How Do Frogs Survive the Cold? By Freezing


Credit: iStock

They aren’t moving. They’re not responding to touch or light. Their hearts aren’t beating. They’re no longer breathing. Their skin is ice-cold and hard to the touch. By that description, you probably don’t think I’m describing living things. However, there are some animals that survive like this because of a process called freeze tolerance.

Unlike mammals, whose bodies are always working to maintain a constant temperature, cold-blooded animals (ectotherms) are at the mercy of their environment. As a result, when the temperature plummets, they have to come up with a physiological means to survive the bitter cold winters.

Bugs and amphibians are the freeze-tolerant animals researchers study most often. Among amphibians, a few select frogs show a clear freeze-tolerance response. Large amounts of their bodily fluid freeze into ice particles to help them make it through the winter.

The physiological changes that prepare freeze-tolerant animals for cold weather begin as the temperature drops, but they don’t happen overnight. These animals distribute substances called cryoprotectants, which allow them to get colder than freezing while shielding them against dehydration and other cell changes that can occur when ice forms. Once frozen, the animals can withstand temperatures ranging from 32 to -22 degrees F, depending on the species. Freeze tolerance can last from weeks to months. Cycling through this process is a must for any frog that wants to see the next summer.

However, thawing may be just as important as freezing. Freeze-tolerant animals likely go through several freeze-thaw cycles, during which the distribution of cryoprotectants and tolerance to the cold increases. This suggests that the cryoprotective process isn’t finished after the first freeze and is a cumulative process as the winter grows colder. When spring arrives and the weather returns to consistently above-freezing temperatures, the animals thaw, their hearts start beating again and they continue on without negative effects.

Scientists want to learn more about freeze tolerance from the animals that do it so well. In case you missed it, humans can’t freeze and thaw themselves. By studying the physiological changes in freeze-tolerant species, researchers can apply this work to mammals, such as by storing organs for later use and keeping cell lines healthy while in storage. Studying an “ideal” organism that has overcome a functional problem allows scientists to better understand those problems in mammals. Therefore, comparative physiologists continue to research the unique traits of various organisms to understand how evolution has already handled these challenges.

Brian StogsdillBrian Stogsdill is a graduate student at Wright State University, in Dayton, Ohio, currently finishing his doctorate in biomedical science. Stogsdill researches freeze tolerance and aquaglyceroporins (a family of proteins that conduct water). 

Go Ahead and Scratch … Your Brain Is Telling You To

Itchy and dry skin

Credit: iStock

Winter is here, and for much of the country, it’s going to stick around for a while. When exposure to frosty air and the constant hum of the heat pump continue for too long, you may end up with dry, itchy skin. We know that scratching an itch feels good, but why?

Researchers studied brain activity in two groups of volunteers. One group had chronic itching problems, and the other did not. The chronic itch group had more activity in the area of the brain involved with movement than the non-itchy group. This boost in activity means their brains were “wired” to scratch.

The non-itchy volunteers were then treated with an irritant that made their skin itch. The research team found that when the healthy volunteers scratched an itch, the reward center in the brain lit up. In other words, scratching feels good even if you don’t have a chronic skin condition.

Slathering yourself with moisturizer and drinking more water can help hydrate the skin—your largest organ—and keep winter itches at bay. But sometimes you just want relief from a good—yet gentle— scratch. Now you know that your brain is giving you permission to indulge.

Erica Roth

Bring on Winter! (But Stay Safe and Healthy)


girl playing on a winter walk

Credit: iStock

Winter officially begins next week with the winter solstice—the day of the year with the fewest hours of sunlight—on Dec. 21. With the cold weather and shorter days, you might be tempted to curl up under a blanket until the spring thaw. Whether you plan to hibernate or get outside to enjoy the chill, we’ve got some good reads about how our physiology responds to the cold weather.

Check out these throwback posts featuring cold weather tips to help you stay safe and healthy during the coldest months:

Have fun, be safe and take note of how your body adapts to the season!

Stacy Brooks and Erica Roth



Shhh … I’m Hibernating!

