High mileage training lowers the immune system, so should all runners cut down their training?

I was doing 50/wk until I got sick in mid-February (which I am now convinced was covid19 based on symptoms and virulence-more than half my friends and cohorts had it). Now 20-25 4 days/week, with lots of drills, sprints short hills, lifting and cross-training. Today I will do my first long run since the illness, about 12 miles. Feel great, not going to push hard until weather warms up considerably and I can get lots of sun and vitamin D3.

Incorrect. High mileage training slightly suprresses the immune system in people who are not used to it. Don't make huge mileage jumps or overtrain and there is nothing to worry about.

The dynamics is important, not the absolute mileage.

When you up your mileage and feel awful the following day, yes. Once you get used to the mileage, then it's the new normal. In fact, I think for me the immune system is generally stronger now after several years of higher mileage; based on on milder symptoms of cold/flu, or maybe even (untested) Covid-19.

If you prepare for marathon and taper perfectly, your immune system is the strongest just before the start. It's the weakest at the finish (or maybe even, at 20 miles).

Glendower wrote:

Running over 40 miles per week, lowers testosterone and makes you more vulnerable to infection as it weakens the immune system, this is an established fact. So in light of this and the latest virus outbreak I think everyone should lower their mileage down. Is anyone changing their training to account for this? Maybe good timing to switch to pre-hab training, more focus on lifting weights/stretching routines and lowering the mileage down to 30mpw.

Not an established fact. Long endurance runs only temporarily decrease lymphocytes in circulation because they situate themselves in your bone areas to trigger more white blood cell production, and also accumulate around your lungs, to help your lungs deal with bad stuff you breathed in during the run. Within 24 hours of a marathon, your lymphocytes are back to normal appearances. Long moderate endurance runs move your lymph along, distributing lymphocytes better. So long runs make you better prepared to fight off a virus, not less.

I gleaned this from a NY Times article about a review paper centered in Bath, UK. I couldn't find a way to link it.

Seattle Flu wrote:

I was doing 50/wk until I got sick in mid-February (which I am now convinced was covid19 based on symptoms and virulence-more than half my friends and cohorts had it). Now 20-25 4 days/week, with lots of drills, sprints short hills, lifting and cross-training. Today I will do my first long run since the illness, about 12 miles. Feel great, not going to push hard until weather warms up considerably and I can get lots of sun and vitamin D3.

vitamin D1 > vitamin D3

Wrong. Being fit dramatically boosts the immune system. Proven fact.

The interview just above mentions this article, which is open access:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5911985/

Here's the relevant passage in the interview:

Zhu: What about intensity? It seems that most studies and reviews say that the intensity of the exercises should be kept moderate. However, Campbell and Turner have recently challenged this belief and claimed that there is no harmful effect on immune function even when a vigorous bout of exercise intervention is employed. What is your view on the appropriate intensity of exercise for improving immune function?

Woods:The report from Campbell and Turner focuses on highly fit individuals who compete in, and are accustomed to, long endurance, high-intensity events. While I believe there is merit in the evidence they provide to refute the conclusions for that population, studies where sedentary people are forced to exercise at high intensities for prolonged periods might paint a different picture.

So intense workouts may be okay if you're fit, but may not be a good idea if you're sedentary.

my 2c wrote:

So intense workouts may be okay if you're fit, but may not be a good idea if you're sedentary.

Fair enough. But it's not an oversight that this wasn't considered, because it's kind of a dumb question that no one really cares about the answer to, and it's far from the focus of research on actual athletes. But it would be a good study for The Journal of Modern Sedentariness!

Relevant to people who run regularly, say who were in the middle of a marathon buildup before everything got cancelled, the argument from Campbell and Turner is that all of the previous arguments and evidence assuming a weakened immune system related to intense or long aerobic exercise are, as they say, spurious.

It all depends on a person's training. Everyone should run according to their well-being. You should not strain your body to the limit. Only sports professionals can do that, and they take significant risks. But if you intend to pump up your sports skills, I suggest taking care of your health. Various supplements that support your immune system and improve the function of internal organs can help you in this. One such supplement is medicinal mushrooms. You don't have to worry because many of them have been independently lab tested. For starters, I suggest you try lion's mane mushroom https://www.inneratlas.com.au/products/lions-mane.

Most people’s immune systems are over active anyway.

Some suppression will do them good.

It depends on how your body is acquainted with the mileage.

Your immune system can be affected if you never run and you suddenly run 10 miles per week.

Imagine that ultra runners would be always sick.

Glendower wrote:

Running over 40 miles per week, lowers testosterone and makes you more vulnerable to infection as it weakens the immune system, this is an established fact. So in light of this and the latest virus outbreak I think everyone should lower their mileage down. Is anyone changing their training to account for this? Maybe good timing to switch to pre-hab training, more focus on lifting weights/stretching routines and lowering the mileage down to 30mpw.

Ahhhh….40mpw is low mileage.

flyingfacefk wrote:

Wrong. Being fit dramatically boosts the immune system. Proven fact.

Exactly

My obese relatives are always sick. Four of them got covid. In contrast my wife and I exercise a lot and rarely get sick. What’s important is eating nutrient rich foods, washing your hands, and getting enough sleep.

Now if you’re running 100 miles a week and not getting enough rest then yeah your immune system will suffer.

Tigbo wrote:

[quote]flyingfacefk wrote:

Now if you’re running 100 miles a week and not getting enough rest then yeah your immune system will suffer.

My guess is that running 100 miles per week itself, isn't enough to weaken your immune system enough to put one at significant risk. After all, are pro-runners a group you constantly hear about getting sick, dying of COVID or being hospitalized frequently for infections?

No.

If, on the other hand, you run 100 miles per week and it's more than you're ready for, your nutrition is poor, you're not resting enough and haven't built up to that level, then sure, it will take it's toll.

Give me the choice of having the immune system of a runner who runs 100 miles per week, versus the immune system of the average American, I'll take the 100 mpw immune system, every time.

Proper nutrition and sleep can enable the body to train at a high level while keeping the immune system strong. I train for +2 hours a day as a runner and XC skiier. The last time I got sick was 2 years ago, at a time which I was not getting enough sleep and eating enough fruits and vegetables. However if I do those things, I find that I can train at a very high and intensity without getting sick. Also as the other posters stated, a high training volume weakens the immune system much more in a person unaccustomed to the workload than in a person who already engages in this type of training.