Defend Your Immune System

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If you were living in a cave during prehistoric times, or perhaps in a medieval hut or a trench during World War I, what would be your greatest fear? Other than attacks from predators or warring humans, bacterial infection in all its various faces would fill you with the most dread. Will that cut on my foot fester? Will this water make me sick? What if these rats actually do carry the plague?

Because the menu of dreaded diseases has changed over time, those of us who lie awake in the middle of the night these days might be worrying, not about gangrene, but about the equally frightening bogeymen of cancer, influenza, SARS, HIV or West Nile virus.

What hasn’t changed since the dawn of time is our greatest defender against all these foes: our immune system. When functioning properly, it kills bacteria, viruses, fungi and parasites. It hunts for and destroys cancerous cells or those infected with a virus. To do this work, our amazing immune system produces several types of cells (phagocytes, T-lymphocytes and B-lymphocytes), antibodies and chemicals — all without assistance from us. However, several factors under our control — diet, sleep, exercise, reducing stress levels and choosing natural supplements — can assist the immune system’s performance.

The Stress Link

Whether physical or psychological, stress raises the level of an adrenal hormone called cortisol. Cortisol plays an important function in regulating blood sugar, energy production, inflammation and the immune system. But too much cortisol over the long run can wreak havoc on the immune system and other bodily systems. A study published in Psychosomatic Medicine in 2004 found that people who felt overwhelmed and otherwise psychologically stressed actually produced fewer antibodies in response to an influenza vaccine.

Fortunately, we can modify some of the things — exercise, sleep, smoking, diet — that add to our stress load. For instance, people who exercise regularly are less prone to developing infections and cancer. Strangely, some studies show that exercise enhances immune function, while others suggest it undermines such function.

I asked Roy Shephard, M.D., Ph.D., professor emeritus of applied physiology at the University of Toronto and author of Physical Activity, Training and the Immune Response (Cooper Publications, 1997), to clarify the issue. He answered, “There is some evidence that reasonable amounts of training enhance immune function, but extreme training [which decreases the testosterone/cortisol ratio] depresses both NK cell function and the secretion of immunoglobulins.” (NK, or natural killer, cells destroy other cells that have become cancerous or infected with viruses; immunoglobulin is another word for antibody.) According to Shephard, these immune factors decrease in the blood because exercise stimulates their migration into the tissues.

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