Allostatic Load Scenario 4: Too Little Is as Bad as Too Much

by Bruce S. McEwen

January, 2006

Stress is just one of among a host of factors that contribute to what we call “allostatic load,” says Bruce McEwen, Ph.D., professor of neuroendocrinology at the Rockefeller University. Dr. McEwen defines allostasis as “the ability of the body to achieve stability through its own regulatory changes.” Allostasis is affected by diet, sleep, exercise, whether or not we drink or smoke, and even our socioeconomic status. “If our allostatic load is high, our bodies work overtime to maintain balance.”

The idea of checks and balances in the stress response brings us to the final way in which the protective systems of allostatis can trigger the damage of allostatic load: when the stress response is insufficient, resulting in underproduction of the stress hormones, particularly cortisol, wear and tear can also result.…How can this be? Surely if there are no stress hormones, there must be no stress and consequently no stress-related illness. But like most of human physiology, it isn’t quite that simple. Cortisol acts somewhat like a thermostat; in fact, it clamps down on its own production. It slows the production of the two hormones that touch off the HPA (hypothalamus-pituitary-adrenal) axis: corticotropin-releasing factor in the hypothalamus and adrenocorticotropic hormone in the pituitary. Cortisol also reins in the immune system and reduces inflammation and swelling from tissue damage.

When one of the participants in a checks-and-balances arrangement isn’t doing its job, the others may go overboard in doing theirs. In some people, allostatic load takes the form of a sluggish response by the adrenals and a subsequent lack of sufficient cortisol. The most immediate result is that the immune system, without cortisol’s steadying hand, runs wild and reacts to things that do not really pose a threat to the body. Allergies are one example of this process. In most people the immune system does not put things like dust and cat dander on a par with pathogenic (disease-causing) bacteria. But in people prone to allergies, the immune system goes on red alert in the presence of such usually innocuous substances, throwing everything it’s got at the irritants: uncontrollable sneezing to expel the invaders, mucous secretion to entrap them, swelling caused by the influx of white blood cells to the infected area, pain, redness, and general misery. All of these symptoms are reduced by the action of cortisol.…

A feeble HPA response can often manifest itself in conditions not always immediately associated with the immune system. Fibromyalgia, for example, is a condition of chronic pain that most doctors consider psychosomatic (and some consider imaginary, though the patients certainly don’t). The connection with the immune system and cortisol becomes clear when we consider that pain is a part of the inflammatory response; pain warns us that there’s a problem and encourages us to leave the affected area alone until the problem is resolved. But in many chronic pain states, as with other inflammatory disorders, there is no apparent threat. Rather, the system is responding in a maladaptive way, which the available supply of cortisol is too low to prevent.

(Excerpted from The End of Stress as We Know It, by Bruce McEwen, with Elizabeth N. Lasley. Dana Press/Joseph Henry Press, Washington, DC, 2002.)