Bear nest

Man crawling out of uninhabited bear hibernating den (not recommended). Credit: IStock

As the days grow shorter, many animals, such as bats, bears and bees, begin getting ready to hibernate. It’s a process that allows animals to spend the winter months conserving energy by reducing metabolism, oxygen consumption and body temperature. So why don’t humans do it, too? Well, a new study suggests that some humans—specifically those with chronic fatigue syndrome (CFS), which affects more than 2.5 million people in the U.S.—may be doing something similar to hibernating.

People with chronic fatigue syndrome experience extreme fatigue. But this is not your run-of-the-mill kind of post-holiday exhaustion. It is severe fatigue that does not get better, even with sleep. People with CFS may also experience issues related to memory and headaches. It’s not clear why people develop the disorder, but some theories point to infections, exposure to chemicals or stress as possible causes.

The new study, published in the Proceedings of the National Academies of Science, looked at specific molecules (metabolites) that are byproducts of energy production (metabolism) in the blood of people who have CFS and healthy people who do not have the disease. The researchers found that people with the condition had 80 percent fewer metabolites compared to the healthy control subjects. Those with chronic fatigue syndrome also had some impairment in the way their metabolism functioned. The findings suggest a less active metabolism in people with CFS similar to metabolic activity seen in animals that hibernate. Reduction in metabolic state is thought to be a defensive strategy all humans can use to cope with situations in which environmental or other stressors are present. The problem for people with CFS is that this defense mechanism stays turned on, slowing metabolism—and draining energy—on an ongoing basis.

What’s great about this study is that researchers and clinicians finally have a set of chemical markers in the blood that they can use to test people for CFS. The hope is that by understanding what’s going wrong, metabolically speaking, a treatment can be developed.

Karen SweazeaKaren Sweazea, PhD, is an associate professor in the School of Nutrition & Health Promotion and the School of Life Sciences at Arizona State University.

Running a Thousand Miles Can Be Exhausting. How Do Iditarod Sled Dogs Do It?

View of sled dog race on snow

Credit: iStock

Have you ever had a morning where you just did not have the energy to go out for your five-mile run? What if you woke up in New York City and had to run to Miami? That is the distance Alaskan Huskies run every year at the annual Iditarod sled dog race. How these amazing canine athletes accomplish this feat is interesting to scientists because it provides insight into how human performance can be maintained in challenging conditions.

Muscles get energy to exercise from glucose (sugar) and fats stored in the body. Muscles use oxygen from the air to transform the two into energy. Scientists originally assumed that the Alaskan Huskies used fat to sustain long periods of exercise. Huskies are fed a diet rich in fat, and the body stores fat in greater quantities than glucose. However, a recent study found that the dogs actually used glucose to sustain exercise and that the glucose was made from a part of fat called glycerol. The dogs took advantage of their fat stores, but they used the fat stores to make glucose.

Why go through the trouble of turning a part of fat into glucose rather than using fat as is?  That answer is not entirely clear yet, but one possibility is that the dogs typically run the Iditarod at an average of 10 miles per hour, or six-minute miles, while pulling a sled. Muscles prefer glucose to fuel intense exercise because they can get more energy out of it for every molecule of oxygen breathed in. Sustaining such high speeds while pulling a load may require the use of glucose over fat. This is not to say that fat is not important for the dogs. As mentioned, the dogs use the fat, just not directly, and fat is good fuel during rest periods and recovery between running.

The Alaskan Huskies were bred to perform these amazing endurance feats, but we don’t know yet if human muscles can invoke the same rate of fat-to-glucose conversion processes to fuel exercise of such long distance. However, humans performing at such high speeds for prolonged periods would most likely need to do this same type of conversion.

Next time you’re not up for your morning run, channel your inner sled dog: Five miles really isn’t that bad.

Benjamin Miller, PhD, is an associate professor in the Department of Health and Exercise Science at Colorado State University. He co-directs the Translational Research in Aging and Chronic Disease (TRACD) Laboratory with Karyn Hamilton, PhD.

