What the cold really does to your body
Quick, we’re having a cold snap. Cue nationwide alerts to stay in, crank up the central heating and stay warm. We know it comes around at least once a year, but we never seem to be prepared.
This time, though, the big freeze seems to be even more fierce, as forecasters are predicting that we could see the coldest January night in 15 years. They’re predicting extreme lows in Scotland and northern England, even chillier than our Nordic neighbours.
But the difference is that other countries with longer cold periods, such as Finland and Sweden, know how to dress to go outside and how to stay warm at home. “Our cold snaps are so brief that people don’t invest in the appropriate clothing. Triple glazing on houses is also much more common in Scandinavia,” says Dr Clare Eglin, a lecturer at the University of Portsmouth who specialises in human physiology in extreme environments.
So how does the cold really affect our bodies and how can we stay safe? Read on.
What the cold weather does to your body
It’s important to take the warnings seriously because a cold snap, however brief, will have the same physiological effect as those in more frequently colder climates. According to the ONS there are between 20-30,000 excess winter deaths, with the majority occurring among people aged over 75.
The cold weather affects various parts of the body including:
Blood vessels
When we enter a cold environment, our body will try to conserve heat, and it will do this by narrowing the blood vessels near the skin. “So vasoconstricting reduces the amount of heat we lose, which is good because it maintains our core temperature, and for mild conditions that’s quite enough,” says Dr Eglin.
Shivering is our body’s way of trying to produce heat as our core temperature drops.
However older people are particularly at risk as their bodies don’t respond as well in defending their body temperature. “Their blood vessels don’t constrict as well, and because of the decline in muscle mass generally they aren’t able to produce as much heat by shivering,” says Dr Eglin.
The heart
The main health risk posed by the cold is that when the coronary arteries narrow there is an increased risk of heart attack. “Hence the number of people who die while shovelling snow,” says Prof Anthony Heagerty, head of University of Manchester’s Medical School. The effort increases oxygen demand to the heart. “And in people with furring of the coronary arteries, the extra cold-induced narrowing cannot be achieved, causing malignant heart rhythms to occur.” So for those with underlying cardiovascular problems, taking care in the cold is more important.
While deaths associated with hypothermia are relatively rare, those from heart attack or stroke in the cold aren’t.
Muscles
Everyone knows the feeling of struggling to do something when their hands are cold.
As we get colder our muscles cool and lose their function.“We see a decrease in force and what’s most noticeable is a loss in dexterity because the fluid in the joints becomes more viscous and it makes it more difficult to move,” says Dr Eglin. “The nerves are also not conducting as quickly, so your response time is slower.”
The lungs
A cold snap could increase people’s chances of cold-induced asthma.
“Those living with respiratory conditions are at an increased risk from seasonal diseases because of their lowered immunity,” says Dr Sandy Connell, medical director at MAC Clinical Research. “The cold air is often dry, which can irritate the airways of those living with respiratory problems by increasing the amount of mucus, worsening wheezing and coughing.”
However there’s no evidence that cold per se increases the chances of getting a lung infection, says Dr Eglin. “The issue is that you tend to stay indoors where it’s more crowded and are therefore more likely to get an infection just from being around other people,” she adds.
Blood clots
The cold increases mortality from arterial thrombosis (aka blood clots). “Vasoconstriction results in body fluid shifts and increased urine production (cold-induced diuresis), which leads to an increased likelihood of blood clots,” says Prof Tipton. The elderly, who have less healthy endothelial (cell tissue) lining, are more likely to form clots.
Fluctuations in temperature can increase risk of clotting, says Prof Mark Whiteley of The Whiteley Clinic: “When people enter a warm, central-heated building after being out in the cold, this can also cause thermal stress to the body, making it harder to maintain a constant temperature. This thermal stress can have a direct effect on the viscosity of the blood, making it stickier and more likely to clot.”
Immune system
“There is some evidence that the stress of a short exposure in cold water may prime the immune system,” says Prof Mike Tipton, an expert in extreme environments who teaches at the University of Portsmouth, “but the definitive studies in this complex area await completion.” There are contradictory findings. Research into whether cold temperatures lower immune function needs more work, but Dr Eglin says: “Anything that puts a severe strain on the body, for instance extreme exercise, is likely to impair immune function.”
Prof Heagerty adds: “Contrary to perceived opinion, the cold often destroys viruses.” However, because people tend to gather together to stay warm this can result in increased spreading of infections indoors.
How cold is too cold?
When it comes to what could be considered a dangerous temperature, Dr Eglin says it depends on what you are doing and what you are wearing. “If you are wearing minimal clothing, you can start shivering in quite mild conditions of about 15C.”
Conversely, she says if you’re exercising hard and you have good clothing on: “You will be fine in -10 or -15. It really depends on what you are doing and how long you are there for.
How to stay safe
Knowing your physiology is key to keeping warm, comfortable and safe. Someone who is small, thin and with little muscle mass will cool faster than someone who has either a lot of muscle mass or fat mass. “A lot of insulation basically,” says Dr Eglin.
Expert tips for staying safe during this cold snap:
If you do get cold, increased physical activity as well as warm clothing and environment is key. “However, for the elderly we wouldn’t want to suggest they start doing a lot of exercise to warm themselves up,” says Dr Eglin. During a cold snap it is vital to check on elderly relatives.
Avoid cooling of the skin in the first place. “Don’t wait until you’re outside to put on your coat, hat, scarf and gloves,” says Prof Tipton. It is also important to remain hydrated.
Ideally, your home temperature should be about 20C, says Dr Eglin. “But if you’re prepared to wear thick jumpers and slippers with a couple of layers on your legs you can get away with it being a bit colder.” If you are worried about heating bills, she says: “Choose to just heat one room and keep the others a bit cooler.”
