, patients should take zinc 2 hours before or after foods high in calcium, phosphorus, bran fiber, or phytate to avoid nonabsorbable complexes. (19)(21)
Macknin ML, et al. Zinc gluconate lozenges for treating the common cold in children: a randomized controlled trial. JAMA 1998;279:1962-7. A prospective, randomized, double-blind study that evaluated the efficacy of 10 mg zinc gluconate (n=124) or placebo (n=125) lozenges (Cold-Eeze™) administered to school children (grades 1-12) within 24 hours after reporting 2 out of 9 symptoms associated with the common cold. Lozenges were to be taken 5 or 6 times a day. Primary outcome was resolution of symptoms as reported by the subject. Demographics were similar between treatment groups except history of asthma: 7.5% in zinc group and 14.2% in placebo group. Time to symptom resolution was 9 days for both arms, with a confidence interval for the zinc and placebo groups, 7-10 days and 8-9 days, respectively. No difference in resolution of individual symptoms or days absent from school was found. A significantly greater number of patients receiving zinc reported taste disturbances, diarrhea, and nausea . The results suggest that a 10 mg zinc lozenge administered 5-6 times daily does not improve resolution of symptoms associated with the common cold.
Hirt M, Nobel S, Barron E. Zinc nasal gel for the treatment of common cold symptoms: a double-blind, placebo-controlled trial. Ear Nose Throat J 2000;79:778-80. A prospective, randomized, double-blind, placebo-controlled evaluation of 33 mM zinc gluconate (n=108) or placebo (n=105) intranasal gel administered as 1 puff in each nostril every 4 hours on upper respiratory tract symptoms associated with the common cold. Patients were randomized to treatment within 24 hours of onset of symptoms. Primary outcome was resolution of symptoms associated with the common cold. Average time to resolution for the zinc and placebo group was 2.3 ± 0.9 and 9 ± 2.5 days. Rate of adverse events were not significantly different between groups. Baseline demographics were not provided. The author suggests that Zicam® is effective in reducing the length of the common cold when initiated within 24 hours of symptom development.
Turner RB. Ineffectiveness of intranasal zinc gluconate for prevention of experimental rhinovirus colds. Clin Infect Dis 2001;33:1865-70. A prospective, randomized, double-blind, placebo-controlled evaluation of 33 mM zinc gluconate (n=41) or placebo (n=50) intranasal gel. Patients were pretreated with nasal spray for 3 days, inoculated with rhinovirus types 23 and 39 via nasal wash and then continued on current treatment for additional 6 days. Primary outcome was incidence of viral infection. Viral shedding, severity of symptoms, and serum zinc levels were also measured. Rate of infection was approximately 75% in both treatment arms and no difference in severity of symptoms was found. The author suggests that pretreatment with zinc intranasal gel has no effect on reducing the incidence of the common cold.
Coles CL, et al. Infectious etiology modifies the treatment effect of zinc in severe pneumonia. Am J Clin Nutr. 2007;86(2):39. In order to determine if the etiology of pneumonia (bacterial versus nonbacterial pneumonia) alters the efficacy of zinc adjuvant therapy, a randomized, double-blind, placebo-controlled study of 299 children (2-23 mo) hospitalized for severe pneumonia was performed. C-reactive protein (CRP) concentrations were used to determine the etiology of pneumonia. In those with suspected bacterial pneumonia, the zinc-treated group required an additional 20 hours to recover, resulting in a longer hospital stay as compared to the placebo group. No difference in time of recovery was detected in patients with nonbacterial pneumonia. Therefore, this study suggests that zinc adjuvant therapy for patients with bacterial pneumonia may increase the time to recovery and length of hospital stay. However, because the etiology of pneumonia was determined by CRP concentration, it is possible that some subjects may have been misclassified. Lin LC, et al. Effects of zinc supplementation on clinical outcomes in patients receiving radiotherapy for head and neck cancers: a double-blinded randomized study. Int J Radiat Oncol Biol Phys. 2008;70(2):368-373. One hundred subjects with cancers of the head and neck regions and undergoing radiotherapy or chemoradiotherapy participated in this study to determine if zinc supplementation (25 mg Pro-Z, 3 times daily) could affect survival, including overall survival, disease-free survival, local-free survival, and metastasis-free survival. Three-year local-free survival was minimally affected by zinc supplementation as compared to the placebo group. However, in patients with Stages III-IV disease who simultaneously received chemoradiotherapy, zinc supplementation significantly enhanced 3-year local-free survival possibly due to decreased radiotherapy-induced mucositis and dermatitis, resulting in less interruption of the chemoradiotherapy regimen. Additional studies with more participants and longer follow-up periods are necessary.
