Exercise-Induced Illness: The Open Window

Not too long ago a reader of this blog wrote in complaining that he suffered from periodic flu-like symptoms that tended to bedevil him after training hard or playing especially tough squash matches. He is in top shape, and was wondering why this would happen to him of all people and if there might be anything he could do about it.

That's a good question, and unfortunately there is no definitive answer.

There is no doubt that moderate exercise is good for you and, more specifically, your immune function. But exercising at a peak level, such as what one might do during a difficult hourlong squash match, can put the body under immunological stress. Elite athletes in many sports have long suspected that overtraining can lead to bouts of illness, particularly increased upper respiratory tract infections (URTI). Studies have found that these athletes are correct.

Indeed, epidemiologic studies have proven that URTI risk rises with heavy training (Nieman DC, et al. J Sports Med Phys Fit. 1990;30:316-328).

So what exactly is happening immunologically after intense exercise? Well, here comes some science....

There is a decrease in NK cell activity, which may heighten risk of viral transmission. NK cells are 'natural killer' cells that protect against infection.

Development of neutropenia (low blood neutrophil) or neutrophilia (high), depending upon the athlete. Neutrophils are an essential component of the body's innate immune system, and are involved in the phagocytosis of both bacterial and viral pathogens. (Phagocytosis means to encircle and destroy -- a good thing!)

Development of lymphopenia (low blood lymphocyte count), important since these white blood cells are integral to the development of immunity and should increase in number in response to an infection. Also decreasing is mitogen-induced lymphocyte proliferation, which is a way to gauge the function of T lymphocytes (called 'T' because they are dependent upon the thymus).

Increases in pro- and anti-inflammatory cytokines, which mediate cellular interactions. Types of cytokines include interleukin-6, -10, and interleukin-1 receptor antagonist.

Depression of serum immunoglobulin levels, including IgA and IgG, both commonly found in airway secretions.

And there are other changes, but we are not reading this to get an advanced degree in exercise immunology, so let's cut to the chase....

The fact is that most immunologists now believe that there is an 'open window' after intense exercise in which the athlete experiences some level of impaired immunity (which can last anywhere between 3 and 72 hours, depending on the immune measure) and during which both viruses and bacteria may achieve a foothold. Lack of sleep, unusual mental stress, malnutrition and recent weight loss may all decrease immune function further.

So why would my reader be bothered by exercise-induced illnesses while many other squash players of equal intensity not experience these problems? I suspect the answer lies in the difference between the innate immune system and the acquired immune system. The innate system, which as its name implies is the system we are born with, is greatly affected both by genetics as well as nutrition in early life. One's genetics may just not support a vigorous innate immune system. Likewise, poor nutrition as an infant and child may not have provided the needed micronutrients to build up one's innate system. My reader may keep getting tripped up by an innate system that is not as vigilant as it might have been, for want of better nutrition.

When the innate immune system fails, the acquired immune system kicks in. The term 'acquired' is used because this system relies on the immunological memory of specific infectious agents to which the body has been subjected. The acquired immune system relies on such cells as the B- and T-lymphocytes -- the very cells that are temporarily decreased following strenuous exercise.

OK, so what to do? In addition to the obvious -- eat right, get enough sleep, don't stress out too much -- is there anything one might take? Several micronutrients are very important for optimum enzyme function, including zinc, iron, copper, selenium, and vitamins A, B-6, C and E. Eating correctly, however, easily takes care of these nutritional needs, and studies testing if high-dose supplements of these vitamins are beneficial against exercise-induced illness have failed to show any definitive benefit. Other studies looking at plant sterols, N-acetylcysteine, butylated hydroxyanisole, and glutamine have also failed to show a definitive effect. The jury still seems out on newer immunonutrition supplements, including beta-glucan, curcumin, and quercetin, but I have my doubts about them as well.

And here I would stress caveat emptor -- buyer beware. There are a lot of nutrition and supplement companies out there, none of which have to answer to the FDA and thus can pretty much say just about anything about their product. The usual line is: "This product supports [body part] health." It's a load of crap -- this industry needs much better regulation, because people are wasting a lot of money on often useless supplements, and sometimes are ingesting these agents at toxic levels. Don't be a sucker!

The one nutritional intervention that HAS proved helpful for elite athletes is carbohydrates, usually ingested in the form of a sports drink (or flavored cookies and bars). Carbohydrates reduce perturbations in immune cell levels and lower inflammatory cytokines.

So for my reader I would suggest two things:

Carbohydrates, before, during and after intense activity. In addition, there are many specific approaches one can take that involve food (e.g., avoid refined carbs and saturated fats, etc.), so a consultation with an experienced exercise nutritionist would likely be money well spent.

Moderation of his most intense activities. If he is currently playing 4 tough matches a week, then he should try ratcheting back to 3, and using that extra day to work in the gym on core strength, without raising his heart rate too high.

My reader is an athlete in great condition, so cutting back is not what he wants to read, but he should consider this: 3 good matches played fit is better than 4 played sick.

For those interested, the following reference is a good overall review of this issue: Moreira A, et al. Does exercise increase the risk of upper respiratory tract infections? Br Med Bull. 2009;90:111-131.