What is stress? The term was adopted from engineering for use in biology in the 1920s [Start here for the full presentation]:
Eighty-some-odd years ago, only buildings and bridges could be under stress, technically speaking. Back then, “stress” was strictly an engineering term that referred only to mechanical forces acting on physical structures.
In the 1920s, physiologist Walter Cannon first used the term “stress” to describe the body’s response to unpleasant conditions. Cannon also identified and named the “fight or flight response.” But it was Dr. Hans Selye who popularized the term “stress” and noted its deleterious effects on health.
In his book, Why Zebra’s Don’t Get Ulcers, Robert Sapolsky describes how Selye’s bad lab technique led to his good idea. Legend has it, Selye was testing the effects of a hormone by injecting it into a group of rats. But Selye had trouble injecting the animals, and wound up traumatizing them on a daily basis, causing the rats to develop ulcers, enlarged adrenal glands and atrophied immune tissues.
How did Selye know it was the stress of the injections causing the physical changes and not the hormone under consideration? Selye’s control group of rats-which received a daily injection of harmless saline-developed the same illnesses by the end of the trial.
Stress is not necessarily a bad thing. In fact, it serves an important biological function, and it can help our body focus its energy on short-term tasks:
In moderate amounts, the scientists argue, stress can be benign, even beneficial, and most people are equipped to deal with it.
Preparing to give a speech, take a test or avoid a speeding car, the body undergoes an elaborate series of adjustments. Physiological processes essential in mobilizing a response — the cardiovascular system, the immune system, the endocrine glands and brain regions involved in emotion and memory — are recruited into action. Nonessential functions like reproduction and digestion are put off till later.
Adrenaline, and later cortisol, both stress hormones secreted by the adrenal glands, flood the body. Heart rate and blood pressure rise, respiration quickens, oxygen flows to the muscles, and immune cells prepare to rush to the site of an injury.
When the speech is delivered, the test taken or the car avoided, another complex set of adjustments calms things down, returning the body to normal.
The problem is that stress responses in the body were probably developed to save us from predators, and are not designed to help us overcome long-term anxieties and pressures.
When stress persists for too long or becomes too severe, Dr. McEwen said, the normally protective mechanisms become overburdened, a condition that he refers to as allostatic load. The finely tuned feedback system is disrupted, and over time it runs amok, causing damage.
Work that Dr. McEwen and his colleagues have conducted with rats nicely illustrates this wear-and-tear effect. In the studies, the rats were placed in a small compartment, their movement restricted for six hours a day during their normal resting time. The first time the rats were restrained, Dr. McEwen said, their cortisol levels rose as their stress response moved into full gear. But after that, their cortisol production switched off earlier each day as they became accustomed to the restraint.
That might have been the end of the story. But the researchers also found that at 21 days, the rats began to show the effects of chronic stress. They grew anxious and aggressive. Their immune systems became slower to fight off invaders. Nerve cells in the hippocampus, a brain region involved in memory, atrophied. The production of new hippocampal neurons stopped.
Dr. Sheldon Cohen, a professor of psychology at Carnegie Mellon University, has found that people respond much the same way. Among volunteers inoculated with a cold virus, those who reported life stresses that continued for more than one month like unemployment or family problems were more likely to develop colds than those who reported stress lasting less than a month. The longer the stress persisted, the greater the risk of illness.
In my next post I’ll explore some of the factors that affect how we handle stress, such as personality, social rank, and the quality of the institutions we live in. And then, after that, get back to discussing what we can do to better manage stress. [Click on the “
health” category link to see all related posts.]