When it comes to wrapping up on a cold winter's day, a cosy hat is obligatory. After all, most of our body heat is lost through our heads – or so we are led to believe.
Closer inspection of heat loss in the hatless, however, reveals the claim to be nonsense, say scientists who have dispelled this and five other modern myths.
They traced the origins of the hat-wearing advice back to a US army survival manual from 1970 which strongly recommended covering the head when it is cold, since "40 to 45 percent of body heat" is lost from the head.
Rachel Vreeman and Aaron Carroll, at the centre for health policy at Indiana University in Indianapolis, rubbish the claim in the British Medical Journal this week. If this were true, they say, humans would be just as cold if they went without a hat as if they went without trousers. "Patently, this is just not the case," they write.
The myth is thought to have arisen through a flawed interpretation of a vaguely scientific experiment by the US military in the 1950s. In those studies, volunteers were dressed in Arctic survival suits and exposed to bitterly cold conditions. Because it was the only part of their bodies left uncovered, most of their heat was lost through their heads.
The face, head and chest are more sensitive to changes in temperature than the rest of the body, making it feel as if covering them up does more to prevent heat loss. In fact, covering one part of the body has as much effect as covering any other. If the experiment had been performed with people wearing only swimming trunks, they would have lost no more than 10% of their body heat through their heads, the scientists add.
The researchers then decided to look at several other widely held beliefs to see if there was any published scientific evidence to support them. In many cases, they found several studies that completely undermined them. "Examining common medical myths reminds us to be aware of when evidence supports our advice, and when we operate based on unexamined beliefs," they write.
Another myth exposed by the study was that sugar makes children hyperactive. At least a dozen high-quality studies have investigated the possibility of a link between children's behaviour and sugar intake, but none has found any difference between children who consumed a lot and those who did not. The belief appears mostly to be a figment of parents' imaginations. "When parents think their children have been given a drink containing sugar, even if it is really sugar-free, they rate their children's behaviour as more hyperactive," the researchers write.
The warning that snacking at night makes you fat is on similarly thin ice, Vreeman and Carroll discovered. At first glance, some research suggests there may be a link, with one study showing that obese women tended to eat later in the day than slimmer women. But according to the BMJ article, "The obese women were not just night eaters, they were also eating more meals, and taking in more calories makes you gain weight regardless of when calories are consumed."
The researchers also have some unwelcome news for those hoping to survive the festive excesses by turning to hangover cures. After an extensive review of evidence for the curative benefits of bananas, aspirin, vegemite, fructose, glucose, artichoke, prickly pear and the drugs tropisetron and tolfenamic acid, they conclude that none has been proven to cure hangovers. "No scientific evidence ... supports any cure or effective prevention for alcohol hangovers," they state. "The most effective way to avoid a hangover is to consume alcohol only in moderation or not at all."
The team went on to show that contrary to popular belief, the Christmas plant poinsettia with it blood-red leaves is not toxic, and that suicides do not rise over the holiday period
Why Winter Hats are Unnecessary, Yet Nice to Have Around
I, for one, gladly admit that sunny Southern California has no justifiable reason to complain about its annual rainy day, specifically in relation to the experience I’ve had since deciding to spend the better part of each year in New Jersey. Nonetheless, I had a mother. And my mother, being a mother, told me to wear a hat when I went out in the ‘cold,’ because, apparently, that’s where the body loses most of its heat.
Sorry, Mom. I hate to turn this into an “I told you so,” moment, but that “fact” was exposed many years ago for the physiological fallacy that it is. In fact, an article published in the British Medical Journal (BMJ) explains that the belief was probably inspired in part by an archaic U.S. Army Field Manual that recommended covering the head, claiming that some absurdly disproportionate percentage of body heat is lost therefrom. The BMJ cites this article in the New York Times, in which the explanation becomes apparent. For whatever reason, the study from which the army manual extracted its figure was performed on subjects who were wearing arctic gear covering their entire body from the neck down. In other words, these subjects experienced the greatest amount of heat loss from their heads simply because everything else was insulated in army-grade cold gear.
A more recent study, one performed with infinitely more reasonable testing procedures, confirms results that were already pretty well known. Generally, total heat loss in the human body is proportional to the exposed surface area. Since your head doesn’t really have the same square footage as, say, your torso, your head does not dissipate heat faster than your torso does – in the absence of confounding variables, like selectively positioned insulation, that is. You shouldn’t expect more than 10% of your total body heat emission to occur through your head, in the conditions mentioned above.
However, I don’t mean to argue that you shouldn’t wear hats this winter – let’s face it, I am writing from New Jersey, after all. Even the more recent study on heat loss mentioned above noted increased core cooling rates when subjects’ heads were exposed to cold water, regardless of whether or not the subjects were wearing body-insulation. Furthermore, the writer of this article from The New York Times notes that the human head – the face in particular – is more susceptible to sensing changes in temperature than other parts of the body. Thus, protecting these areas would probably allow you to feel a little better this winter. Maybe in some cases, Mother does know best…
That being said, it’s still a scientific inaccuracy to claim point-blank that the human body loses most of its heat through the head, as there’s no physiological property that makes this so. It’s only true for those of us who have dashed out the door donning parkas and snow pants, only to realize we’ve forgotten our hats.