Fat helps us acclimate to the cold

  • Article by: KIM ODE , Star Tribune
  • Updated: February 23, 2014 - 12:02 AM

Neanderthal DNA has enabled us to endure our frozen climate.

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A reconstructed Neanderthal skeleton, right, and a modern human version.

Photo: Frank Franklin II • AP file,

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Call it the 40-degree phenomenon.

Remember how Tuesday’s temperature sent us whooping in the streets? We were ready to invite pals over for a barbecue or cajole restaurants into opening their patios.

Yet that same temperature in October had us scrambling for gloves and scarves and arguing about turning on the furnace.

The difference is that by now we’ve acclimated to the cold, a transition that northerners have needed ever since cave dwellers woke up to fall’s first frost with their winter pelts still in storage.

“It’s our Neanderthal DNA,” said Dr. Kevin Fleming, who is in general internal medicine at the Mayo Clinic in Rochester. “We’re genetically equipped to handle this.”

Fleming says this like it’s a good thing — and it is — yet no one likes to think about how this shift actually works: The way to get better at withstanding the cold is by exposing ourselves to the cold.

To further an abominable image: Recent research says that our acclimating abilities are linked to the amount of brown fat we harbor.

Brown adipose tissue, or BAT, lies in deposits around our necks and clavicles, sort of like chinking in a log cabin. Once these fatty deposits are activated by exposure to cold, they generate heat, Fleming said.

Think of how our bodies react during the first cold snap. Say you’re sitting on the bleachers for your kid’s football game. Likely, you haven’t dressed warmly enough, because who wears mittens in October? By the third quarter, you’re shivering, which is your body’s attempt to generate heat. Physiologically, it helps, but psychologically, shivering makes us feel even colder.

“The only way you can generate heat without shivering is if you get more exposure to cold, which activates the brown fat,” Fleming said. Unfortunately, this heat doesn’t kick in like those chemical hand warmers, but is more gradual.

“It’s like how people who move here from the South hate it, but then get used to it after a couple of years,” he said. “Why does it take so long? Because they have to grow tissue.”

Despite this physical response, pay no mind to the folklore that blood thickens in the winter. It doesn’t, Fleming said, wondering if the old saying stems from what happens if you injure yourself outdoors. “You just bleed differently when it’s freezing.”

Summer is another challenge

Conversely, the human body also acclimates to heat.

A study last year in the Journal of Occupational and Environmental Hygiene said that older firefighters could tolerate a blaze where the heat is particularly intense more easily than younger or less experienced colleagues, who needed to stop and take a break.

This resilience translates to residents of hot climates, or to people in jobs where they’re exposed to heat stress. According to the research, those who can handle the heat are more likely to do their jobs without risking injury due to a lapse in alertness or coordination.

The human body is not endlessly adaptable, however. One climate factor especially resistant to acclimation is humidity.

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  • Homo Neandertalensis, or Neanderthal man. AP file photo.

  • Where did its genetic code go?

    So where did all the Neanderthal genetic code go? Much of it went to the grave with sterile males, who carried it on their single X chromosome, said geneticist Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “Males have only one X chromosome, so if they get a slightly bad version of this from Neanderthals, they have no other version of the X chromosome to compensate with,” he said. At least 20 percent of the Neanderthal genome “introgressed” into the genome of our European and Asian ancestors, and East Asians retained slightly more of it, an analysis said. The study found that Beijing residents with Han Chinese ancestors had the highest Neanderthal DNA rate: 1.4 percent. Los Angeles residents of Mexican descent had 1.22 percent Neanderthal DNA. In Europe, Finns had the highest Neanderthal DNA rate with 1.2 percent. Utah residents with northern and western European roots came in at 1.17 percent. And Puerto Ricans had only 1.05 percent Neanderthal in them.

    los angeles times

    THE NEANDERTHAL WITHIN

    Neanderthal genes lurk among us. Traces of the genes have been confirmed in modern humans. A look at their legacy:

    Skin and hair: Instructions related to skin and hair are as much as 70% Neanderthal.

    Immune function: Their genes seem connected to certain immune functions, allowing modern humans to recognize dangerous invaders.

    Food and survival: Genes related to such diseases as Type 2 diabetes, Crohn’s and lupus. The diabetes gene likely helped us survive food shortages, and may have proved detrimental as food became too abundant in recent times.

    news services

    Fertility: Interbred Neanderthals led to lower fertility rate.

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