It’s cold! A physiologist explains how to keep your body warm

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Whether waiting for a bus, playing outside or walking the dog – during the colder winter season, everyone is looking for ways to stay warm. Fortunately, the process your body uses to break down foods acts as an internal heater.

But when the weather is cold, some protective strategies are also necessary to prevent your body from losing its heat to the surrounding environment. As the temperature difference between your warm body and its frigid surroundings increases, heat is lost more quickly. It becomes more of a challenge to maintain a normal body temperature.

And two people with the exact same body temperature in the exact same environment may have very different perceptions. One may feel frozen while the other is completely comfortable.

But beyond the subjective experience of cold, researchers know that there are natural physiological responses to the cold as well as behavioral adaptations – like curling up! – can help keep your body around 98.6 degrees Fahrenheit and ensure you feel warm.

What your body does

Your blood courses through your body carrying nutrients, oxygen and other important biological substances. And this delivery system also brings heat produced in the muscles to the skin, where it is released.

When you enter a cold environment, your body redistributes blood to the torso, protecting and maintaining the warmth of the vital organs there. At the same time, your body restricts blood flow to the skin. By narrowing the pathways to the skin less heat can make the journey, so less is lost to the environment. And by reducing the amount of blood going to the skin – which is close to cold – you can retain more of your internal heat for longer.

Another defense strategy the body uses to stay warm is to flex muscle activity. This increases your metabolism and creates more heat. Think of a brisk winter walk when the mercury has really dipped – your teeth may be chattering and your hands and feet may shake uncontrollably as you shiver. This unproductive use of the muscles is an attempt to increase body temperature by breaking down more nutrients to stoke your internal furnace.

Differences in body size, body fat and metabolic activity affect how different people experience the cold. Smaller people with low levels of body fat lose more heat to the environment than larger people with more body fat. A larger person may have increased muscle mass, which is a heat producer, or increased body fat, which acts as an insulator to reduce heat loss. Changing these differences is not easy.

Things you can do

In order to maintain a feeling of warmth, you can manipulate your clothing, activity and food.

The most common thing people do to stay warm is to wear a coat, hat and gloves. The thickness of clothing or piling on the layers obviously helps. Winter clothing does not warm you up, but it is a way to keep the heat you are producing from dissipating into the surrounding environment.

Contrary to popular belief, the head is no greater source of heat loss than any properly covered body part. If you were to wear a warm hat without a coat, your torso would contribute more to heat loss, thanks to the way your body redistributes its blood in cold conditions. If you can keep your torso warm, you will keep the blood flow to your limbs and you can often keep the limbs, legs, hands and feet warm.

Second, being physically active causes your muscles to contract, breaking down more nutrients, which generates extra heat. This extra heat production can help maintain body temperature and the feeling of warmth. You may have noticed this in your own life if you’ve been running in place for a while or if you’ve done a quick set of jumpers when you’re out in the cold.

Unfortunately, physical activity or layers of clothing can tip the balance beyond what you need to offset heat losses. In that case, you will experience an increase in body temperature – and your body will begin to sweat in an attempt to cool down. This is a bad result, as sweat evaporation will lead to greater rates of heat loss.

Finally, eating increases the body’s heat production. The process of breaking down food is going to slightly increase body temperature. Sometimes campers will have a snack before bed in an attempt to stay warmer through the night. Although the metabolic impact of a small snack may not be huge, the tipping point between heat balance and heat loss is quite small.

You may also notice an urge to urinate – what doctors call cold diarrhoea. It is a side effect of constricting blood vessels and the increase in blood pressure as a result of which the same amount of blood has less space available to travel through your body.

And if you are the type of person who feels cold and leaves your coat on even inside, you might want to reconsider the habit. Your skin will be flushed with blood and your body will try to dissipate extra heat within. Worst of all, you might start sweating. When you go back out the door, you might feel even colder than you would have at first because the cold air lowers the heat from your skin and your sweat disappears. To stay comfortable, your best bet is to dress appropriately, whether indoors or outdoors this winter.

This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. It was written by: JohnEric W. Smith, Mississippi State University

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JohnEric Smith has received research funding from multiple sports nutrition companies. He is a member of the Dymatize Nutrition Advisory Board.

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