Everyone knows that you lose most of your body heat through your head when you go out in the cold – up to 40 or 50 percent, according to the experts. What’s more, you’ll increase your risk of catching a cold if you’re out and about on a wet wintry day, though maybe not if you take loads of vitamin C or Echinacea.
The trouble is, everybody is wrong, according to two American doctors and medical researchers. In ‘Don’t swallow the gum’, Aaron Carroll and Rachel Vreeman devastatingly debunk many of the ‘truths’ we’ve always taken for granted by looking at where they originated and whether there’s any proper research to back them up.
Is heat lost through your head?
It seems that the study that first 'proved' the heat loss theory was done by the US military some 50 years ago: subjects were dressed in arctic-survival suits without hats or hoods, and their heat loss was measured in extremely cold temperatures. Guess which parts of their bodies lost the most heat? More recent research showed that there’s nothing special about the head, say the authors; any part of the body that’s left uncovered loses heat. And if cold, wet weather plays a part in promoting colds, it’s probably because we’re more likely to huddle indoors in groups, so viruses can be passed around easily. In one study, noble volunteers who had cold virus placed in their noses before being chilled were no more likely to become infected than those who stayed warm. Having your feet chilled does seem to make you more likely to complain of cold symptoms, but the good doctors say there’s no evidence of cause and effect – it’s just that having cold feet make you feel as if you’ve caught a cold.
Cold medicine cure
We can perhaps be forgiven for believing that taking vitamin C supplements will ward off a cold – after all, the theory was originally put forward by the double Nobel prize-winning scientist Linus Pauling, back in 1970. Since that time, many more studies on possible links have been carried out but the results are rather less encouraging. In fact, say the authors, ‘a review that combined 30 of the [top quality] studies, involving over 11,000 people, showed that taking 200mg of vitamin C a day was completely ineffective in preventing illness. "They’re less dismissive of Echinacea, but with the researchers still doing battle over whether it does or doesn’t help to prevent colds or lessen their severity, the best they can offer is that 'it is not the cure to the common cold, but it may help you to feel a little better."
The importance of clinical research
The aim of the book is wider than simply separating the truth from the dross; the authors want us to understand how to distinguish between the two for ourselves. They point out that the best evidence comes from randomised, placebo-controlled trials, since these rule out bias and are the only type that can prove that one thing caused another. They’re expensive and difficult to organise, and may not be possible for other reasons. For example, you can’t make one group of people smoke then compare them to a similar group of non-smokers to test whether smoking causes lung cancer. So tobacco companies can, and occasionally do, claim that a causative link has never been proven. What’s more, say the authors, it’s impossible to prove a negative: no one has ever been born who can fly, but it’s impossible to prove that such an individual will never appear, although everything we know suggests this is pretty unlikely.
While it’s something of a relief to discover that there’s no evidence that underarm anti-perspirants cause cancer nor that pulling out a single grey hair will cause two more to grow in its place, other myths are harder to dispense with.
The well-known 'fact' that we only ever use 10 percent of our brains holds out the hope that we could develop amazing new abilities if only we put our minds to it. Sadly, it would seem that not only did Einstein never said this, as many people believe, but modern technology such as MRI and CT scans prove conclusively that it isn’t so.
Whether you’re disappointed to learn that you can’t judge the size of a man’s naughty bits by looking at his feet (or his nose or hands) may vary according to your gender – or the size of your feet. And this lack of correlation was noted even when men were asked to report their size rather than being measured by scientists.
Some myths die hard: when the authors first published some of the evidence in this book in the British Medical Journal in 2007, they were shocked at the strong reactions their article provoked. Even some doctors, it seems, find it hard to let go of long-accepted beliefs. And most of us will find a few surprises here. If nothing else, we can stop worrying about swallowed gum: apparently it won’t become stuck to the stomach wall, but will simply reappear in the loo after a couple of days.
Don’t swallow the gum... and other medical myths debunked, by Dr Aaron Carroll and Dr Rachel Vreeman; Penguin Paperback Original, £7.99.