纽约时报 | 关于保暖的五个迷思:是真是假?

Five myths about staying warm in cold weather 关于保暖的五个迷思 […]

Five myths about staying warm in cold weather

1) Don’t turn a fan on


You might assume that fans are just for summer. After all, why would you want to spread air around the room in the winter? Sounds draughty. In fact many ceiling fans have a reverse setting, specifically aimed at use when temperatures are low. Heat rises of course, which means that the nice warm air above your radiators heads on up towards the ceiling, rather than where you’d most like it C at sitting height if you’re in your living room. This is more of a problem in rooms with very high ceilings. Picture a glossy office building with a tall atrium. Thermal stratification occurs, with warmer air near the ceiling and cooler air lower down where the people sit. So the idea is that if a fan is run on a low setting in reverse, destratification will take place. The nice hot air will be sent from the ceiling back down the walls into the room where it can recirculate and warm you up.


Research on this has tended to focus on workplaces where businesses are trying to keep vast buildings warm. In warehouses it’s been estimated that the correct use of ceiling fans can reduce energy use by 3% per metre of ceiling height, not inconsiderable in a building that might be 10m (33ft) tall.


Instructions for fans tend to suggest running them in reverse in winter (clockwise), in order to draw the air up, but not everyone agrees. There is some interesting unpublished research from Holly Samuelson at Harvard University from 2015.

风扇使用指南建议,在冬天应将其反方向运行(顺时针),将空气拉升,但并不是每个人都同意这种方法。2015年,哈佛大学(Harvard University)的萨缪尔森(Holly Samuelson)有了一些有趣的发现,但未公开发表。

She tested two types of domestic fan on forward and reverse settings in rooms of three different heights. The reverse setting led to warmer air down near the ground, but the forward setting that you would usually use in summer, resulted in warmer air at torso height. So, if you’d like warm feet, then put it on reverse. If you prefer the rest of your body to be warm, put it on the normal setting. She found it was even more successful if the fan was run at a medium rather than a low speed, although then of course you do risk sitting in a draught.


If you happen to have a large living room with a ceiling fan in the middle and chairs around the edge, far enough away not to feel the draught, then this research would suggest that forward mode on medium would save the most energy while keeping you warm.


VERDICT: MYTH C depending on how your room is arranged a fan on a low setting might help spread the heat around the room.


2) Alcohol warms you up


If you’ve been out in the snow, what could be better than a nip of something alcoholic to warm you up? Hipflasks have been carried in the mountains since the 18th Century and mulled wine is still popular in ski resorts today as people come off the slopes and head into a bar to warm up.


It is true that if you drink an alcoholic drink when you’re cold you will feel as though you’re getting warmer and you’ll look as if you are. The alcohol sends blood towards the surface of the skin, making you flush. If you touch your face it will feel hotter. The problem is the blood has moved away from the main parts of your body, so in fact your core temperature drops.


The good news is that the discomfort starts to lessen and if you’re now indoors a slight initial drop in core body temperature won’t matter. The problem is that if you’re staying out in the cold the effect of blood moving to the skin is not enough to keep you warm for long. Or if you drink a lot and then go back out into the cold, you could put yourself at risk. Alcohol can reduce the body’s natural shivering response and dampen your perception of cold.


Combine this with the impaired judgement that of course goes with being drunk, and you can see why people sometimes end up in dangerous situations. We’ve all seen the stories of people who fall into icy ditches on their way home from a bar in the freezing cold. Figures from the US show that, in a decade, 10% of deaths due to hypothermia involved alcohol consumption.


VERDICT: HALF TRUE C it warms your skin which gives you the sensation of feeling warmer, but your core body temperature can drop. In excess it can increase your chances of hypothermia.


3) Don’t sit on the radiator or you’ll get piles


This is a myth that’s been around for a while. Another is that sitting on cold surfaces gives you piles.  Haemorrhoids or piles are itchy, bumpy swellings that develop from the cushions of tissue lining the anal canal. They affect as many as 50% of people at some point of their lives.

这是一个流传甚广的迷思,另一个是坐在冰冷的东西上也会让你得痔疮。痔疮是肛肠内壁组织产生的凹凸不平、发痒的肿块, 50%的人们都在生命中某个时段受此影响。

Cooling the region can give some people relief, but there’s no evidence that warm temperatures cause them or make them worse. In fact a German study found that people who had a bath at least once a week (which presumably would be hot) had a lower risk of developing piles. (The study can be found here, but be warned that it contains graphic images).


