The common cold is a viral infection of the upper respiratory system. On average, children have six to eight colds per year, and adults have two to four. The common cold places a heavy burden on society, accounting for approximately 40% of time taken off work and millions of days of school missed by children each year. While medical science has yet to develop a cure for the common cold, many people take a variety of supplements in the hopes that they will prevent or shorten the duration of the illness. The most popular of these supplements are zinc, vitamin C, and Echinacea.
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 "meta-analyses". 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 on average, by about a day.
2. People taking zinc were less likely to have their symptoms persist beyond seven days of treatment and had less severe symptoms than people taking a placebo.
- 3. Although various dosages were of zinc were used in the studies evaluated, a dose of 75 mg/day (or higher) was thought to be best to use for treating colds.
Except for 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 meta-analyses 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 also 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.
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 meta-analysis of results from 30 clinical trials involving 11,350 participants 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.