For generations, parents have been shouting the same warning to children dashing outside without a coat or with wet hair in freezing winter weather: ‘You’ll catch your death of cold.’
But is it just an old wives’ tale, or can you really become ill simply from being exposed to a sharp drop in temperature, even for only a few minutes?
With the clocks going back this weekend to mark the end of British Summer Time, and some experts predicting the worst winter in 30 years, the affect of cold weather on the nation’s health is a significant question.
The ‘old wives’ tale’ about wrapping up warm — particularly around the head — to avoid illness may have been right all along
Prolonged exposure to cold — usually through poorly heated homes — kills an estimated 40,000 people in the UK every winter. Many die from heart attacks or strokes, triggered by sustained exposure to low indoor temperatures (18c or less), which makes their blood vessels constrict as the body tries to preserve its core temperature of around 36c to 37c.
This means the heart has to pump harder to force blood through narrowed blood vessels, driving up blood pressure and increasing the chances of death in those with existing heart problems.
But what has been less clear is whether simply popping out without a coat, or with wet hair, during cold weather puts healthy people at risk.
For many years, the rise in cold and flu instances during winter has been almost entirely attributed to the fact that we spend more time indoors in each other’s company — giving viruses more opportunity to spread between us.
Now, while experts think this ‘crowding’ plays a part, a much bigger factor is the effect a sudden drop in air temperature has on the body’s ability to fight off invading viruses.
A landmark study at Yale University, in the U.S., found that rhinoviruses — which cause the common cold — reproduce much more effectively when temperatures in the nasal cavity suddenly drop (in this case to around 33c from the usual body temperature of 37c).
This drop in temperature occurs in extremities such as the nose, when going from a warm house to the cold outside.
The 2015 study on mice revealed that viruses flourish at lower temperatures partly because the body’s immune system is less able to produce the proteins needed to destroy the invading organisms when conditions are cooler.
Drop in temperature occurs in extremities such as the nose, when going from a warm house to the cold outside
In the Proceedings of the National Academy of Sciences of the United States of America, the researchers wrote: ‘In general, the lower the temperature, the lower the immune response to viruses.’
In other words, the ‘old wives’ tale’ about wrapping up warm — particularly around the head — to avoid illness may have been right all along.
‘We know that when people spend more time indoors together, bugs spread,’ says Professor Ron Eccles, from the Common Cold Centre at Cardiff University. ‘But I don’t believe that’s the only reason for the increase in winter illness.
‘Cold air makes the blood vessels throughout the body, including the hundreds of tiny vessels in the nasal cavity, constrict. This reduces the amount of blood — which delivers the infection-fighting immune cells — flowing into the area.
‘This could be another reason why going out in the cold puts you more at risk, assuming you are actually carrying the cold virus already.’ Standing still in the cold will increase the risk further, he adds.
‘It’s worse if you are stationary as you are not generating body heat, which keeps the blood vessels dilated and the nasal temperature higher.’
A drop in temperature also slows down movement of the cilia, tiny hair-like cells in the nasal cavity which transport mucus, and the bacteria and viruses it traps, out of the nose.
Viruses and bacteria thrive in this moist environment and, if they are not quickly ‘moved along’ by the swaying of the cilia, they can gain a foothold and cause an infection.
Professor Eccles believes there is a good reason for the age-old advice about wrapping up, as our ancestors were much more exposed to the elements than we are today as they travelled by foot or horse and would have been acutely aware of the affect cold weather could have on their health.
He advises: ‘Cover your nose and mouth loosely when going into the cold, especially if you are prone to asthma or chest infections. This warms the air as it’s inhaled.’
Professor Ian Pavord, a specialist in respiratory medicine at Oxford University, says cold air exposure is a common trigger for wheezing and breathlessness in people with asthma due to something called hyperresponsiveness. Put simply, their lungs are much more sensitive to a sudden change in temperature than a healthy person’s airways.
‘Scandinavian people deal with the cold a lot better than we do, by always wearing warm clothes, especially woolly hats, because the body loses most of its heat through the head,’ says Professor Pavord.
Going out with wet hair in winter is ‘a complete no-no’, he warns, as the head loses heat rapidly. The body also starts to lose heat, which makes the head even colder, and the brain reduces blood supply to any part of the body not considered essential, such as the nose, so it can maintain the temperature of vital organs.
It has also been found to trigger painful sinuses, as well as posterior eye pain — a type of headache involving a sharp, temporary pain behind the eye.
A study in the journal Medical Hypotheses in 2012 revealed that this is all to do with the brain’s automatic thermal regulation system, designed to protect the brain against extreme heat or cold.
Experts from the GATA Haydarpasa Training Hospital in Istanbul found that the double whammy of wet hair and freezing conditions causes blood vessels in the skull to dilate, triggering a rush of warm blood through the tiny blood vessels in the head, which can result in severe, sharp pain.
But it’s not all bad news. In fact, popping outside for an hour or two on a cold day could potentially help protect against type 2 diabetes.
A 2017 study at Maastricht University in the Netherlands found that frequently moving from hot to cold speeds up the body’s metabolism — the rate at which it burns calories — and improves sensitivity to the hormone insulin by more than 40 per cent.
If the body becomes less sensitive to insulin, or if it produces less of the hormone, this can lead to a build-up of glucose in the bloodstream and type 2 diabetes.
In tests, the scientists found that sudden exposure to colder temperatures for ten days in a row had as powerful an effect on patients with type 2 diabetes as some commonly used medicines.
How our bodies have changed over time. This week: The vanishing arm muscle
Put your arm on the table palm face up. Touch your thumb to your little finger and flex your wrist. Can you see a band rising in your wrist? If so, you are one of the 80 per cent or so of the population who still has the palmaris longus muscle, which runs from the arm to the wrist. Don’t fret if you don’t have it, as it has no obvious purpose: it’s thought to have become largely redundant since humans developed opposable thumbs. In fact, surgeons often graft this muscle elsewhere in the body following disease or trauma.
Quite why some people still have the muscle is a mystery: ‘I suspect it’s because there was no evolutionary imperative to get rid of them,’ says Dr Michael Berthaume, a bioengineering research associate at Imperial College London.
Storing up trouble
The way you handle food can have effects for health. This week: Buy green tea in small packets
If you’re an infrequent green tea drinker, you could find the healthy compounds for which you buy it have dramatically declined by the time you brew up.
Advised to buy small packs of green tea and keep them in an airtight tin. And use bottled water rather than tap to make your tea, as other research showed this doubled the epigallocatechin gallate content
A study in the Journal of Food Science found that levels of epigallocatechin gallate, the main antioxidant, which is thought to reduce inflammation and prevent cell damage that leads to disease, declined by 28 per cent within six months; other antioxidants fell by as much as 51 per cent.
Buy small packs and keep them in an airtight tin. And use bottled water rather than tap to make your tea, as other research showed this doubled the epigallocatechin gallate content.