It is winter here in the Northern Hemisphere and the temperatures everywhere are dropping. There is snow in many places and you need a pair of gloves when you go out. Are you feeling the cold yet?
- Geographical temperature differences
- About the Inuit
- How do we feel cold?
- What happens in our bodies when we feel cold?
- Why is it important to be able to feel cold?
- Why are some people more sensitive to cold than other people are?
- Can you get used to cold weather?
- Does our genetics influence how we feel cold?
- Inuit and the cold weather
Geographical temperature differences
Of course, geographical differences mean that some countries are colder than others, with the average mid-winter (January) temperatures in central Europe (Berlin, Germany, from -1.9°C to 5°C) warm in comparison to Scandinavian countries (e.g., Stockholm, Sweden, from -5°C to ‑0.7°C) or parts of North America (e.g., Toronto, Canada, from -7°C to -2.3°C). This is not cold as Nuuk, the capital of Greenland (average temperature range between -10°C and -4.6°C) or even further North in Ilulissat, Greenland, where the average temperature range is between -17°C and -10°C. Furthermore, in Iqaluit, Canada, the average January temperature range is between -30.9°C and -22.8°C [1–6].
Are feeling cold now? Not everyone feels the cold in the same way; some people seem to be more sensitive to it than others. This raises the question of whether people who live in these cold climates are less sensitive to the cold or whether they just know how to cope with it better.
About the Inuit
The largest populations of indigenous Inuit are in Greenland and parts of Northern Canada. They are also native to parts of Alaska, USA, and Chukotka, in far-eastern Russia. Previously referred to as Eskimos, the name Inuit means “the human beings” in several native languages .
Inuit live in cold, snow- and ice-bound, arctic and subarctic regions and traditional life adapted to the challenges of these regions. Traditionally Inuit were nomadic and their diet included what they could hunt or fish and they made clothing from the fur or skins, they lived in igloos made of ice-blocks in winter, and moved around using dog sleds and kayaks. Most Inuit now live in towns and cities and have access to snowmobiles and modern cold weather clothing . What has not changed, however, is the cold weather.
Before discussing whether Inuit feel the cold less than other people do, let us look at how and why we feel cold and factors that affect it.
How do we feel cold?
We sense temperature through activation of warm and cold receptors, called thermoreceptors, in our skin. If, through activation of cold thermoreceptors, impulses from the brain tell us we feel cold, we are motivated into taking action (going inside, putting on a jumper, etc.). The same is true if we feel hot (we can find shade, take off a jumper, etc.). These actions help protect our internal body temperature.
What happens in our bodies when we feel cold?
The information from skin thermoreceptors is sent to the brain where it is assessed in combination with our core temperature and factors like the water and salt content of the body or cardiovascular and immune system function. Then, processes controlled by the autonomic (involuntary) nervous system are activated to help with the internal regulation of heat production and heat loss and maintain normal body temperature.
A drop in temperature causes
- vasoconstriction of blood vessels limiting blood flow to the skin and preventing further heat loss through the skin
- shivering or thermogenesis (heat production) to increase temperature.
An increase in temperature causes
- sweating to cool the skin
- vasodilation of blood vessels in the skin to increase heat loss through the skin .
Why is it important to be able to feel cold?
Sensing changes in temperature is important to protect our bodies from extreme temperature changes. When we sense that we are cold, we can put on a coat or go indoors, thereby supporting the biological processes that keep our temperature stable. Average body temperature is around 37°C, although it may be higher or lower than this depending on age, gender and weight, time of day and amount of physical activity. It is also slightly higher in warm weather and lower in cold . The ability to regulate body temperature according to our environment and maintain an optimum core temperature (called thermoregulation) protects us from overheating and developing heat stroke (hyperthermia) or losing too much heat and developing hypothermia, both of which can have life-threatening consequences.
Why are some people more sensitive to cold than other people are?
Body shape and size
Taller, thinner people feel the cold faster due to the high skin surface area relative to their body mass and less insulating body fat. People with a higher body mass index (BMI) and more subcutaneous fat will have a warmer core temperature and retain heat for longer, but increased layers of fat mean that heat from underlying muscles takes longer to reach the skin.
Age is also important in cold sensitivity. Over the age of 60, people become less likely to notice the cold and it takes them longer to warm up.
