Can exercise make you sick?
It’s no secret that regular physical activity is the key to good health. Being fit protects us from a slew of chronic conditions like heart disease, diabetes, and some cancers (source).
That’s pretty darn awesome. I’m all about adding healthy years to my life. But, at the ripe old age of 28, my own mortality is not normally at the forefront of my mind.
So when I think of health threats (besides my fertility issues), I think more along the lines of running injuries or infectious illnesses, like a cold or the flu.
Which leads me to my thought of the day: does endurance exercise help our immune system or hurt it?
I’m not a doctor, nor am I going to do a thorough literature search, so please understand these are just my thoughts based on a very limited amount of research. (Bad, bad health educator)
Now, I know moderate exercise boosts your immune system. People who exercise regularly, for 30 to 75 minutes at a time, get far fewer colds than those who don’t (source).
But apparently you can have too much of a good thing. Experts say that when you exercise for 90 minutes or longer without taking a break, the immune system starts to wear down and you become more susceptible to infections. This vulnerability can last anywhere from 3 hours to 3 days (source and source).
That’s insane to me. When I was triathlon training, I’d have 3 workouts per week (long run, long bike ride, brick) that would crack the 1.5 hour mark. Most marathoners have one or two training runs a week that last longer than 90 minutes. And if you’re training for an Ironman? Forget about it! You may have two training sessions a day that each last more than an hour and a half.
Have any of you noticed if you get sick more often during training? I personally haven’t experienced this much. I don’t get sick often. I’m more fatigued for a couple of days after a long run, so I take it easy. This likely helps my immunity; along with fueling properly, taking rest days, being a germ-o-phobe, and getting regular chiropractic care.
Hand sanitizer is my BFF.
Post-race is another story though. How many of you have gotten sick in the week after a big race? I always feel really worn down after racing. And I often catch a cold a few days later. I think it has something to do with the time spent on my feet and the intensity at which I push myself.
I have a theory that ultra-endurance exercise events, like an Ironman, wear down your immune system for much longer than 3 hours to 3 days.
At least in my case study experience. There’s this guy who doesn’t get sick. I’ve known him for 10.5 years and I’ve never seen him with more than a case of the sniffles. Then he did an Ironman in November. He caught a cold the week after and had a horrible bout of the flu on New Year’s. Mmmhmmm.
Of course this could be a complete coincidence. But I don’t think so. I’m just going to accept that Ironman racing is bad for your immune system, so I have an excuse never to do one 
What are your thoughts on exercise and sickness?
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January 8th, 2011 - 10:18
Great post! I’ve done 8 marathons and 2 ultras, and I’ve probably come down with a cold before 1/3 of them, around the time of my longest training run. I do believe that putting my body through hours of training at one time can suppress my immune system. That combined with not washing my hands enough and working in a sea of cubicles has made for a bad combo, and I’ve ended up getting sick.
I think though that with property nutrition, lots of hand washing, and avoiding super populated areas for a day or two, you can probably avoid catching a cold.
January 8th, 2011 - 10:28
Well, I am certainly no doctor or expert on this, but one time, I had a cold and I did a hot Brikham yoga class to “sweat it out.” I felt awful the entire class, but was complete fine the next day!
I think another thing to consider is all the germs at the gym. Yes, working out may be good for your immune system, but does it really matter when you go to the gym and touch all the nasty weights and stuff? Sounds like a wash to me.
January 8th, 2011 - 10:59
Whenever I feel myself about to get sick, I take it easy. I take a day off. I get more sleep. I sleep-in instead of getting up at 6am for the gym. I’ve been pretty lucky so far this year (well 2010) and I hope that continues this year!!! I hate being sick!
January 8th, 2011 - 11:10
i think you’re right on the money…but, i’ll take my chances. i’m pretty sure the long term benefits outweigh getting a little sick right now. at least that’s what i’m telling myself while its snowing buckets outside and i have a 15 miler to tackle tomorrow….
January 8th, 2011 - 11:52
I totally agree with your conclusions. I’m in the 30-70 minutes, 5 days a week exercise camp, and my immune system is bananas. I used to be obese and never exercise, and I was seriously sick all the time–constant colds and sinus infections and the flu at least once a year. Now I get sick maybe once a year, even though I’m constantly trapped on planes and shake tons of hands for my job. It’s awesome!
My unscientific study is that I exercise and never get sick, and I’m not a germophobe at all. My coworker who never exercises, but uses paper towels to touch pretty much ANY community space, is sick at least once a month.
January 8th, 2011 - 11:54
I think each individual is probably different. Also sleep patterns and nutrition probably weighs in pretty heavily. Extra stress plus poor nutrition plus over exerting yourself probably would equate to an increased chance of getting sick but as long as you’re taking care of yourself I’ve always noticed that I stay much more healthy the more I exercise.
