As cold and flu season ramps up, we’re reminded how common the “common cold” truly is. The average adult experiences two to four colds per year, with symptoms that can linger seven to 10 days. Most colds get better without treatment, but many people searching for a shorter illness have turned to two “natural” therapies: echinacea and zinc.
Laboratory studies have shown that substances in the echinacea flower and roots activate immune cells and block inflammation. This has spurred excitement about echinacea’s potential to shorten the duration of the common cold.
Early studies suggested that echinacea reduced cold symptoms, but more recent research has not documented any benefit, including a study of 719 cold sufferers published in 2010. People in both the echinacea and the placebo group reported symptoms lasting for about the same period: seven days.
The element zinc has antiviral effects, including against rhinoviruses, which are the most common cause of colds. Studies of zinc supplements for colds have been equally split, with half of the studies showing a benefit, and the other half showing no effect. Also, the zinc studies have a serious flaw: Zinc’s bad taste could alert people to the fact that they were taking the zinc lozenges rather than the inactive placebo version. This could have biased the results in favor of zinc working.
A recent analysis combined the results of 17 studies that included over 2,000 people. It concluded that zinc shortened the duration of colds in adults by an average of 2.6 days. On the downside, zinc lozenges, besides leaving a bad taste in your mouth, can cause nausea.
It is difficult to interpret the medical research on vitamins and herbal supplements. The ingredients in supplements sold over the counter are not standardized, and there’s no requirement for quality control, so it’s hard to know for sure if you’re taking the same thing as people in the studies. There are now consumer agencies that will provide a “seal of approval” to indicate that the product has passed certain quality measures.
Also, the people enrolled in these studies often have a variety of illnesses with differing levels of severity, making general conclusions difficult. Finally, there’s a strong placebo effect in any study with self-reported symptoms as the outcome. In the echinacea study mentioned above, researchers compared a group that received no pills with a group that received placebo pills.
The people who took the inactive placebo tended to have shorter and less severe symptoms than the people who took no pill at all.
So, the evidence that echinacea fights colds is weak. Although zinc may shorten cold duration, it may leave you with a bad taste in your mouth and a sick feeling in your stomach. The best treatment for colds may actually be prevention. Hand washing decreases the number of colds transmitted, and flu shots prevent about 80 percent of influenza cases in a typical year.