I was recently the guest of Desiree Schell on Skeptically Speaking, where we spent an hour discussing the prevention and treatment of the common cold. Here are some of the references and sources I cited or referred to during the discussion. So read along as you listen to the podcast.
We don’t get colds from being cold – it’s a viral infection, but perhaps it might feel that way. This myth may have roots in the four humors. It’s not clear that stress has an effect – because when we’re exposed to a cold virus, even a slight exposure, can be sufficient for an infection.
Treating a Cold
Despite all the products you may see on the shelf, there are only a handful of ingredients. Some antihistamines, and anti-inflammatory drugs, may be effective for pain, sneezing, runny nose, and cough. (Though the data on cough may not be as impressive as previously suspected.)
Decongestants may also provide some benefit, though the topical sprays should not be used for more than a few days.
Dextromethorphan, which may be on the label as “DM” is a cough suppressant. There is a lack of evidence showing it works for colds though – in adults and children. Codeine is the other cough suppressant you may see in cold medications, but appears to be ineffective as well.
Zinc lozenges have been studied and the effects are inconsistent. Side effects (nausea) are common, which may have compromised blinding in the trials. Avoid zinc nasal sprays, such as Zicam, which have been associated with permanent loss of the ability to smell.
Honey for cough has been studied, and while the data have been spun as positive, it’s not impressive. Parents of the children who received honey reported greater improvement than those who received DM, but the difference was not statistically significant. You should never give honey to children under 1 year of age because of a small but real risk of botulism.
Vicks Vaporub has been around since the late 1800s. While it’s popular, there’s little research to suggest it relieves cold symptoms and congestion. Here’s a nicely detailed summary of the most recent trial (PDF). The side effect profile isn’t attractive.
Vicks is an example of a “counter irritant” and they still give them that name, even though the idea that you can cure internal problems by creating external irritations has been discarded. The idea was that you’d draw the blood and toxins out by irritating the skin. So while there may be someting to counter irritants when it comes to pain perception, there’s no evidence it has any effect when it comes to infections. However, these remedies live on in the alternative medicine universe. That’s why some still advocate mustard plasters, which can cause chemical burns on the skin and also have a lack of data to support their use.
Buckley’s Mixture contains ammonium carbonate (giving it an ammonia smell), potassium bicarbonate, menthol and camphor. The ads say “it tastes awful and it works” but would be more accurate if it said “it tastes awful and anecdotal evidence says it works” – there are no published studies that have actually evaluated it. This is despite it being on the market for decades. I don’t recommend products that haven’t been studied, so I don’t recommend Buckley’s Mixture.
What about treating children? There’s little evidence that cough and cold products are effective in children and they are not recommended. Beware the products that are on the shelf, marketed as being safe for children – they may be homeopathy, which is to say, free of both active ingredients and evidence of effectiveness.
Preventing a Cold
The basic rules apply: limit contact with sick people, wash your hands, don’t touch your eyes. The virus can survive for a few hours on surfaces like doorknobs and telephones. Clean these objects regularly, and wash your hands after touching public ones, to reduce the spread of viruses.
Echinacea has been studied extensively, and it does not work for the prevention or treatment of the cold or flu. Products like Flu Shield are not backed by good evidence.
Ginseng is an active ingredient in a popular Canadian product, Cold-fx, and a number of other similar products. To the company’s credit, they’ve done some research. Unfortunately the results seem unimpressive.
Vitamin C, a favourite of Linus Pauling, is strongly associated with preventing colds. But the data show otherwise – there is no convincing effect in the general population.There is some evidence to suggest those that are in extreme cold conditions, or are extremely physically active, may benefit, but it’s really not clear this is a real effect. And there concerns about supplements like vitamin C blocking some of the beneficial effects of exercise. On the plus side, there’s little evidence of actual harm with routine supplementation.
The data with Vitamin D are evolving. There’s an association between rickets, which is vitamin D deficiency, and respiratory tract infections, and population-level study associated vitamin D levels with recent respiratory tract infections. However, trials that have randomized patients to vitamin D supplements have not yet shown a benefit with respect to colds. But stay tuned with this vitamin.
Vitamin E has an emerging harm profile that is concerning. The risks look real and there is no evidence of benefit for primary prevention. With specific exceptions, it does not look like an attractive supplement.
Garlic is often touted for preventing colds. It could have antiviral properties, but the evidence is still unimpressive. I’d like to see better evidence before recommending supplementing.
Ginger is another herb touted for colds. There’s no evidence to suggest it has any meaningful effects at all.
Elderberry is in a number of commercial products. There’s some preliminary data showing effects on symptoms and duration of illness when treating influenza-like illnesses. Yet we’ve seen this scenario with just about every herbal remedy: Promising preliminary data, followed by less impressive data when better trials are done. It would be nice to see further studies to evaluate its effectiveness.
Eucalyptus may be used for inhalation – it has not been shown to be effective, and is probably unsafe when the undiluted oil is ingested.
Astragalus is a Chinese herb promoted to prevent colds and flu. But there’s no evidence that it’s effective for preventing or treating infections.
Oscillococcinum is a homeopathic dilution of duck liver and heart extract. It’s been reviewed extensively and not only is it absurd, even by homeopathic standards, it does not have any meaningful effects.
Probiotics: Here the evidence is limited but looks promising. A Cochrane analysis considered 10 previously published papers. It concluded that people taking probiotics had 12% fewer colds. If we get 6 colds per year, that’s 1 fewer cold every two years. For that benefit, I don’t think there’s enough evidence to suggest we take probiotic supplements regularly yet. But this is another area where we need more research to confirm the initial effects observed.
Everyone loves chicken soup but there’s no good evidence to show it’s of benefit for treatment of colds. If you like chicken soup and find it comforting, go for it.
Should you “Feed a fever, and starve a cold”? The best advice is likely to eat if you’re hungry. There’s no evidence that either is harmful for the short-term.
What about humidify the air with steam? A 2011 Cochrane review notes the need for evidence of efficacy before steam can be recommended.
Alcohol? Population research suggests that light to moderate consumption of wine, particularly red wine, is associated with fewer colds. But there’s no persuasive evidence that consuming wine will reduce the number of colds you get. And consumption of alcohol in high doses is associated with the risk of pneumonia. So there is no evidence to suggest that changing or increasing your consumption will affect the cold or its duration.
Should you avoid milk? While milk may look like mucus, milk is fat emulsified in water. The protein in milk is broken down like other proteins to amino acids. Those that drink milk have no more mucus than non-drinkers. So if you want to drink mik, go for it.
Where can the average consumer look for good evidence-based information?
- I use the paid subscriptions to Up To Date and Natural Medicines Comprehensive Database. Both are excellent summaries of the literature, and good starting points.
- Tim Farley of What’s the Harm? fame created an excellent Google search engine that only searches skeptical sites. I use it all the time.
- I also use the Netting the Evidence custom search engine to search for systematic reviews at reputable sites.
- Finally the National Library of Medicine has reputable health information at MedlinePlus.