December 13, 2012.
UC Berkeley Wellness Letter examines how effective these supplements are.
A cure or preventive for the common cold has been a holy grail for medical researchers and drug companies. So far nothing has worked — medications for colds simply relieve some symptoms temporarily, at best. No wonder, then, that people are tempted by the cold-fighting and/or immunity-boosting claims made for many dietary supplements. Do any of them stand up to scientific scrutiny?
Some supplements with purported cold-fighting ability are single nutrients or herbs. Others try to impress with a mind-numbing list of ingredients.
The best known supplement that throws the kitchen sink at colds, Airborne contains vitamins (A, C, E), minerals (magnesium, zinc and selenium) and echinacea, ginger and a bouquet of other herbs. In 2008, the Federal Trade Commission accused the company of making unproven claims about curing and preventing colds and flu; the company had to pay a $30 million settlement. So now the ads and packages merely say that Airborne “supports” the immune system (wink, wink).
Some of the ingredients in Airborne and other formulas have been tested in controlled studies, with inconsistent results. But there have been no clinical trials testing the specific formulas, at least none that have been published in peer-reviewed journals.
Our take: Forget about Airborne and similar formulas. They’re a waste of money. And if taken often, Airborne may weaken bones because of its relatively high level of vitamin A.
Lab research suggests that this herbal remedy, usually Echinacea purpurea, can stimulate the immune system and have direct antiviral and anti-inflammatory effects. But human studies on echinacea’s effect on colds or immunity have had inconsistent results. Commercial preparations vary widely in the species and the parts of the plants used, making it hard to compare results. Two large, well-designed studies in 2010 and 2011 found that echinacea was not better than a placebo at preventing colds or reducing their severity.
Our take: The claims about echinacea for colds have yet to be supported by solid research.
Despite a common belief that garlic can prevent colds, there has been remarkably little human research on this. This year a study in Clinical Nutrition found that an aged garlic extract taken for three months did not reduce the incidence of colds or flu, but did reduce their severity somewhat when they did occur.
Our take: Garlic is no more likely to keep away colds than to repel vampires, unless you eat it raw and the smell makes cold sufferers stay away from you.
Like echinacea, this herbal cure-all can affect certain aspects of the immune system, though it’s not clear what practical significance this has. Commercial preparations vary widely. A few preliminary studies suggest that Cold-fX, a patented standardized extract of North American ginseng, may help reduce the frequency and severity of colds (and flu) when taken twice daily throughout the winter, a claim allowed by Health Canada, which functions like the our FDA. There’s no evidence that it can provide relief once you have symptoms, though marketers have sometimes claimed or strongly suggested this. In the U.S., Cold-fX is available only online.
Our take: Cold-fX may help against colds and flu when taken daily for several months. But at about $30 a month, we don’t think it’s worth it. Moreover, long-term use raises questions about possible interactions with drugs (such as the blood thinner warfarin) and potential problems in people with certain health conditions (such as autoimmune disorders).
These supplements contain “friendly” bacteria that are supposed to strengthen immunity, among other proposed benefits. But studies on whether they can curb colds and other respiratory infections have been inconsistent. One problem is that supplements use countless different strains and doses. In 2011, the Cochrane Collaboration, which evaluates medical research, concluded that probiotics may help prevent acute respiratory infections, though there were limitations in the studies and no data for older people.
Our take: We don’t recommend probiotic supplements for cold prevention. We’ll discuss probiotics in an upcoming issue.
This gained popularity in the 1970s when Linus Pauling claimed it could prevent and alleviate colds. However, numerous studies have failed to confirm any benefit. According to a Cochrane Collaboration review in 2010, vitamin C supplements do not prevent colds, except perhaps in people exposed to severe physical stress, such as marathon runners and skiers. And research on the vitamin’s potential role in reducing the severity and/or duration of cold symptoms when taken at their onset has yielded mixed results.
Our take: The tide has turned against vitamin C. If there were a significant benefit, it wouldn’t be so hard to prove.
Some experts believe that vitamin D can help protect against respiratory infections, in part because it plays key roles in the immune system. Many studies have found that people with low blood levels of D are at increased risk for colds and other upper respiratory tract infections.
But the few clinical trials have had mostly disappointing results. For instance, a study from Winthrop Hospital in New York in 2009 found that 2,000 IU of vitamin D a day, taken for 12 weeks, did not reduce the risk of upper respiratory tract infections. And in a study from New Zealand in the Journal of the American Medical Association in October, monthly megadoses of D (100,000 IU), taken for 18 months, also did not reduce the risk. The great majority of subjects in both studies started with sufficient blood levels of D, however, so it’s not known if people who were deficient would have benefited.
Our take: There are some good reasons to take vitamin D supplements, notably for bone health — but not for cold prevention. More on vitamin D.
This mineral is also essential for immunity. In lab studies, large amounts of zinc can block cold viruses from adhering to the nasal lining and/or replicating themselves. Earlier this year a Cochrane Collaboration review concluded that, compared to a placebo, zinc lozenges can shorten colds by about a day and reduce their severity somewhat, particularly when started within 24 hours of the first symptoms, though not all the studies found a benefit. Another 2012 research review, in the Canadian Medical Association Journal, came to similar conclusions. There is no good research showing that zinc will prevent colds, however.
Our take: Because of possible side effects (nausea, diarrhea, cramps and a bad taste in the mouth) and questions about the effectiveness of some formulations, the Cochrane authors concluded that zinc lozenges, taken during the first day of symptoms, are “advised with caution.” We agree. Prolonged use of high doses of zinc can interfere with the absorption of copper and actually impair immune function. Don’t use any zinc product that’s applied directly in the nose; this can damage the sense of smell, possibly permanently.
There’s no convincing evidence that any supplement can prevent or treat colds. “Cold remedies,” including many over-the-counter drugs, may well make you feel better, since they have a strong placebo effect. That is, if you expect or hope that a remedy is going to help, there’s a fair chance it will, whether it contains vitamins, herbs or just plain old sugar. And, of course, remedies may seem to work because colds go away on their own. Though we don’t recommend them, it probably can’t hurt to take such products when you feel a cold coming on, but taking them throughout cold season, as is sometimes recommended, increases the risk of adverse effects.
Read more from the Berkeley Wellness Letter