| Monday’s medical myth: you can catch a cold by getting cold |
| Merlin Thomas, The Conversation |
| Monday, 25 July 2011 |
| Colds are more common in the cold winter months. But does the weather have anything to do with why we get sick? These days, we use other terms such as “virus” or “the flu” to describe our sniffles because we have a fair idea of their origins. So when we call it a “cold”, don’t we also imply that the temperature outside was the cause? Growing up, my mum always said, “Put on your woolies or you’ll catch a cold!” But a winter scarf is not a surgical mask; it’s hardly going stop me inhaling a virus from other people’s coughs and sneezes. So did Mum confuse getting cold with getting a cold? She could be forgiven for that. More likely, I wasn’t listening that closely. When you think about it, many of the symptoms are very similar. Go out on a cold and frosty morning and inhale deeply through your nostrils – you do get a tingle in your nose. Take a deep breath in through your mouth and your throat feels strangely dry and coarse. Sometimes, it will even trigger a cough. If you stay out for too long in the cold, you may start shivering, your hands are cold to touch and fingers go white. You breathe faster and your heart rate picks up. All this happens as the sympathetic nervous system is activated to preserve heat. These symptoms are similar to those you experience when you have a cold. As the immune system begins its fight against the cold virus, it resets the brain’s control of body temperature. So instead of running close to 37°C, the immune system releases pyrogens, which turn up the heat and establish a new temperature at which the body will run. This is usually experienced as feeling cold because, from the brain’s point of view, you are colder than it wants you to be. So it makes you shiver, breath faster, and shuts down your peripheries in exactly the same way as it does when trying to cope with cold weather. The other confusing factor is that colds are more common in colder months and least common in summer, so they’re temporally associated with cold. When it’s cold, people are more likely to spend longer periods indoors at close proximity to others. This makes it easier for infectious droplets of mucus, which are coughed, sneezed, or passed on via hands, to transmit from one person to another. So the association with cold weather is an example of a confounding factor rather than a causal link. For example, people who carry matches are more likely to develop lung cancer. For thes same rationale, it’s still widely assumed that you can breathe in the cold, to literally catch it, so that even when you came back indoors the “cold” stays with you. Colds have been recognised as a cause of illness since the beginnings of Western medicine. In the 16th century, the term “a common cold” was widely used to denote much the same illness we experience today. Even earlier, in traditional Chinese medicine, illness was perceived as a state of imbalance between yin and yang. Yin represents the darker cooling forces, while yang are the lighter, warmer forces. In this paradigm, a cold is caused by inhaling the cold wind (a yin qi). Although we all now know that colds are caused by seasonal viruses, its hasn’t stopped us secretly feeling, in our heart of hearts, that getting cold somehow makes this more likely. A number of theories have been put forward to explain how cold weather may influence our susceptibility to viral attack. Some studies have suggested that short-term exposure to cold weather or direct chilling alters the immune system or the nose’s defences. Some viruses are killed by ultraviolet light, which is in short supply on cold wet winter days. Large studies have tried very hard to substantiate this myth. Most famous of all were performed at the Common Cold Research Unit in Salisbury, England, where thousands of paid volunteers were chilled before infected mucus was exchanged. Although much was learnt about the illness, being wet and cold appears to have little to do with it. But just because you can’t catch “the cold” doesn’t mean you shouldn’t wear your winter woollies. Perhaps the most important reason to stay warm is it allows you to venture outside and be active for longer. Most viruses are transferred and amplified in our heated indoor areas, and risks are greatest to sedentary people. So indirectly, rugging up and going outside does reduce your risk of getting a cold. Mum was right after all. |
| 欢迎光临 肝胆相照论坛 (http://hbvhbv.info/forum/) | Powered by Discuz! X1.5 |