People are at higher risk if they often have constipation and strain when they go to the loo.


VERDICT: FALSE  C sitting on radiators doesn’t give you piles. The best way to lower your risk is to eat plenty of fibre such as vegetables, cereals and nuts, avoid becoming overweight and drink water.


4) Don’t go out with wet hair or you’ll get a cold


My guess is a lot of us were told this by our grandparents. I certainly was. The name “cold” even suggests you catch it by going outside in low temperatures. The illness is of course caused by a virus and unless you catch that virus, you can’t develop a cold. But could getting chilled make you more susceptible?


In research where volunteers’ temperatures were lowered before exposing them to a cold virus, some studies found the shivering group were more likely to develop a cold, others that it made no difference.  But Ron Eccles from Cardiff University in the UK tried something different.

有研究发现,当先把志愿者处于低温下,再把他们暴露在感冒病毒下,打颤的小组更可能着凉,其余人则没有分别。但英国卡迪夫大学(Cardiff University)的埃克斯尔(Ron Eccles)则做出了不同尝试。

People had to sit with their feet in cold water for 20 minutes, before returning to their normal lives. The control group kept their shoes and socks on and simply sat with their feet in an empty bucket for 20 minutes. Five days later twice as many people in the cold water group said they now had a cold. It should be said that the study did rely on the volunteers’ own assessments.


But why should having wet feet or maybe wet hair make you more likely to catch a cold? One suggestion is that because when you’re feeling cold the blood vessels in the nose and throat constrict, meaning that fewer infection-fighting white blood cells reach your nose and throat to tackle the virus.


Others suggest that people simply get more colds in winter because they stay inside together and pass their germs around more easily. When Anice Lowen from Emory School of Medicine in the US studied how easily the flu virus passes from one guinea pig to another, she found the warm temperatures with low humidity (typical of a centrally heated house in winter) were ideal circumstances for passing on the infection.

另一猜测则是,人们容易在冬天感冒单纯是因为他们聚在室内、更容易互相传播病菌。当美国埃默里医学院(Emory School of Medicine)的洛文(Anice Lowen)研究流感病毒是如何轻易地在豚鼠之间传播时,她发现低湿度、温暖的环境(特别是冬天中央暖气或空调的房子)是引发感染传播的最佳场所。

VERDICT: MORE DATA NEEDED - going out in the cold with wet hair won’t give you a cold, but it’s possible that if you have already picked up the virus your body might find it harder to fight it.


5) Always wear a hat because you lose the most heat from your head


Obviously it makes sense to cover up well if you’re heading out into the snow, but is it true that it’s especially important to keep your head warm?


Hardy volunteers have taken part in plenty of unpleasant research on this in the hope of finding some answers. In one study Thea Pretorius from the University of Manitoba in Canada gave volunteers drugs which prevented the body from shivering. Then they were lowered into cold water wearing scuba tanks for breathing. They wore dry suits, socks and gloves or just a swimming costume. Sometimes their heads stayed above the surface of the water. At other times they were completely submerged.

勇猛的志愿者会为了找出答案而参加许多令人不适的研究。加拿大马尼托巴大学(University of Manitoba)的比勒陀利乌斯(Thea Pretorius)在一项研究中让志愿者服用抑制身体颤抖的药物。然后这些志愿者戴上潜水氧气设备,浸入冷水中。他们有人穿着干式潜水服、袜子以及手套或仅穿着泳装。有时他们的头会浮出水面,其余时间他们完全在水下。

If they were submerged but wearing the dry suit, their heat loss was mostly from their heads, but they lost only half as much heat as those in swimming costumes with their heads sticking up above the water. Since they were losing heat almost entirely from their bodies, this shows we lose more heat from our bodies than from our heads.


It is also true that if the body is insulated, but the head is exposed to the cold, the body’s core temperature still drops faster than you’d expect, possibly because we don’t shiver if only our head is cold and the reason we shiver is of course to warm us up. Also there are a lot of blood vessels on the scalp close to the surface of the skin, so if blood is cooled as it passes through the scalp, it can then cool the rest of the body as it passes through.


But this concerns the rate of cooling, rather than the lowest temperature your body reaches. When it’s freezing outside, what usually matters to you is how cold you end up. So the ideal is to keep  the rest of your body and your head well covered.


VERDICT: TRUE that it’s a good idea to wear a hat if you want to keep warm, but FALSE that you lose most heat from your head.


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