Cortisol, Fatigue, and Insomnia
Mark was a building contractor who liked his job and enjoyed spending time with his family and on his hobbies (snowmobiling in winter and boating in summer). Because of his laid-back attitude, he appeared to be about as low-stress a person as you could ever meet. Unfortunately, he often reported problems with his sleep patterns; most notably, he had great difficulty falling asleep because his mind got going "a million miles an hour" as soon as he retired for the evening. Mark would often wake up in the middle of the night and have trouble dropping off again. The lack of sleep was beginning to affect his work. First of all, he had a hard time getting out of bed on time in the mornings, and then once he was at work he had trouble concentrating on the precise measurements and craftsmanship necessary to do his job. How did Mark finally deal with his stress-induced insomnia and fatigue? To find out, see Chapter 8.
How do you suppose it is that stress can cause us to be fatigued during the day—but also cause us to have trouble falling asleep at night? The "dynamic duo" of chronic fatigue and insomnia would logically seem to be opposite conditions (if you're so tired, why can't you fall asleep?), but they are commonly found together in the two-thirds of the American population who report experiencing chronic stress and who get inadequate sleep. The common element? You guessed it: cortisol. Making matters worse is the fact that insomnia and fatigue often combine with each other in a vicious cycle wherein stress makes it hard to relax and fall asleep, a person's fatigued condition the next day makes stressors harder to deal with, and the additional stress causes even more difficulty falling asleep the next night.
But how, exactly, does cortisol fit into this picture? As we all know by now, cortisol levels are elevated in response to stress, so any stressful events encountered in the late afternoon to early evening will hamper a person's ability to relax and fall asleep that night. If you'll recall, one of the many effects of cortisol is to increase a person's level of alertness—which is exactly what you want to avoid right before bedtime. Also, if you don't get to bed at a reasonable hour (early enough to allow a full eight to nine hours of shut-eye), your cortisol metabolism doesn't get a chance to follow its normal rhythm, which would achieve its lowest point around 2:00 a.m., as illustrated earlier. As a result, you may get only five, six, or seven hours of sleep, and you wake up groggy after having been exposed to higher than normal levels of cortisol throughout the night.
The long-term results of sleeping less than the standard eight hours a night are annoying side effects such as headaches, irritability, frequent infections, depression, anxiety, confusion, and generalized mental and physical fatigue. But it's not just that a lack of sleep leaves you feeling crappy; research shows that even mild sleep deprivation can actually destroy one's long-term health and increase one's risk of diabetes, obesity, and breast cancer. In many ways, sleeping less than eight hours each night is as bad for overall wellness as gorging on junk food or becoming a couch potato.
Remember that cortisol levels normally peak in the early morning (about 6:00 a.m. to 8:00 a.m.) as a way to get a person moving and prepare her to face the challenges of the day. Between 8:00 a.m. and 11:00 a.m., cortisol levels begin to drop, and they continue to gradually decline throughout the day, typically causing us to feel a decrease in energy levels and ability to concentrate sometime around 3:00 p.m. to 4:00 p.m. (the "afternoon slump"). This dip in energy levels is the body's way of saying, "The day is almost over; better get ready for sleep." Unfortunately, instead of getting ready for sleep, our modern lifestyles cause most of us to search for a way to boost our energy levels in the evenings so that we can get through soccer practices, piano recitals, business dinners, and time with our families. Our body clock really wants us to eat our last meal of the day around 5:00 p.m. and to be asleep by 8:00 p.m., but our wristwatch has us awake late into the night. The major problem with our modern "late to bed, early to rise" lifestyles is that our cortisol levels never have enough time to fully dissipate (which is supposed to happen overnight), so our bodies never have a chance to fully recover and repair themselves from the detrimental effects of chronic stress.
The natural rhythm of restful sleep follows a very specific path from the moment your head hits the pillow: breathing slows, muscles relax, heart rate and blood pressure drop, and body temperature falls. The brain releases melatonin (the "sleep hormone") and begins its change from the rapid beta waves (indicating daytime restless wakefulness) to the slower alpha waves (indicating calm wakefulness) and eventually to the still slower theta waves that predominate during the final various stages of sleep. During a full night of sleep, we normally pass through several intermittent stages of sleep: Stage 2 (lasting ten to fifteen minutes), then Stage 3 (lasting five to fifteen minutes), and finally to the deepest portion of sleep in Stage 4 (lasting about thirty minutes), and the most famous portion of the sleep cycle, REM (rapid eye movement), when we dream. This cycle, from Stage 2 to REM sleep, takes an average of ninety minutes to complete and will repeat itself over and over throughout the night. In the absence of alarm clocks, lights, and other interruptions, sleep researchers have found that the natural duration of these repeating sleep cycles (the "physiological ideal") is eight hours and fifteen minutes.
So what happens to those of us who simply can't (or won't) get that much shut-eye? Well, for one thing, blood-sugar levels will rise. Sleep researchers have shown that getting only four hours of sleep per night results in signs of impaired glucose tolerance and insulin resistance—which means that as little as a few nights of cheating on sleep can put a person in a prediabetic state. These changes in insulin action and blood-sugar control are also linked to the development of obesity. Compounding the link between obesity and poor sleep is the fact that levels of both growth hormone and leptin are reduced in people who spend less time in deep sleep. (Leptin is a hormone with important roles in regulating appetite, body weight, metabolism, and reproductive function.) Less growth hormone in the system typically means a loss of muscle and a gain of fat over time, while reduced levels of leptin will lead to hunger and carbohydrate cravings.
Let's look at the case of a typical all-American go-getter; we'll call him Driven Dan. Who's got time for sleep? Dan can't worry about the abstract risks of getting fat, developing diabetes, or contracting cancer—he has work to do, classes to take, bills to pay, soccer practices to attend, yada, yada, yada. Sound familiar? So what's the solution? Perish the thought that our friend Dan should try to do fewer things—you'll get none of that "simplify your life" stuff in this book (despite the fact that it makes perfect sense). In an ideal world, Dan may be able to work seven hours a day, enjoy a short commute to work, and have all the free time he can stand. In the real world, however (the one in which we all live), the more realistic approach for Dan (and for you?) may be to do the next best thing by getting a handle on his cortisol levels, a topic we'll delve into in the next few chapters.