January 8th, 2011 - 11:56
I think you are onto something for sure. Pushing yourself that hard has to have some sort of effect on your immune system. Like you, I definitely notice I am exhausted after a long run or race but I will just make sure to get lots of extra sleep (I always take a nap after my long runs!) and try and take it easy for a few days. Usually does the trick
January 8th, 2011 - 18:13
Such an interesting post! I tend to follow the camp that the more active you are, the less you get sick. But of course there is that fine line you mention of being too active…
I definitely think too much exercise (though, typically a good and beneficial thing) can wreak havoc on your immune system if you do too much in too little time. Balance is key! For everything!(Now I just need to keep trying my hardest to live by these words…ha!)
January 8th, 2011 - 18:31
Interesting topic, Jen! I have noticed that my body starts to feel sick and break down a little after I’ve been training hard and then finally start to let up. During marathon tapers I will get sick sometimes. No idea if there’s anything scientific to back that, but I think its interesting because a lot of people have different opinions on exercise’s effects on illness.
January 8th, 2011 - 20:47
I think you’re on to something with this intensity theory! I don’t get sick very often either, but I have gotten sick (nothing major just colds) after marathons. I’ve also found that I’m more likely to get sick during times when I’m running really high mileage. In the past, I’ve had problems with over-training which not only led to injury, but also left me feeling worn down and sick.
It’s definitely interesting to think about. Especially since everyone’s body is different. Maybe it could make your immune system more susceptible, but there must be things you can do to counter-act it. I mean, how do professional ultra marathoners run so much and not get sick?
January 8th, 2011 - 22:45
Knock on wood – I’ve been quite healthy lately. That said, my last bout with a cold was the week after my marathon. I know many others that experienced the same thing. I haven’t experienced it while training for long distances, but the race itself wore me down. My theory was that the adrenaline high that I was on masked my fatigue and I didn’t rest properly immediately following the race. I had such a rush, I thought I was totally fine! Wrong. After training runs, I also refuel and rest properly to allow myself to recover. This is such an interesting topic!
January 8th, 2011 - 23:31
hmmm i dont know. all we have is our experiences to draw from and ive never gotten sick or run down from races so i dont know. but it makes sense that your body would be wore out after a huge effort like a marathon or triathlon, etc.
January 9th, 2011 - 00:43
I get sick after almost every single 1/2 or full marathon. It’s pretty crazy. Occasionally a hard long run will bring me down as well. Not sure why. I think I’m extra prone to getting sick these days which is weird to me. I used to be so immune to everything. It seems like now my stress levels are so much higher that the running on top of it just sends me over the edge.
January 9th, 2011 - 11:57
My boyfriend was a professional cyclist for 3 years and often talks about how he would get sick during certain times of his training. He also slept in an altitude tent for a year to help the regeneration of muscles. But I definitely think there is something to be looked into for immune response after an intensive level of physical activity. If your body is working to rebuild muscle tissues then in a number of ways it make sense that your immune system wouldnt be able to overcome a cold.
January 9th, 2011 - 15:37
The week before a big event I’ve started taking Airborne, which seems to help me stay healthy before and after (or it may all be psychological).
My concern has always been exercising with a cough. I have asthma and allergies and sometimes get “coughy,” but am not sick (or as a teacher sometimes I do pick up the kids’ germy coughs). Some of the research I have found has said working out is okay if the sickness is above the shoulders but to rest if below. Thoughts anyone?
January 10th, 2011 - 13:39
I never got sick during my training for my first half, which I ran on Saturday.
However, I woke up this morning with a scratchy throat. :/ Something to think about.
I know that I pushed myself a LOT during my race. While I was training, I would stop sometimes to catch my breath and stretch. However, the only time I stopped during my race on Saturday was to use the rest room at mile 1.4 (ugghhhh) and I briskly walked through water stations. But then again, never ONCE during my race did I WANT to stop.
January 10th, 2011 - 16:56
This was very interesting. For me personally, I think that I have a tendcy to get sick when I let myself get sleep deprived. I think that when my training picks up, my hours spent sleeping also needs to go up. I was reading an article in which Ryan Hall says something similar. He says as part of his training plan he schedules naps during the middle of the day!
January 10th, 2011 - 17:03
Each individual is probably different.
I’ve always noticed that I stay much more healthy the more I exercise. I think too much exercise can wreak havoc on your immune system if you do too much in too little time.
Balance is key!.
January 10th, 2011 - 18:00
So after my first marathon I got a UTI and after my second I got a really bad cold. I definitely buy into the weakened immune system theory. Endurance events put sooo much stress on your body and I think it’s so easy for you to pick up germs when your body is fighting so hard to repair itself after the trauma of the race.
January 11th, 2011 - 12:33
My unresearched opinion is that lots of exercise without proper rest (time off and sleep) can result in a weakened immune system.
Exercise makes me feel good. So even if it did mean a few more colds, it would be worth it to me.