Do you have an unusually good tolerance for chills? Do you insist on wearing shorts even in winter? There's a fair chance you might be one of the few people who has an improved resilience to cold thanks to a genetic mutation.
A certain protein, known as α-actinin-3, found in fast-twitch muscle is absent around 1.5 billion people worldwide because they have a particular gene variant. Most people will be unaware whether they have this gene or not, but it does appear that it could have an interesting effect on the body's ability to deal with frosty temperatures.
In a new study, published in the American Journal of Human Genetics, researchers clearly show how people lacking the protein α-actinin-3 appear to endure cold temperatures better than those with the protein.
Scientists at Karolinska Institutet in Sweden and the Lithuanian Sports University gathered 42 healthy men between the ages of 18 and 40 who were asked to sit in cold water in an attempt to lower their body temperature down to 35.5 °C (normal body temperature range from around 36.5 to 37.5 °C). While their bodies were being chilled, the scientists closely looked at the electrical activity in their muscle and later took samples of their muscle to study the protein content and fiber-type composition.
They found that nearly 70 percent of the people with variant who lacked α-actinin-3 were able to maintain their body temperature above 35.5 °C, while only 30 percent of participants with α-actinin-3 were able to do so. In other words, people without the protein generally did a better job at withstanding the cold.
The research also reveals that the skeletal muscle of people lacking α-actinin-3 contains a larger proportion of slow-twitch fibers, as opposed to fast-twitch fibers. While being dunked in the cold water, people without α-actinin-3 had increased activation of slow-twitch fibers that produce heat by low-level constant contractions. On the other hand, people with α-actinin-3 had increased activation of fast-twitch fibres, which results in overt shivering.
It’s speculated that this gene variant may have sprung up when prehistoric human people started migrating to colder environments. Those with the variants were able to withstand the colder temperatures more effectively, thereby gaining an evolutionary advantage against others. Armed with this theory, the researchers believe their work could help to build on our understanding of early human migrations, as well as modern-day diseases.
"Although there are many avenues for future investigation, our results increase our understanding of evolutionary aspects of human migration," Marius Brazaitis, co-senior study author of the Lithuanian Sports University, said in a statement.
"While the energetically efficient heat generation in people lacking α-actinin-3 would have been an advantage when moving to colder climates, it might actually be a disadvantage in modern societies, where housing and clothing make cold protection less important, and where we basically have unlimited access to food, such that energy efficiency can impose a problem and result in obesity, type 2-diabetes, and other metabolic disorders."