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Got a cold? Eat caterpillars

Why medinical zinc is not all it's cracked up to be.

Caterpillars. Photo: Getty
Delicious. Photo: Getty

How’s this for impact? At the end of January, a research group in Manchester published a paper on the essential role of zinc in the human immune system. A week later, the price of zinc rose on the international metals markets after its longest slump in 25 years.

Amazing? Of course not. These are two entirely unrelated events. But it’s the ability to separate coincidence from causality that allows us to distinguish old wives’ tales from useful information.

Zinc has been in medical use since at least the 2nd century BC. A set of pills found in the remains of a ship wrecked off the Tuscan coast in 140BC are 75 per cent zinc. They were almost certainly used to treat eye and skin disorders, a practice documented by the Roman polymath Pliny in the 1st century AD.

Zinc is still used for this purpose. It has antiseptic and antiviral properties, which is why it is often embedded in dressings for wounds. What’s more, anecdotal evidence has long suggested that taking zinc supplements helps fight the common cold. But anecdotal evidence isn’t the most trustworthy: sometimes it sees cause and effect where there is none.

Even individual studies haven’t been enough to give us the answer; depending on how they are carried out, they can produce conflicting results. Fortunately, we’ve developed even more sophisticated techniques: dissection, analysis and pooling of the scientific studies themselves. This has allowed us to draw a firm and reliable conclusion. In the case of zinc, it’s this: take at least 75mg a day and “there is a significant reduction in the duration of cold”, according to a gold-standard Cochrane Review, which looks at primary research in health care. Ancient wisdom, in this case, has some validity.

What the ancients didn’t know is the mechanism involved. Zinc deficiency, it turns out, causes more than 3,000 types of protein in the body to function inefficiently or not at all. The body responds to this as stress, causing the immune system to leap into action. Specifically, according to researchers at Manchester University, zinc deficiency unleashes a molecule called interleukin-1-beta. This is part of the armoury of the immune system. The trouble is that, in the absence of any infection to clear, firing the immune response’s weaponry just causes damage.

The zinc deficiency, as the researchers point out, could easily be resolved using dietary supplements. And this increased medical use of zinc could have an economic impact.

Not, it has to be said, in the metals markets, where the rising price of zinc is linked to China’s construction boom. But zinc use for medical purposes could be worth about $25bn a year in the US alone. That is the estimated annual impact of common colds, in terms of lost productivity. The Cochrane Review has found that taking zinc supplements for at least five months can reduce that. It certainly reduces school absences and the prescription of antibiotics for children with the common cold.

Because colds are caused by a virus, antibiotics do nothing for sufferers, yet doctors prescribe them as a placebo to get worried parents out of their surgery. So zinc supplementation also slows the spread of antibiotic resistance. Here’s a final tip in case the price of zinc lozenges skyrockets: a daily 100g of cooked caterpillars contains all the zinc you need.

You’re welcome.