Keep it under your hat! Medics have debunked the heat-loss myth. Photo: Kevin Botto

It has been an enduring tenet of mountain wellbeing: cover your head, because you lose 60 per cent of your body heat through it; or 80 per cent; or 110 per cent…

Well, a pair of scientists with far greater knowledge of physiology than anyone we’ve ever met have bebunked that ‘fact’ and we now have to relegate the old head radiator story to that of myth. It seems the head is just like every other bit of the body when it comes to losing heat.

Leaving you head uncovered will make you lose no more than 10 per cent of your body heat. Here, we must hold up our (gloved) hands: we fell into the trap ourselves, claiming in a recent feature that: “Anything up to 60 per cent of your body’s heat loss will be through your head.” While technically true – 10 per cent is ‘up to 60 per cent’ – clearly that was misleading.

Here’s what Rachel C Vreeman and Aaron E Carroll wrote in this month’s British Medical Journal: “As temperatures drop, hats and caps flourish. Even the US Army field manual for survival recommends covering your head in cold weather because ‘40 to 45 per cent of body heat’ is lost through the head.

“If this were true, humans would be just as cold if they went without trousers as if they went without a hat. But patently this is just not the case.”

Now, we’re not advocating going without either trousers or hat in sub-zero temperatures on our fells and mountains. Those ears will still be stinging in the wind chill and 10 per cent is still a fair amount of heat to be losing. And it simply doesn’t bear thinking about what a touch of frostnip could do to those delicate bits of flesh if the trousers were discarded.

It’s just that, well, the whole outdoor world has been overstating the head-heat-loss case.

So, it’s a big thank-you to the pair of Indiana University School of Medicine boffins for debunking that piece of misinformation. And a slap on those camouflaged wrists of the US Army for misleading us for so long.

The long-lived error arose, according to Vreeman and Carroll, because the original data came from subjects dressed in military arctic survival suits in very cold temperatures, which led to a distortion of the results. If the subjects had been wearing only swimsuits (in the Arctic!), only 10 per cent of their heat loss would have been through the head.

The pair’s conclusion is: “If it is cold outside, you should protect your body. But whether you want to keep your head covered or not is up to you.”

Sadly, for those of us who like to over-enjoy the festive period, one of the other medical myths debunked in the BMJ article was the hangover cure. There isn’t one, unfortunately.

So forget Vegemite, bananas, fructose, borage and artichokes. The only cure for alcoholic overconsumption is not to do it in the first place.

Still, a stiff walk up a nice mountain in the cool winter air should help clear the cerebral paths a little. Now, where did I put my hat?