Why Do Colds Hit Asthmatics Harder Than Non-Asthmatics?
Respiratory viruses affect all of us. They enact an immune response that causes airway inflammation, and this inflammation causes cold symptoms. If you have asthma, this response may hit you harder than it does for the non-asthmatic population, potentially bringing out cold-induced asthma symptoms. How does this happen? Here’s what to know.
It begins with the immune system
Viruses are considered microscopic living organisms. They are smaller than bacteria. They cannot replicate on their own. To replicate, they must infect a cell. Respiratory viruses are partial to respiratory cells. They are easily inhaled and bind with airway cells. They infiltrate the cell, take over cellular structures, turning that cell into a virus-making factory.
Virus after virus after virus is churned out inside the cell. This goes on until the cell cannot hold any more viruses, and it explodes. This releases tens of thousands of tiny viruses to bind with other airway cells.
Immune cells also respond to this. They recognize the viruses as harmful. They, in turn, release tens of thousands of their own chemicals. These chemicals are pro-inflammatory chemicals that cause airway inflammation. This inflammation causes the production of sticky mucus to trap and kill the viruses. But, it’s also this inflammation that causes your cold symptoms.
So, if you do not have asthma, you just have cold symptoms. You can wait it out or you can treat symptoms. In a few days to a week, you are back to normal and your life goes on as usual.
Now, add in asthma to this response
Asthma is an abnormal immune response. Your immune system abnormally responds to otherwise harmless substances in the air. Or, it may respond to triggers inside your body, such as sex hormones or reflux. In either case, the immune system abnormally releases lots of pro-inflammatory chemicals. Many of these chemicals are the same chemicals your immune system releases in response to harmful pathogens like viruses and bacteria.
Over time, this airway inflammation becomes chronic. This means that these inflammatory chemicals may always be present to some degree. The presence of these chemicals makes asthmatic airways hypersensitive to asthma triggers. Another term for hypersensitive is "twitchy." It means airways are easily irritated by certain triggers. And, respiratory viruses are the most common asthma trigger. Respiratory viruses cause an immune response where pro-inflammatory chemicals are released. This causes your typical cold symptoms.
Theories on respiratory viruses causing cold-induced asthma symptoms
There are three theories that attempt to explain how respiratory viruses may cause cold-induced asthma symptoms:
- The immune response may easily work it's way to your lower airway; or
- It may drip down by means of nasal drainage; or
- Upper airway inflammation may be transferred to the lower airways by a neurotransmitter called acetylcholine. When this causes asthma symptoms it's called "reflex bronchospasm."
Complex? Indeed it is. And they do seem quite credible to this author. In any case, this can irritate your already inflamed airways to induce asthma symptoms.
One final theory
One theory I want to add here. The Rhinovirus is the most likely virus to cause respiratory infections in asthmatics. One study showed the Rhinovirus was 50% more likely to invade asthmatic airway cells compared with a control group (of probably non-asthmatics). So, this makes asthmatics more susceptible to respiratory infections.1,2
Asthmatics may have a diminished supply of a protein called interferon-beta. This makes it so virus-infected cells live longer in asthmatics than non-asthmatics. So, this means asthmatic cells are more likely to give viruses time to spread before the immune system can destroy these infected cells.1,2
This fourth theory is also neat in that it gives us a potential future treatment option for virus-induced asthma. The treatment would be type I interferons. So, this is something we can discuss further as researchers continue their research in this area.1,2
Beware of cold-induced asthma symptoms
Voila! You have a cold worse than others around you. Not only do you have to treat the cold, but you also have to treat the asthma component. This can sometimes be tricky to do, depending on how severe your cold-induced asthma symptoms are.
Bacteria affect cells differently than viruses do. Unlike viruses, bacteria can survive on their own. Still, respiratory viruses are the most common cause of colds. Studies indicate that viruses are responsible for around 85% of all asthma episodes. I will discuss the impact of bacteria on asthma in a future post. Still, I would imagine respiratory bacterial infections would also impact asthmatics worse than non-asthmatics.
You may also be interested in "Respiratory Viruses: The Most Common Asthma Trigger." Another article worth reading is "How Do Respiratory Viruses Trigger Asthma?"
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