Why The Immune System Gets Weaker When You Are Cold?

[Carl Fredrik Ahl]

Hi,

I wonder why you are more prone to get sick (get colds) when you are cold. How does the immune system get weaker?

[iNow]

I'll defer to a biologist here, but my understanding is that the bigger issue is people tend to huddle closer together when it's cold. We spend far more time indoors and in contact when it's cold than we do when it's warm and we're outdoors and farther apart from other humans.

There may be an effect from the body needing to burn calories to stay warm and reallocate energy from strong immune response instead to maintaining a baseline body temperature, but last I heard that is not a very powerful affect is is more of a myth.

Note: We could surely google this to confirm, and I'm not a biologist so concede in advance the above may be mistaken. I look forward to being corrected if that's the case.

[Prometheus]

I used to ask this question when i was a nurse and got all kinds of answers. Viruses prefer the colder temperatures in noses during winter; immune systems weaken during winter months as part of annual biorhythms; people seal themselves off from the outside world more to stay warm (similar to the huddle together one). Some mix of all the above. I never did find a definitive answer.

[Phi for All]

We don't get enough Vitamin D when we can't get outside often (as with colder weather), and that can lead to complications. Also, it's sort of a design flaw that when your nose is stuffy from a cold, you breathe through your mouth, which bypasses your nasal filtering system and allows more viruses and bacteria in. 

[CharonY]

We are talking about different measures here. Weaker immune system is a mechanistically different from increased infection rate. The latter is also dependent on a lot of different external factors. On the tissue level coldness can affect vasoconstriction, another element of respiratory infections. One aspect that is also unrelated to the immune system is dryness in the winter time, which affects mucosal surfaces.

When we talk about the immune system proper, we have to look at factors influencing things on the  (sub)-cellular level. And here things get quite complicated to a degree that I do not expect MDs to have a deep knowledge about.

For starters, all kinds of stressors have the potential to affect cytokine expression and inflammatory signaling in general. Also if locally temperatures are lowered, immune cell responses are significantly altered, However, that link is mostly derived by in vitro experiments and it is not clear how applicable it is to animals. Additional stress such as exercising in cold does effect the lymphatic system, but it is not clear whether the observed changes are actually immune mechanism in any measurable way. In short, we know things change at lower temperature, especially when cold air is inhaled or the body is also stressed with other factors. However, we do have a bit of a knowledge gap in translating that molecular change into actual health outcome. As usual, biology is multifactorial and it is quite difficult to make easy explanations based on what we know.

[PhilGeis]

What are the data that support immunocompromise due to specific temperature exppsures?

[mistermack]

On 8/29/2019 at 10:34 AM, Carl Fredrik Ahl said:

Hi,

I wonder why you are more prone to get sick (get colds) when you are cold. How does the immune system get weaker?

I can't add any hard facts, I've heard plenty of anecdotes, but they don't constitute hard evidence. 

One thing to remember though, is that humans are not evolved for cold climates. We evolved fairly close to the equator, and only spread around the globe after we learned to keep warm artificially with clothing etc. Modern humans probably made it out of Africa about 75,000 years ago give or take 25,000. And they were already adept at making clothing and shelter and fires. 

We simply haven't got the long period of evolution of surviving chills that our pet dogs have, for example. We are evolved for coping with a quick chill of a downpour, followed by steamy heat. Not prolonged cold. 

When we get cold, our body automatically begins shutting down non-essential parts. We let the temperature of our extremities drop, and keep the heat as deep inside as possible, to lose heat at a slower rate, and protect the vital organs. It could be that the immune system gets less priority for resources, when you get chilled, in order to direct the available energy towards keeping your vitals warm. 

By devising warm clothing, and effective shelter, we prevented the evolution of greater cold tolerance. Instead of dying, we've been adapting using artifice, and that's not good for evolution.

Edited November 21, 2019 by mistermack

[Strange]

35 minutes ago, mistermack said:

One thing to remember though, is that humans are not evolved for cold climates.

