Exercise: good or bad for your immune system?

Philip J. Goscienski, M.D.

May 2007

Baby boomers belong to the post-penicillin generation. By the time they arrived most of the bacterial scourges that had afflicted humanity for hundreds of thousands of years were on the way to disappearing because of the discovery of penicillin and other antibiotics during the 1930s and 1940s. Earlier generations, going all the way back to the Stone Age, had to rely for survival on a healthy immune system. A wound from a spear or even a splinter could end in death from infection.

It is our immune system that enables us to survive the countless microorganisms that we encounter every hour of our lives. There are hundreds of thousands of species of germs that we have to deal with — bacteria, viruses, fungi and parasites — and the defense mechanisms that humans have acquired over the millennia are unimaginably complex.

Scientists are gradually unraveling the phenomenon of immunity but it's clear from several studies that persons who exercise regularly have fewer colds, and perhaps serious infections, than couch potatoes.

Until about 10,000 years ago Stone Agers lived just as any wild creature, with no shelter, plumbing, safe water or clean food. This constant exposure to the varied germs in their environment no doubt pushed their defense mechanisms to their limits. Vigorous physical activity is a factor. When a person runs, for example, there is a temporary surge in the release of white blood cells and circulating chemicals that fight infection. This is just what a hunter or warrior needed to ward off germs that might enter the body from wounds.

Protein is a key ingredient of all the factors that make up our immune system. Resistance exercise builds muscle, which consists almost entirely of protein. During epidemics of influenza the highest mortality occurs in the elderly. One reason that their immune systems are inadequate may be that they simply don't take in enough protein or they have small protein reserves because their muscles have wasted away from inactivity.

Moderate exercise improves immune function but very strenuous exercise, especially when prolonged, weakens it. Long distance runners frequently develop upper respiratory infections during the weeks following a race. The reason remains a mystery. Joggers and casual runners have nothing to worry about. It takes a high level of training to induce even this mild susceptibility to minor infections.

Regular exercise is one of the best preventive measures against type 2 diabetes and thus provides, indirectly, protection against infectious diseases. One of the complications of diabetes is a susceptibility to infection. The high blood sugar that is the hallmark of diabetes interferes with the activity of white blood cells. Diabetic patients have poor blood supply to the feet and poor nerve sensation. A minor skin injury that goes unnoticed allows infection to progress before the body's impaired defenses can react. This is sometimes the first step in gangrene that leads to amputation.

As type 2 diabetes climbs to unprecedented levels this is clearly one of the most important reasons for making exercise part of your daily routine.

Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at drphil@stoneagedoc.com.