Blog post by Hannu Rintamäki
All humans react to the cold in a same way: to minimize heat loss we first create a cooler shell around our body by lowering our skin as well as leg and arm circulation to the minimum. If this is not enough to maintain our stable internal body temperature, we increase heat production by metabolic heat production or shivering.
Our physiological and psychological responses are modified throughout the year by acclimatization, which in winter improves our cold tolerance.
Cold makes people adapt
Although we all basically respond to cold in a similar way, there is a great deal of evidence that living in cold climates makes people permanently more cold tolerant.
In the 19th century, it was found that species, including humans, tend to be taller in the North than in lower latitudes (Bergman’s rule). They also have shorter extremities, in order to minimize the exposed body surface area, and hence heat loss, in cold climates (Allen’s rule).
In the 20th century, higher metabolic rates and better aerobic fitness were measured in people living in cold climates.
Not until the 21th century were several important findings made: mechanisms of cold and heat receptors in cell membrane channels, brown adipose tissue in adult people, and a vast amount of genetic effects of living in the cold.
Long-term genetic adaptation affects the essential functions linked to cold tolerance, such as our ability to store chemical energy in body tissues and to mobilize and use energy, and our capacity to produce metabolic heat. Our circulatory adjustments are also highly sensitive and can be very strong.
One of the most significant examples of adaptation to cold winters is the leptin receptor, which is involved in the regulation of appetite, energy balance and heat production. It has also been linked to lower body mass index, less abdominal fat, and lower blood pressure, all which help protect against metabolic syndrome.
However, some genes improve heat production by increasing blood glucose levels, and promote fat storage, which in turn raises the risk of type 2 diabetes, heart disease and diabetes. Not so good.
Another interesting finding is that repeated cold exposure stimulates improved insulin sensitivity, which seems to be linked to the activation of brown adipose tissue.
It is reasonable to ask whether these capabilities, developed over thousands of years are a benefit. Or are they a burden, to people who are no longer struggling to survive in harsh climates? Perhaps they are both, and future research will bring more understanding.
At the moment, I believe that exposing ourselves – but not overexposing – to conditions that benefit these genetic capabilities could indeed be good for us.