Have you ever seen someone out for an early morning jog in January or February wearing nothing but a t-shirt and shorts and wonder why in the world that person thought it was a good idea to forgo some warmer clothes? Indeed, some people just don’t seem to be as fazed by the cold as the rest of us.
An extraordinary new study just released by the Karolinska Institutet is offering up an explanation to this phenomenon, and it sounds like something right out of a comic book. Swedish researchers report that roughly one in five people carry a mutation providing “superior resilience” to the cold. Maybe the X-Men’s Iceman character isn’t so far-fetched after all.
These findings all come down to the protein α-actinin-3. Skeletal muscle in our bodies is made up of two distinct kinds of fibers: fast-twitch white fibers and slow-twitch red fibers. Fast-twitch fibers are more vulnerable to cold and fatigue, while slow-twitch fibers offer more protection due to their durability and energy efficiency.
Now, α-actinin-3 is only found in fast-twitch muscle fibers. But, researchers say close to 20% of the global population (about 1.5 billion people) show no signs of α-actinin-3 in their bodies due to “a mutation in the gene that codes for it.” So, these individuals have more slow-twitch fibers in their muscles, making them much more resistant to both cold weather and overall fatigue.
“This suggests that people lacking α-actinin-3 are better at keeping warm and, energy-wise, at enduring a tougher climate, but there hasn’t been any direct experimental evidence for this before,” says Håkan Westerblad, professor of cellular muscle physiology at the Department of Physiology and Pharmacology, Karolinska Institutet. “We can now show that the loss of this protein gives a greater resilience to cold and we’ve also found a possible mechanism for this.”
Importantly, study authors also say the prevalence of this genetic mutation increased quite a bit when early humans first migrated from Africa to the much colder climates of Europe.
At first, these results may make all of us long for more slow-twitch muscle fibers. However, researchers say what once served as an evolutionary advantage may offer health risks in a modern world.
“The mutation probably gave an evolutionary advantage during the migration to a colder climate, but in today’s modern society this energy-saving ability might instead increase the risk of diseases of affluence, which is something we now want to turn our attention to,” Professor Westerblad explains.
Saving more energy may sound great initially, but if one already leads a fairly stagnant lifestyle this mutation isn’t going to do them any favors. Moreover, people with no α-actinin-3 seem to find it harder to use their full strength.
“People who lack α-actinin-3 rarely succeed in sports requiring strength and explosiveness, while a tendency towards greater capacity has been observed in these people in endurance sports,” Professor Westerblad adds.
These significant conclusions were reached via an experiment including 42 healthy men (ages 18-40). Each participant was asked to sit in cold water (57 degrees F) until their body temperature dropped to 95.9 degrees F. While subjects sat in the water, researchers used electromyography (EMG) to assess electrical activity in their muscles. Muscle biopsies were also performed to investigate protein content and fiber-type composition.
That process showed that men with no α-actinin-3 had much larger amounts of slow-twitch fibers in their muscles. As participants sat in the cold water and their body temperatures adjusted, those with no α-actinin-3 did a better job of maintaining their body temperature in an energy-efficient manner. While men with fast-twitch fibers started shivering, those with the mutation showed no overt signs the cold was bothering them.
The full study can be found here, published in The American Journal of Human Genetics.