Cold and the Human Body
Your teeth chatter, your body shivers and despite all efforts, you can’t prevent it. The tiny hair on your body stand upright and try desperately to function as an insulating fur. Your skin looks bloodless and feels cold. All these reactions are an attempt by your body to preserve heat, although not a very successful one. Humans are well equipped to lose heat, but are less efficient in retaining it. Are we all meant to live on a tropical island?
Your body’s reaction to heat loss is involuntary and driven by the hypothalamus, the tiny gland in the brain acting as a thermostat (see Chapter Four, ‘Heat’). The hypothalamus is very sensitive to any temperature variation in your body. Even a small drop brings the temperature regulation mechanisms into action: blood vessels in the skin constrict to prevent excessive heat loss and muscles shiver to create heat.
The hypothalamus is a cruel gland, though. Its only concern is to keep the vital organs at an acceptable temperature, and couldn’t care less if your toes or fingers became icicles. All of the thermoregulation mechanisms are designed to protect the core. But if the system fails or becomes overwhelmed, cold-related illness or death is the consequence.
Every person reacts differently to thermal stress. Age, fitness level and underlying diseases play a major part in someone’s reaction to cold.
The best way to get through a winter is to eat as much as you can, grow a thick winter coat, reduce your body temperature and find a hole in the ground where you can hibernate. Too easy for some animals, but not for us humans who don’t acclimatize to the cold as well as we can to the heat. Nevertheless, repeated cold exposure does train the few defences to function more efficiently.
Since the body doesn’t want to adjust to the cold very well, behavioral responses become the most important factors. Shelter and clothing protect from the cold.
Eating high-energy food will increase the heat production, as will exercise – active muscles produce up to three-quarters of the total body heat, which stimulates the metabolism and further heat production. In fact, intense exercise and work can produce enough heat to maintain the desired body temperature under very cold conditions. Unfortunately, you can’t sustain heavy physical activity for long periods and you will eventually lose heat.
Shivering is an involuntary muscle movement with the aim to create heat. With a strong will you can stop the action, but not for long. If you don’t work your muscles, the body will do it for you. Extreme shivering can increase heat production by up to five times.
This bodily function does have its drawbacks. Muscle action requires fuel in the form of high-energy food. Without additional energy supply (eating), your body will soon be depleted of its reserves and become fatigued – now there’s an excuse for some indulgence. Another negative effect of increased muscle activity is an increase in blood flow. More blood is diverted away from the core to the muscles, so heat loss is accelerated.
You can’t survive on air and love alone. Even if you could, would you want to miss the pleasure of eating a chocolate cake topped with fresh strawberries? Oh no! Think of all those calories. They are good for something, though. They burn in the muscles, creating heat, and some of the excess deposits as an insulating layer of body fat.
Metabolism is the term for, among other things, the chemical process of digesting and absorbing food. When you eat (ingest) the cake, your stomach and intestines digest the delicious meal and create heat in the process. A good meal gives you a warm feeling in your belly. Absorbed nutrients are sent to the cells of all body parts, including the muscles, which then generate heat when they become active for a purpose or when they shiver involuntarily.
It is no coincidence that your core body temperature is ideal for the metabolic process. If the temperature drops, however, the chemical reaction slows down. To compensate for the drop, your metabolic rate increases slightly. Consequently, during cold conditions, the body requires more energy-rich food to support the body in its fight against the cold.
Your skin is ‘red hot’ when the body needs to get rid of excess heat. On the other hand, your skin looks pale and feels cold when the body tries to preserve heat. The blood vessels in all the non-essential areas tighten (constrict) on command and limit the amount of hot blood that can reach the skin, thus preventing heat loss. The constriction can be so severe that almost no blood circulation exists in the non-essential body parts.
Your hands and feet are particularly vulnerable to this process. They may lose their agility and simple tasks, such as typing or opening a door with a key, become almost impossible. The cells in your muscles and skin, however, can’t survive for long without some fresh blood supply. Occasionally the blood vessels will open up and allow some warm blood to reach the extremities. These pulses become less frequent and stop completely if the cold exposure continues.
Cold feet and cold hands are not necessarily a sign of poor blood circulation. It is the body’s natural way of preserving heat. Acclimatized persons, and in particular women, manage this system quite well. Cold water immersion tests have revealed that skin temperatures of women were lower and the core temperatures remained higher than that of men.