coldremedies : Zinc Lozenges As A Cold Remedy
On Blog of Stuff .com- Zinc lozenges shorten the duration of symptoms from the common cold, such as a cough and runny nose, in adults but not in children.
- The lozenges must be taken frequently, starting as soon as symptoms are noticed (within 24 hours of the onset).
- Adverse side effects of short-term use of zinc are an unpleasant taste and nausea: for longer use, side effects are unknown.
- Patients and their physicians can decide whether the benefit of a shorter cold outweighs the inconvenience of frequent doses and the unpleasant taste of the lozenges.
- No preventive treatment or ultimate cure for the common cold is available.
Since there is no definitive cure for the common cold, conventional treatments aim to alleviate its symptoms. These treatments range from the use of decongestants and antihistamines for a runny nose to expectorants and antitussives for coughing. By contrast, zinc is thought to target the cold viruses that cause the symptoms. Zinc lozenges are marketed over-the-counter without a prescription. They are sold as dietary supplements in groceries, health food stores, and pharmacies. The lozenges are marketed in two forms; zinc gluconate and zinc acetate. The element zinc is the active ingredient in both forms.
Initially introduced in the early 1980's, zinc lozenges are being used by increasing numbers of people when they have colds. With the arrival of the current winter season, the lozenges once again have attracted the public's attention. In addition, the public's interest has been heightened by a recent settlement between a maker of the lozenges and the Federal Trade Commission (FTC) regarding the claims for zinc as a treatment for the cold.
In 1974, the Food and Nutrition Board of the National Research Council of the National Academy of Sciences established zinc as an essential mineral in our diet and provided a recommended daily allowance (RDA) for zinc. The RDA implies that a certain daily amount of zinc in the diet- -12 milligrams for women and 15 milligrams for men-- is essential to maintain good nutrition. Required by over 300 enzymes for their normal biological functions, zinc also is needed for the action of insulin in the body.
Good food sources of zinc include meats, liver, seafood (especially oysters), and eggs. Zinc also is found in whole-grain products such as whole wheat or rye bread, oatmeal, and whole corn. However, its effectiveness (or bioavailability) is less in these food sources. Bioavailability refers to the absorption of an element from the intestine into the blood stream so that , you know, it is available to participate in necessary biological functions in the tissues of the body. The type of food eaten can affect the bioavailability of zinc. For example, phytate (which is found in certain cereal proteins) and dietary fiber can reduce the absorption of zinc, and thereby decrease the bioavailability of zinc. An additional source of this essential mineral is multivitamin pills, which usually contain 100% of the RDA for zinc.
Since 1984, twelve controlled studies (referred to as double-blind, placebo-controlled, randomized clinical trials) were conducted to evaluate the usefulness of zinc in treating the common cold. During a double-blind, randomized trial, which is considered by scientists as the most objective and reliable study method, neither the physician nor the patient knows whether the patient is being treated with zinc or a placebo. Which patients receive the zinc or the placebo is assigned in a random order (like the flip of a coin). The placebo in these studies is an inactive, non-zinc lozenge that is made to look like, and in some instances, taste like the zinc lozenge.
Five of the randomized clinical trials, which were done in adults, determined that zinc was effective in treating the common cold if the lozenges were started within 24 hours of the onset of cold symptoms. In one study, the lozenges reduced the severity of symptoms (assessed by using a scoring system). In the other four studies, the duration of symptoms was decreased by 3 to 4 days. In all of these trials, the lozenges contained 13.3 to 23.7 mg of elemental zinc and the patients took the lozenges once every 2 hours while awake.
In another study, the treatments with zinc or the placebo were begun before the volunteer subjects were purposely injected with a cold virus. The treatments were also continued afterwards. This is the only study to evaluate the effectiveness of zinc lozenges in preventing colds. The subjects in the zinc and placebo groups came down with about the same number of colds. The zinc lozenges therefore failed to prevent colds. However, and as experienced in the other trials, the severity of cold symptoms was significantly less in the group taking the zinc than in those taking the placebo.
In five other randomized, controlled trials in adults, there was no reported benefit of zinc in treating the common cold. A close examination of each of these trials, however, revealed one or more possible explanations for the lack of benefit. In some of these trials, the dose of zinc may have been too low. For example, in one trial, each lozenge contained only 4.5 mg of zinc. In four of these trials, compounds such as citric acid, tartaric acid, mannitol, and sorbitol, which were added to improve the flavor of the zinc lozenge, may have impaired the bioavailability of the zinc. These added compounds can form chemical bonds with zinc, thereby making the ingested zinc unavailable for its therapeutic effect.
The only study done in children and adolescents showed no value of zinc lozenges in treating the common cold. This was a large, randomized, controlled trial that was well-executed. The conclusion, therefore, is that either the 10 mg of elemental zinc used in this study may have been too low to relieve cold symptoms in children or the beneficial effects of zinc on the severity and duration of colds are limited to adults.
Zinc lozenges have two noteworthy short-term adverse effects-an unpleasant taste and nausea. Side effects of zinc lozenges taken over a longer period (for example, in trying to prevent colds) have not yet been studied. Theoretically, however, an excess of zinc in the diet could interfere with the absorption of copper, which then could become deficient in the body. Accordingly, zinc lozenges should be limited to short-term therapy, such as the treatment of cold symptoms for up to about a week.
As for using higher doses of zinc, taking 300 mg of elemental zinc daily for six weeks impairs the body's immune responses. This would theoretically increase a person's susceptibility to infections. To consume that much elemental zinc daily from zinc lozenges alone, a person would have to take more than 22 lozenges per day (each containing 13.3 mg), which is almost double the maximum recommended dose. High doses of zinc also are associated with decreased levels of high-density lipoprotein cholesterol (the "good" cholesterol) in the blood, which could be another undesirable effect.
Adverse interactions between zinc lozenges and other drugs have not been reported to date. However, citric acid, which is found in oranges, grapefruits, and lemons, can inactivate zinc salts. While vitamin C has been reported to increase the absorption of iron, a similar effect on zinc has not been seen.
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