The Science of Stress
Because our modern world rarely requires the evolutionary fight-or-flight response to stress, we deny our bodies their natural physical reaction to stress. Unfortunately, the brain still registers stress in the same way as it always has, but because we no longer react to that stress with vigorous physical activity (fighting or running away), our bodies store the stress response and continue to churn out high levels of stress hormones. Before we know it, we're living the "Type C" lifestyle, characterized by chronic stress and consistently elevated cortisol levels.
In one of the more ironic twists visited upon us humans as "higher" animals, our brains are so "well developed" that our bodies have learned to respond to psychological stress with the same hormonal cascade that happens with exposure to a physical stressor. This means that just by our thinking about a stressful event, even if that event is highly unlikely to actually occur, our endocrine system gets all in an uproar. Bad news to be sure, but the upside to this story is that even though psychological variables can trigger the stress response, good evidence exists that we can also harness the mind to counteract some aspects of the stress response by using biofeedback and similar relaxation techniques.
Many stress physiologists believe that it is our degree of cortisol variability that indicates a healthy stress response: neither high cortisol nor low cortisol, but a cortisol level that fluctuates normally in response to stress and relaxation. Chronically high cortisol is bad and chronically low cortisol is also bad—but "flat" levels seem to be just as bad as either extreme. A cortisol rhythm that is responsive and variable is good—meaning low at night and low when relaxed, but high during acute stress, and high during exercise, and high during a work deadline, but recovering to baseline levels quickly. We do not want cortisol to be chronically anything (high or low or medium), but rather, we want cortisol flux. We want a highly responsive, finely tuned pattern of cortisol activity.
In the last few years, stress research has shifted away from simply measuring whether cortisol levels are "high" or "low" to focus on how those levels fluctuate over time. In many cases of stress overload, a pattern of "flat" cortisol rhythm is observed. This means that cortisol levels are within ranges that we might call "normal," but they do not appear to go up in response to stress, or to fall when we're supposed to be relaxed. The result is that our bodies are constantly exposed to moderate levels of cortisol on a twenty-four-hour basis, a situation that we are learning may be the worst-case scenario for long-term health. For example, people with chronic stress diseases such as chronic fatigue syndrome and fibromyalgia are known to exhibit a "flat" cortisol rhythm, as are sufferers of PTSD and children who have suffered physical abuse. Additionally, German researchers have found that when cortisol rhythms become flattened, the HSD (fat-storing) system (discussed in Chapter 4) kicks into overdrive, so that abdominal fat cells still "see" a high cortisol level (and thus store fat even faster), while the rest of the body "sees" normal ranges of cortisol (albeit at a constant and never fluctuating level).