Scientists have finally discovered why people get colds and flu in the winter


Scientists have finally discovered why people get colds and flu in the winter.

There's a chill in the air, and you all know what that means — it's time for cold and flu season, when everyone you know suddenly seems to be sneezing, sniffling, or worse. It's as if those pesky cold and flu germs are around with the first about of winter weather.

However, germs are present year-round – think of that last cold you had in the summer. So why do people get more colds, flu, and COVID-19 when it's cold outside?

In what they call a 'breakthrough,' scientists have revealed the biological reason we get more respiratory illnesses in the winter - that cold air destroys the immune response in the nose.

"This is the first time we have a biological and molecular explanation for a single factor of our innate immune response that appears to be limited by cold temperatures," said Dr. Zara Patel, MD, a rhinologist and professor of otolaryngology and head and neck surgery at Stanford University. 

Lowering the temperature inside the nose by as much as 9 degrees F (5 degrees C) kills nearly 50% of the billions of beneficial cells that fight bacteria and viruses in the nostrils, according to a 2022 study published in The Journal of Science: allergy and clinical immunology.

"Cold air is associated with increased viral infections because you've lost half your immunity because of that slight drop in temperature," said study author Dr. Benjamin Blair, director of otolaryngology research at UMass Eye and Ear and an associate professor at Harvard Medical School in Boston.

"It is important to remember that these are in vitro studies, which means that although human tissue is used in the laboratory to study this immune response, it is not a study conducted inside someone's actual nose," Patel said in an email. "The results of in vitro studies are often confirmed in vivo, but not always."

Hornets' nest

To understand why this happens, Bleier, his team, and co-author Mansoor Ameeji, who chairs the Department of Pharmaceutical Sciences at Northeastern University in Boston, went on a scientific hunt.

A respiratory virus or bacteria invades the nose, the main entry point into the body. The team immediately discovered that the front part of the nose detects the germ before the back of the nose realizes the intruder's presence.

At this point, the cells lining the nose immediately begin creating billions of simple copies of themselves called extracellular vesicles, or EVs.

"Electric cells cannot divide like cells, but they are like small versions of cells specifically designed to eliminate these viruses," Bleier said. "EVs act as decoys, so when you inhale a virus, the virus sticks to these decoys instead of sticking to the cells."

These tiny cells are then expelled into the nasal mucus (yes, mucus), where they stop invading germs before they can reach their destinations and reproduce.

"This is one, if not the only part of the immune system that leaves your body to fight bacteria and viruses before they enter your body," Bleier said.

Bleier said that once they are formed and spread in nasal secretions, billions of EVs begin to swarm invading germs.

"It's like you kicked a hornet's nest. What happens? You might see some hornets flying around, but when you kick them, they fly out of the nest to attack before that animal can get into it." "This is how the body clears out these inhaled viruses so they can't enter the cell in the first place.

Significant increase in immune strength

The study found that when the nose is attacked, the production of extracellular vesicles increases by 160%. There were additional differences: The electric cells had many more receptors on their surface than the original cells, enhancing the ability of billions of extracellular vesicles in the nose to stop viruses.

"Just imagine the receptors as little arms sticking out, trying to grab the viral particles as you breathe them in," Bleier said. "We found that each vesicle has up to 20 times as many receptors on the surface, making it very sticky."

Cells in the body also contain a viral killer called micro RNA, which attacks invading germs. However, the study found that EVs in the Nose contain 13 times more precise RNA sequences than normal cells.

So, the nose comes into battle armed with some extra superpowers. But what happens to those advantages when cold weather comes?

To find out, Blair and his team exposed four study participants to temperatures of up to 40 degrees Fahrenheit (4.4 degrees Celsius) for 15 minutes and then measured the conditions inside their nasal cavities.

"We found that when you are exposed to cold air, the temperature in your nose can drop by up to 9 degrees Fahrenheit. This is enough to eliminate all three immune advantages that the nose has," Blair said.

Bleier said that a little bit of cold at the tip of the nose was enough to knock roughly 42% of the extracellular vesicles out of the fray.

"Similarly, you have roughly half the amount of lethal small RNA within each vesicle, and you can have up to a 70% reduction in the number of receptors in each vesicle, making it much less sticky," he said.

How does this affect your ability to fight colds, flu, and COVID-19? Blair said he reduces the ability to Help your immune system fight respiratory infections by half.

As it turns out, the pandemic has given us exactly what we need to help fight the cold air and keep our immunity high, Bleier said.

One expert says that wearing a mask can protect you from cold air, which can reduce your immunity.

"Not only do masks protect you from direct inhalation of viruses, but they are also like wearing a jacket over your nose," he said.

"The warmer you can keep the environment inside the nose, the better the innate immune defense mechanism will be able to work," Patel agrees. Another reason to wear masks!

In the future, Blair expects to see development in topical nasal medications based on this scientific discovery. These new pharmaceuticals, he added, "will essentially trick the nose into thinking it has just seen a virus."

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