How well do popular supplements work for treating colds?

Let’s look at some of the scientific evidence of the effectiveness of these supplements. Much of this information comes from the Cochran Group, an international network of scientists who compile the work of several researchers into larger studies known as “metanalyses”. By pooling data from a number of well-conducted studies, more robust and accurate conclusions can be drawn.

Zinc is commonly sold as a natural medicine for colds in tablet, lozenge, and liquid form. It is thought to decrease the ability of cold viruses to grow on or bind to the lining of the nose. While the results of studies have gone back and forth over the years regarding zinc’s effectiveness in treating colds, a recent Cochran analysis supports the evidence for zinc supplementation in treating colds. After pooling the results of several well-conducted studies, the following conclusions were drawn:

1. If started within 24 hours of the onset of cold symptoms, zinc supplementation was found to reduce the duration of colds by about a day on average.
2. People taking zinc were around half as likely to have symptoms after a week and had less severe symptoms than people taking a placebo.
3. When continued for at least five months, taking zinc supplements reduced the number of colds that developed, school absenteeism, and prescription of antibiotics in
   children

Because the dosages and duration of treatment with zinc varied across the various studies evaluated, it was impossible for the authors to specify a particular dosage or treatment period that appeared to be most effective. Furthermore, the authors warned that there was a potential for zinc supplementation to cause side effects, such as nausea. In 2009, the U.S. Food and Drug Administration warned consumers to stop using intranasal zinc products (zinc-containing homeopathic cold remedies), because of reports of anosmia (loss of smell).

Excluding vitamins and minerals, Echinacea is one of the most commonly used natural supplements. Advocates say that it is can boost the immune system and has antiviral properties, such as preventing colds. However, two 2006 metanalyses evaluating this natural remedy drew conflicting conclusions. In the first analysis, extracts of Echinacea were found to be effective in preventing cold symptoms if someone had been clinically inoculated with the cold virus. The second, a Cochrane Systematic Review, found no evidence that Echinacea was any better than a placebo at preventing the common cold. Three clinical trials funded by the National Center for Complementary and Alternative Medicine found no benefit from Echinacea for preventing or treating colds. Echinacea products vary widely, with different preparations using different species of the plant as well a different plant parts. The final word on the effectiveness of this supplement awaits further research.

Vitamin C is an important micronutrient and antioxidant. The role of vitamin C in the prevention and treatment of the common cold has been a subject of controversy for decades. Nevertheless, it is widely used as both a preventive as well as therapeutic supplement. A 2007 analysis of results from 30 clinical trials involving 11,350 participants found that taking vitamin C regularly (200 milligrams or more daily) found that:

1. When taken after a cold starts, vitamin C supplements did not make a cold shorter or less severe.
2. When taken on a daily basis as a preventive measure, vitamin C could slightly shorten the duration of a cold. In other words, the average adult who suffers with a cold for 12 days a year would still suffer for 11 days a year if that person took a high dose of vitamin C every day during that year.
3. Vitamin C supplementation could be justified in people exposed to brief periods of severe physical exercise (e.g. running a marathon) or to cold environments. In those people, taking vitamin C appeared to cut their risk of catching a cold in half.

Since the final word regarding these and other supplementsin the treatment of the common cold is still not clear, a better approach would be to prevent the cold from developing in the first place. The best methods for doing so appear to be “behavioral” in nature, such as washing your hands regularly, getting plenty of rest, limiting exposure to people with colds, and avoiding touching your nose or eyes with potentially contaminated hands.

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