Women are often more sensitive to the cold than men. Their increased subcutaneous fat layers compared to men keep the core warm but delay or prevent heat reaching the skin. They also have less insulating muscle than men do. Women also have changes in core temperature linked to hormones of the menstrual cycle.
People with a high metabolism generally have a higher core temperature the people with a slower metabolism. This is seen in people with an over- or under-active thyroid gland. A higher muscle mass is associated with an increased metabolism.
General health or underlying disease
In general, healthier people are better able to regulate their core temperature. The onset of fever, Raynaud’s disease, hypothyroidism and peripheral arterial disease can lead to feeling cold.
Cold sensitivity may also be related to the climate where you grew up.
Can you get used to cold weather?
It is possible to get used to cold weather, and people find ways to adapt to the cold, such as wearing warmer clothing or sleeping under thicker blankets. Perhaps more importantly, the body can adapt. It has been reported that people in arctic regions show three stages of acclimatizing to the weather:
- Reduced physiological responses to cold: reduced shivering and vasoconstriction (habituation phase)
- Increased thermogenesis (metabolic adjustment phase)
- Enhanced mechanisms to conserve body heat (insulative adjustment phase) .
This was illustrated by a small study of 14 subjects who underwent repeated cold-water immersion at 14°C for up to 3 hours at a time over the course of 20 days. The researchers found that over the course of the 20 days, participants changed from shivering to produce heat to non-shivering heat production . Despite the limitations of sample size, there is a suggestion that cold acclimatization begins relatively quickly.
Does our genetics influence how we feel cold?
It seems that it is possible to inherit an increased sensitivity to cold. A study of 894 pairs of twins found that the feeling of cold hands and feet is heritable, meaning it is genetic in origin .
Recent research found that a genetic variant (nonsense polymorphism) in the ACTN3 gene in skeletal muscle causes a lack of alpha‑actinin-3 that makes men (women were not included in the study) more resilient to the cold during cold-water immersion. The researchers found that those with the variant maintained their body temperature better during cold exposure and shivered less. These results were caused by the loss of alpha-actinin-3, leading to increased muscle tone and improving the muscle’s ability to generate heat, thus reducing the need to shiver. The variant is common and thought to cause the loss of alpha‑actinin-3 in 1.5 billion people worldwide. Moreover, researchers have suggested that there may have been positive selection of this allele due to the survival advantage for those living in colder environments [16, 17, 18].
Inuit and the cold weather
From this background, we can assume that individuals who live in arctic and sub-arctic regions have adapted physiologically to the cold and it seems likely that genetics is involved too. Indeed, scientific research supports this assumption.
A genome-wide study published in 2016 found that Greenland Inuit have a haplotype (a group of genetic variants on a single chromosome that are usually inherited together) in a genomic region that is closely related to the sequence in the Denisovan genome (Denisovans, now extinct, were a race of early humans who lived across Asia). It is thought this sequence is present in modern humans due to interbreeding between Denisovans and Neanderthals (another extinct race of early humans who lived in Europe and Asia). The authors report that the haplotype is almost entirely missing in African populations, but present among Native Americans and some Siberian populations and suggest that geographical selection of the haplotype occurred allowing ancient humans to move into colder areas. The genomic region includes two genes, WARS2 and TBX15, known to be associated with fat tissue differentiation and body-fat distribution, as well as facial morphology, stature and skeletal development. TBX15 in particular, has a role in the differentiation of the brown fat cells that are involved in heat generation (thermogenesis), this, the authors suggest, makes it a strong candidate gene for adaptation to living in cold countries [19, 20].
The ability to regulate body temperature according to our environment and maintain an optimum core temperature protects us from the life-threatening consequences of overheating or becoming too cold. We sense temperature through thermoreceptors in our skin and impulses from the brain tell us to take actions to help protect our internal body temperature. Many factors influence how we perceive cold including age, weight and gender. Inuit live in cold arctic and subarctic regions of Greenland and parts of Northern Canada as well as parts of the USA and Russia, where outdoor temperatures that are often below -10°C necessitate behaviors and clothing that support survival. People who live in these cold regions show physiological adaptations to the cold as well as genetic alterations that offer a survival advantage for these environments.
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