Which is why Inuits look exactly the same, and have the same physiology, as people from Africa. 

[John Cuthber]

1 hour ago, mistermack said:

We simply haven't got the long period of evolution of surviving chills that our pet dogs have, 

We have been around for longer than pet dogs.It kind of follows from the definition of "pet".

 

And "Where the domestication of the dog took place remains debated, however literature reviews of the evidence find that the most plausible proposals are Central Asia, East Asia, and Western Europe. "

From
https://en.wikipedia.org/wiki/Origin_of_the_domestic_dog
 

So, that's plainly after we left Africa.

[mistermack]

So, in your view, the evolution of dogs started with domestication? I think you'll find that it goes back millions of years before that. 

And Strange contrasting Africans with Inuit is ludicrous. The real contrast is between the Inuit, sleeping inside an efficient shelter, lying on a bed of animal pelts, covered in a thick layer of animal pelts, and his husky, sleeping outside in minus thirty, wearing nothing. 

[Strange]

56 minutes ago, mistermack said:

So, in your view, the evolution of dogs started with domestication?

No one said that.

56 minutes ago, mistermack said:

And Strange contrasting Africans with Inuit is ludicrous.

Really? You can't see any differences? Or you think the differences aren't due to evolution?

 

[CharonY]

On 11/21/2019 at 8:10 AM, PhilGeis said:

What are the data that support immunocompromise due to specific temperature exppsures?

I think that is an excellent point and as per my above post, to my knowledge the connection is unclear and may very well be unspecific (assuming it exists in the first place outside of in vitro experiments). As such I suggest that the thread goes back to discussing the fundamentals of the question asked in OP rather than introducing highly speculative evolutionary anecdotes. The only things I would like to add is that it is obviously that adaptations in humans precede the time before they were considered a new species (or in other words, we need to look at least at hominins as a whole)  and at the same time minor adaptation can occur in a relatively short amount of time (such as Strange pointed out). Examples include differences in shivering responses or vasoconstriction in different populations. In addition, one hypothesis regarding human evolution is that they evolved in a time when climate patterns were unstable with decreasing temperatures and humidity. The variability selection hypothesis (championed by Potts) then states that hominin evolution is not an adaptation to a particular set of environmental parameters, but instead is shaped by the instability itself. That would explain the variability of the human species (and implicitly it also shows that evolutionary narratives of human behaviour are often"just-so"  narratives as the latter typically rely on a defined set of selective pressures to have any kind of predictive powers).

Edit: I realized that I may have veered off to far from my original point, but the response is more meant to indicate that grand evolutionary narratives are unlikely able to address OP and we would rather need to focus on direct evidence linking temperature to immune responses, if we can find them.

[John Cuthber]

On 11/21/2019 at 9:46 PM, mistermack said:

So, in your view, the evolution of dogs started with domestication? I think you'll find that it goes back millions of years before that. 

Which variation of stupid are you being?
The evolution of dogs and people started at the same time since (like all mammals) we have a common ancestor. That invalidates your claim that our pet dogs have had longer to evolve than we have.

And you said "pet dogs" and they only became pet dogs after we started petting them. That invalidates your claim that our pet dogs have had longer to evolve than we have.

[mistermack]

19 minutes ago, John Cuthber said:

Which variation of stupid are you being?
The evolution of dogs and people started at the same time since (like all mammals) we have a common ancestor. That invalidates your claim that our pet dogs have had longer to evolve than we have.

And you said "pet dogs" and they only became pet dogs after we started petting them. That invalidates your claim that our pet dogs have had longer to evolve than we have.

I'm afraid it's you that's being dense.

I was clearly pointing out how long we have been evolving mechanisms of coping with the cold. And I clearly referenced the out of Africa figure of 75,000 years. Dogs evolved from wolves, and they have been coping with colder temperatures for millions of years, in contrast to humans. It's simple stuff, all there in my post. You seem to have lost track of what the thread is about.