THE CLINIC:How Does Distance Affect My Immune System?

QUESTION:

I have been told that running distance for up to 90 minutes can enhance your immune system, but any more than that begins to compromise it. I run about four days a week and have been doing so for the past six years. I’m 56 years old, and average 20 to 25 miles per week. I always include one 9-mile run each week, which puts me in the 90-minute range for a single run, and so I wonder whether this rule of thumb is accurate. I’m thinking of trying a marathon, which would involve increased training. Do I run the risk of impairing my immune system if I take on any longer runs or more mileage?

Sylvia Kovach

Edgewater Park, NY

ANSWER:

It’s well documented that intense endurance exercise can temporarily impair the immune system. Several studies have shown that during the two weeks following a hard, long-distance race of 10K distance and up, 50 to 70% of runners may experience symptoms of upper respiratory tract infections (URTI). And, it seems that those who race faster and train longer and harder are more susceptible.

The literature also shows that regular, moderate exercise at 60 to 80% of aerobic capacity improves immune function. It also does not increase the risk of URTI, and when subjects exercised moderately 45 minutes per session 4 or more days per week there was some evidence that it even reduced the risk. 

I would describe your program as moderate, although you do one 9-mile run per week. If you are concerned about enhancing your immune system during training, you might try taking a replacement drink that provides carbohydrate and perhaps a little protein before, during, and after your workouts, particularly the longer ones. I am not aware of the 90-minute rule of thumb, and suspect it might be spurious.

Tom LaFontaine, PhD, FACSM

Columbia, MO

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(RUNNING & FITNEWS^® November / December 2011 • Volume 29, Number 6)