Step 97: Walk Away From Infection

As with resistance to cancer, fitness also provides protection against infections. The ability to ward off the threats posed by the sea of bacteria and viruses in which we live is dependent on elaborate and still not totally understood mechanisms. In the last 10 years we have discovered dozens of body chemicals that protect us, and physical exercise has been shown to provide higher levels of many of these defense compounds. Fit people get colds less often. The Centers for Disease Control in Atlanta found that those people who jogged 25 miles a week had one or two respiratory infections per year compared to the general index population of three per year.

Find the Right Balance

Of course, it was also found that 13 percent of the people who ran in the Boston Marathon in 1987 came down with flu or colds within a week of the race, compared with only 2 percent of the spectators. British Olympic gold medalist Sebastian Coe failed to qualify for the 1988 games because of a debilitating cold. Why? Overtraining not only fails to increase resistance to infection, but it also probably lowers it.

How does exercise increase immunity? The link is not fully established, but we do know that physical exercise is accompanied by an outpouring of adrenalin, the compound that makes the heart pump faster and produces sweating and metabolic adaptations such as high blood sugar. It also makes the body temperature go up, such as during infection. Adrenalin causes the spleen to release immune substances and the number of infection-fighting white blood cells to go up as well. It is also possible that adrenalin provides benefit to allergy sufferers as well. Many allergy medications have as their primary ingredient adrenalin or a related compound.

When exercise is extreme, however, the stress state results. Stress is accompanied by higher levels of cortisone. Cortisone, unlike adrenalin, produces a decreased resistance to infection and is potentially the component that puts competitors straining at the edge of their abilities at risk.

Regular, Sustained Exercise Is Key

A clear marker of older people is a reduced immune response. But we must ask again whether the decreased response is due to aging or inactivity. We haven't recruited enough 100-year-old athletes to answer this question definitively, but it seems likely that the reason older people seem prone to infection is that they are often frail -- not only in bone and muscle, but in antibody response as well. The logical proposition, then, is to offset the supposed decline in resistance to infection as we age. You need to retain fitness over the lifetime, not as a weekend warrior who puts yourself constantly at risk by overdoing and putting a stress on your body systems, but with a planned, regular exercise program in which all body systems participate in a meaningful way.

This does not mean that you should continue to exercise when you are really sick with an infection. If you have fever or general symptoms such as muscle aches or headaches, you should lie low for a few days. But don't let a runny nose alone interrupt your active lifestyle.