Ben Miller with sled dog

Dr. Miller with study participant.

Don’t Be Cold-Hearted: Understand and Protect Yourself from the Cardiovascular Risks of Cold Weather

Shoveling Snow

Credit: Getty Images

Winter storms, like those that hit the East Coast in January, are often followed by sad reports of deaths from heart attacks related to winter weather. These reports often seem to be isolated incidents, but emerging evidence reveals a clear association between winter temperatures and heart attacks, particularly severe heart attacks. Recent research demonstrated that for every 18-degree drop in outdoor temperature below 86 degrees Fahrenheit, the risk for a severe heart attack increased by 7 percent. That means the risk of a heart attack is 28 percent higher at freezing temperatures. What accounts for the increased risk with cold weather?

There are a number of factors that raise a person’s chance of having a heart attack, but many heart attacks ultimately arise from an inability to provide enough oxygen to the heart. This can cause permanent damage to the heart and, if severe enough, can lead to death. In response to cold temperatures, the heart begins to pump more blood with every heart beat, and blood vessels in the limbs narrow (constrict). These physiological responses coupled with cold weather-associated activities such as shoveling snow increase the heart’s demand for oxygen-rich blood. In healthy individuals, this demand is readily met by increasing blood flow to the heart, but this increase is often blunted in individuals with cardiovascular disease or risk factors. Men older than 55 are twice as likely as women to experience snow-related heart problems, especially if they have a family or personal history of cardiovascular disease.

How can we use this information to protect ourselves? Some practical tips:

  • Understand your own cardiovascular risk and family history.
  • Maintain your preventive health care throughout the year by staying physically active, eating a balanced diet and having annual check-ups with your doctor.
  • Dress appropriately for work and play in the cold to limit heat loss and its stress on the heart.
  • Remember that the average shovel of snow weighs at least 10 to 15 pounds. Repetitive shoveling of these loads is a dangerous level of exertion for someone with cardiovascular risk factors, so buy a smaller shovel and take regular breaks.
  • Pay attention to early signs of a cardiovascular event—chest pain, dizziness, shortness of breath—and stop immediately if they occur. If symptoms persist, seek medical attention immediately.

If knowledge is power, then the research provides the power to protect us from heart attack risk in cold weather. Think this through the next time a winter storm approaches, and spread the word to help reduce snow-related heart attacks in your community.

Shawn Bender, PhD

Shawn Bender, PhD, is a research health scientist at the Harry S. Truman Memorial Veterans’ Hospital and an assistant professor at the University of Missouri.

Stack the Deck against the Flu

Golden Retriever dog cold

The Flu is Ruff!

Flu season: It’s the time of year when many of us become acutely aware of anyone sniffling and sneezing nearby. We hope to avoid a brush with the virus, which can leave us feeling awful for a few days or a week or two, causing us to miss work and be unable to take care of our families. And in severe cases, it can lead to hospitalization or death.

Influenza, commonly known as the flu, is a contagious virus that attacks the respiratory system. The symptoms—fever, coughing, runny nose, sneezing, fatigue—come on quickly and can hit you like a ton of bricks. More severe than the common cold, the flu can be very dangerous to certain groups, including infants, pregnant women, the elderly and people with compromised immune systems.

When an infected person coughs, sneezes or talks, he or she can spread the virus through the air. Uninfected people may then inhale the virus into their nose or mouth—areas where the virus can take up residence, infecting a person’s cells and making copies of itself (replicating). The more the virus replicates, the sicker the person becomes. The flu virus can also be introduced to the nose and mouth by touching surfaces where the virus is—think door handles, elevator buttons and sink faucets—and then touching the face.

So what can you do to stay flu free? Recent research suggests that estrogen may lend women extra protection against the virus. But to give yourself the best chance of staying healthy through flu season, the Centers for Disease Control and Prevention (CDC) recommends several strategies, including:

  • getting the flu vaccine each year,
  • washing your hands frequently,
  • cleaning and disinfecting surfaces that may be contaminated with germs, and
  • avoiding touching your face with your hands.

