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Exercise boosts your immune system — up to a point. A neat new paper in Medicine & Science in Sports & Exercise digs a little deeper into this complicated relationship between exercise and immune function. Specifically, it looks into the response of neutrophils:
When infection occurs, neutrophils rapidly migrate to the infection site (chemotaxis) and ingest the pathogens (phagocytosis).
So how does exercise affect these neutrophils? Well, that depends on what kind of exercise you do. For regular, moderate exercise (“CME,” or “chronic moderate exercise,” consisting of 30 minutes of moderate cycling daily for two months), here are the results:
“DT” is “detraining.” So you can clearly see that regular, moderate exercise boosts the ability of the neutrophils to get to infection sites quickly (chemotaxis) and attack the bad guys (phagocytosis). And in fact, the neutrophils are still ultra-alert for a couple of months after you stop training. In addition, the researchers found that regular exercise extended the life of the neutrophils.
On the other hand, the effects of “acute severe exercise” (an incremental test to exhaustion) had more mixed results. Chemotaxis was enhanced, but phagocytosis wasn’t, and the lifespan of the neutrophils was shortened — not so good for immune function.
So is this a surprise? Not really — it’s been clear for a long time that exercise has a J-shaped influence on immune function. Some is good, more is better, but beyond a certain point, too much is bad. Run a marathon, you’ll have a slightly elevated risk of catching a cold (or at least suffering from some sort of respiratory symptoms) afterward. But studies like this are needed to understand what exactly is happening in the body, so that eventually we’ll have a better idea of exactly where the curve in the J starts — and possibly figure out some ways to extend the sweet spot of the curve.
The impact of endurance training on both the immune system and the levels of hematocrit interests me greatly, but it’s hard to find much information on it. In particular, the question of whether endurance training results in hemodilution and in turn impacts on routine blood tests is one that I’d love to see addressed in lay terms. My instinct is that there is a gap between what physicians know about this and what exercise physiologists know about it. Thanks for maintaining your wonderfully informative site.
So, here’s a very interesting angle on this, I think:
Bear in mind that this “boost” to immune function isn’t necessarily a good thing! As a pain guy, what I see here is actually a mechanism for slower healing and greater pain chronicity as a consequence of exercise. I know that sounds really counterintuitive, but bear with me …
We know that neutrophils also, unfortunately, do their painful thing in response to aseptic (internal) trauma when there is no possibility of pathogens. They go nuts anyway, and attack — this is so cool/bad — exposed mitochondria — because mitochondria are technically, biologically “foreign,” a legacy of evolution and symbiosis. And this inappropriate immune response is a likely mechanism in overuse injuries, chronic pain, and a reason why it can take so long to fully recover from something like a sprained ankle. For details on this, see my article:
“Why Does Pain Hurt So Much? How an evolutionary wrong turn led to a biological glitch that condemned the animal kingdom — you included — to much louder, longer pain.”
So you can see the problem … if neutrophils routinely do this unnecessary, painful thing they aren’t supposed to do … and this evidence shows that neutrophil activity is actually enhanced in folks who are exercising … it could actually constitute a pretty interesting explanation for why so many amateur athletes are prone to a long list of common persistent injuries … which in turn is also a very common limiting factor in performance (a conversation I just had with some folks on my Facebook page). 😉
Heck of a gotcha!
@Paul Ingraham that is a great point. Molecular/cellular studies are obviously important, but because what goes on is so complciated and intricate, they need to be complimented with practical stuff(i.e. sure, look at neutrophils…but in conjunction with the frequency and duration of upper respiratory tract infections in the same population). Otherwise we just get into intellectual arguments that can go both ways.
I see the same type of thing happen over moelcular studies showing the impact of chiropractic manipulation on immune function (like this one: http://www.doaj.org/doaj?func=abstract&id=271227).
@Sean
“sure, look at neutrophils…but in conjunction with the frequency and duration of upper respiratory tract infections in the same population”
Just speculating, but could the mechanism Paul Inghraham describes also be responsible for the elevated level of URTI in runners, that, according to a recent post on this blog, does not seem to be linked to actual infection?