The Good, the Bad, and the Ugly of Cortisol Metabolism
The preceding few paragraphs certainly place cortisol in a positive light by focusing on the "good" aspects of cortisol metabolism—and they outline exactly what we would expect from a "normal" pattern of cortisol metabolism (that is, in a perfect world). In that perfect world, cortisol metabolism would look something like this: A stressor is encountered, the endocrine system is activated, the stressor is dealt with, and the stress response is ended. All in all, a very simple reaction. However, when the endocrine system becomes either overactivated or chronically activated (on a regular or repeated basis), the result can be an overall dysregulation of the endocrine system that can lead to a gradual and progressive deterioration of general health and a worsening of existing conditions. So why even have a stress response if it causes so many problems? Good question. Back in our "caveman" days, this stress response was a vital survival technique—and not having such a response would have meant that we were easy prey for saber-toothed tigers and other predators. To repeat how all this works (because it is such an important part of understanding the health problems that arise from chronic stress), the stress response involves a brief increase in energy levels, hormone levels, and ability for forceful muscle contraction—otherwise known as the fight-or-flight mechanism. The phrase "fight or flight" means just what it says: It prepares the body to deal with the stressor by either attacking it or running away from it. Unfortunately, even in these modern times, when we're faced with a "benign" stressor, such as a project deadline or a traffic jam (these may be irritating, but they're not going to swallow you like the aforementioned tiger), our bodies undergo the very same metabolic stress changes—which can lead us down the path to increased disease risks.
Under normal circumstances, the body does a pretty good job of controlling cortisol secretion and regulating the amount of cortisol in the bloodstream—but not always (more on this later). Normal cortisol metabolism follows a circadian rhythm (Figure 3.2)—meaning that levels tend to follow a twenty-four-hour cycle—with the highest cortisol levels typically observed in the early morning (about 6:00 to 8:00 a.m.) and the lowest levels in the wee hours of the morning (about midnight to 2:00 a.m.). Cortisol levels usually show a rapid drop between 8:00 a.m. and 11:00 a.m., and they undergo a continued gradual decline throughout the day. After reaching the lowest levels at around 2:00 a.m., cortisol levels begin to rise again to help us wake up and prepare for another stressful day.
It is interesting to note that people who work the graveyard shift for prolonged periods of time (more than a year) undergo alterations in their "cortisol clocks." Their cortisol levels are lowest during the day, when people who work this shift get their deepest sleep, and their levels start to rise again in the late afternoon to early evening when they must get up and get ready for their night work. This is exactly opposite from the pattern we see in people with "normal" work schedules. However, it is important to note that most shift workers (those who pick up an occasional late shift now and again) show no such adaptation in cortisol metabolism. For these people, the additional late shift merely disrupts sleep patterns and keeps cortisol elevated when it should be falling.
The "normal" range for blood cortisol levels is fairly wide, 6–23 mcg/dl (micrograms per deciliter), but these levels can vary tremendously in response to stress, illness, and even following meals, each of which increases cortisol levels. Blood cortisol measurements are also affected by the time of day at which they are collected, because cortisol levels are usually high in the morning and low at night. Urinary levels of cortisol have an even wider range of "normal" values (10–100 mcg/dl over twenty-four hours), but because urine samples are collected over a twenty-four-hour period, this measurement at least avoids the issue of the large circadian (daily) variations in cortisol levels seen in blood measurements. The problem with measuring cortisol levels in urine is that the range of normal values is huge. Cortisol levels can also be elevated by estrogen hormone therapy, exercise, pregnancy, depression, anxiety, and even by the intake of mild stimulants such as ephedra (used for weight loss) or caffeine (as little as two to three cups of coffee will elevate cortisol levels).
Now, for some of the bad aspects of cortisol metabolism. If the above information makes you think that your "normal" cortisol levels are at risk for becoming elevated, then you're not alone. In fact, with today's Western lifestyles being defined by our fast-paced, low-sleep, fast-food habits, it would be surprising to find people who did not experience elevated cortisol levels on a regular basis. "So what," you say? You're not afraid of no stinkin' cortisol? Well, you should be. To reemphasize yet another point that bears repeating from the earlier chapters, here's why: There is very good scientific and medical evidence to show that chronically elevated cortisol levels are associated with obesity, hypertension, diabetes, fatigue, depression, moodiness, irregular menstrual periods, decreased sex drive, and Alzheimer's disease.
Whenever our bodies are exposed to a stressor, cortisol springs into action to increase levels of fat and sugar in the bloodstream, which can be used by the brain and muscles to deal with the stressor. Normally, cortisol levels are quickly depleted following the stress response. Unfortunately, the way our bodies were designed to deal with stress (fight or flight) is not the way we deal with stress in our modern world, where we simply try to ignore the stress hormones pulsing through our bodies. This scenario means that our bodies are unable to deplete their stores of stress hormones—which induces even more stress and stimulates an even more pronounced secretion of cortisol.
Because our bodies were meant to deal only with immediate short-term exposure to stress hormones, this chronic long-term exposure to cortisol can quickly lead to breakdowns in the body's metabolic control systems. Most of the problems associated with elevated cortisol levels have their origins in a disrupted metabolism, causing elevations in blood sugar, cholesterol, blood pressure, and body-fat levels. This cluster of related metabolic disturbances is termed the metabolic syndrome, or sometimes syndrome X. Many people with syndrome X are easily recognizable because of their accumulation of abdominal body fat (they look apple-shaped) and their high waist-to-hip ratio (WHR). Research has clearly shown that the higher a person's WHR (the bigger one's waist circumference compared to his or her hip circumference), the higher his or her risk for developing syndrome X. An optimal WHR is usually considered anything under 0.8 (meaning a smaller waist than hip circumference), while anything over 0.85 puts a person at risk for syndrome X (more on syndrome X is presented in Chapter 6).
Recall from Chapter 1 (in the section titled "Stress and Disease") how one of the most notable effects of chronically elevated cortisol levels is an increase in appetite and cravings for certain foods. These cravings tend to be for calorie-dense sweets and salty snacks—and this illustrates in one more way the fact that human beings were simply not meant to carry around constant disturbances in our stress response (chronic stress); we were built to respond to stress quickly and then to have those stress hormones dissipate immediately. When our bodies are exposed to wave after wave of the stress that comes from modern lifestyles, our bodies gradually begin to break down. Animals simply don't normally harbor chronic stress the way humans do.