Also, remember that the activities that keep you and your immune system healthy throughout the rest of the year—eating a balanced diet and getting enough sleep and exercise—may help you ward off the flu, too. Learn more about the flu on the CDC website.

Stacy Brooks

Too Cold Outside? Try Out Polar Mammals’ Methods of Staying Warm

If temperatures in the teens (or the 50s for the warmer climates) make you grumble, be glad you’re not a mammal living in the Arctic or around Antarctica. These animals face much colder air temperatures of -40 to -76 degrees Fahrenheit. While humans bundle up with thick sweaters and jackets to get through the winter cold, mammals such as seals, penguins and polar bears stay warm with blubber, feathers and fur. How do these materials keep the arctic chill out?

Polar Bear

Credit: Getty Images

The ability of a material to insulate depends on how easily it lets heat pass through—a property called thermal conductivity. Fat has a low conductivity, which means it slows heat getting out and helps keep heat in. Marine mammals such as whales and seals have a layer of blubber beneath their skin. The blubber insulates their body so they don’t lose body heat while swimming in icy waters.

Feather and fur also have low thermal conductivity and are good for keeping warm. They also trap air—another substance with low thermal conductivity—creating an insulating layer of air around the body. If the animal feels cold, goose bumps fluff up their feathers or fur, which traps more air to slow down heat loss. This is why down jackets are so cozy: Down traps air, and this air layer insulates us.

You can test these materials out for yourself: This experiment in Advances in Physiological Education uses bubble wrap and vegetable shortening to demonstrate how fat and air work as insulators. Show us how your experiment turned out. Tweet a photo and use the hashtag #ISpyPhysiology.

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.

Why Do You Gasp for Air on a Cold Winter’s Day?

Winter running - Young woman running outdoors on a cold winter d

Credit: Getty Images

I live in South Dakota where the winter days can be frigid and very dry. Many people, including me, have difficulty breathing while exercising in the winter because our airways temporarily narrow during exercise. This condition is called exercise-induced bronchoconstriction (EIB), formerly known as exercise-induced asthma, and it’s often triggered by working out in cold, dry air.

Scientists believe it’s the dryness of the air breathed in and the quality of the air, not the coldness, that cause the airways to narrow. The lungs have a number of defense mechanisms and reflexes to protect the small airspaces from dry air and particles in the air. The extensive network of airways moistens and warms inhaled air so that by the time the air arrives at the gas-exchange areas—where oxygen enters the blood and carbon dioxide leaves—it is humidified and the same temperature as the body. The airways are lined with mucus that helps catch inhaled particles through its stickiness. The airways also can constrict to prevent particles and dry air from getting farther into the lungs. Narrowing causes problems, however, because less air reaches the gas-exchange areas, preventing the body from getting enough oxygen.

How can you tell if you have EIB? You will experience one or more of the following symptoms, which last 10 to 15 minutes after you’ve finished exercising:

  • shortness of breath or wheezing,
  • decreased endurance,
  • tightness in the chest,
  • cough,
  • upset stomach and
  • sore throat

While 90 percent of people with asthma have EIB, not everyone with EIB has asthma. You’ll need to see an allergist to determine whether your symptoms are solely exercise-induced, are a reaction to irritants in the air or are indications you have asthma.

EIB doesn’t have to keep you from exercising in the winter. In fact, many elite cross-country skiers, world-class figure skaters and ice hockey players have EIB. Here are some suggestions from the American College of Allergy, Asthma and Immunology to relieve your symptoms:

  • Warm up with gentle exercises for 15 minutes before starting intense exercise.
  • Cover your mouth and nose with a scarf or face mask.
  • Try to breathe through your nose.

Medicine that widens the airways can also be prescribed to help prevent your symptoms and attacks. I try not to take a deep breath when I go outside on a cold South Dakota winter day. Then, I head out on a four-mile walk with my golden retriever.

Barb Goodman, PhD

Barb Goodman, PhD, is a  a professor of physiology at the University of South Dakota.