Bottom Line: Zinc lozenges may help reduce the length of the common cold when taken early enough.
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.
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.
Zinc may help to reduce some of the adverse effects from radiation therapy in head and neck cancers patients. It was also shown to improve survival in patients with advanced nasopharyngeal carcinoma.
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 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 Zinc may enhance sperm motility indirectly.
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.
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 trace element essential for human physiologic functions, zinc is necessary for enzymatic reactions, bone formation, and regulation of synaptic signaling. It is thought to have antioxidant and immunostimulant activities and is used as a dietary supplement to treat common cold, diabetes, rheumatoid arthritis and male infertility. Zinc supplements come in different salt forms with acetate, chloride, gluconate, and sulfate being the most common. Topical administration of zinc may reduce rhinovirus infection and replication. Short-term use of zinc lozenges may reduce the symptoms associated with the common cold (2)(3)(4)(5)(22). However, data is inconsistent and adverse events have been reported (6)(7). In children with cystic fibrosis, zinc supplementation reduced oral antibiotic use for respiratory tract infections (8), and may prolong recovery in children with severe bacterial pneumonia (23). Evidence from a few studies also suggests that zinc may be effective for the treatment of tinnitus (12) and may reduce the severity of diarrhea (13)(14)(15)(20). Oral zinc supplementation (10) as well as zinc-containing topical ointments may be effective in treating warts (11). Zinc deficiency has been linked to increased risk of developing esophageal squamous cell carcinoma (1). However, excessive zinc supplementation may increase the risk of prostate cancer (16). Studies offer conflicting results regarding the efficacy of oral zinc for taste preservation following head/neck radiation therapy (8)(9). Zinc does not prolong survival in this group of patients (24). But zinc supplementation in conjunction with chemotherapy and radiotherapy was shown to improve overall survival in patients with advanced nasopharyngeal carcinoma (25). Further research is needed.
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 men with reduced sperm motility (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) 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).
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)
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.
