The Relationship Between Stress and Disease
So now you know a bit about how chronic stress leads to elevated cortisol and reduced testosterone levels in the body. This chapter details the next piece of the puzzle: the relationship between cortisol/testosterone ratios and the risk for a wide range of chronic diseases. For the sake of simplicity, when I refer to "elevated cortisol levels" or to "cortisol overexposure," you should assume that I am referring not only to excess cortisol, but also to suboptimal testosterone. It should come as no big surprise to anybody reading this book that the effects of stress on a person's long-term health can be far-reaching. The medical literature tells us quite clearly that many of the negative conditions associated with a "modern" lifestyle-such as obesity, diabetes, hypertension, insomnia, headaches, ulcers, depression, anxiety, poor memory, and a lower resistance to infections—are all related to high stress levels. Also noteworthy is the consistent finding that people dramatically increase their use of the medical system during times of heightened stress (such as a period of job insecurity) and that there is a tight association between elevated cortisol levels and higher health-care costs. Episodes of illness, doctor visits, and trips to hospital outpatient departments have been shown to double (at least) during high-stress periods when compared to lower-stress periods. We see the same pattern emerge during final-exam week on college campuses, when walk-in health clinics are filled with sick students during their most stressed-out time of the year. Other evidence clearly demonstrates that workers reporting the highest level of perceived stress due to job dissatisfaction, family problems, and personal conflict are the most likely to experience somatic symptoms such as colds, flu, allergies, asthma, and headaches.
Metabolic Consequences of Elevated Stress Levels
Okay, so cortisol is toxic—right? Not so fast. As we know from the previous chapters, cortisol is a vital hormone; without it, the body would be ill prepared to deal with the stresses of daily life. On the other hand, excess cortisol secretion and chronically elevated cortisol levels can lead to a host of related metabolic disturbances and an increased risk for developing a variety of chronic conditions. We touched on many of these effects in the preceding chapters, and they are summarized here in Table 6.1.
Table 6.1: Metabolic and Long-Term Health Effects of Elevated Cortisol Levels
- Metabolic effect (cortisol-induced) Chronic health condition
- Increased appetite, accelerated muscle catabolism (breakdown), suppressed fat oxidation, enhanced fat storage Obesity
- Elevated cholesterol and triglyceride levels Heart disease
- Elevated blood pressure Heart disease
- Alterations in brain neurochemistry (involving dopamine and serotonin) Depression/anxiety
- Physical atrophy (shrinkage) of brain cells Alzheimer's disease
- Insulin resistance and elevated blood-sugar levels Diabetes
- Accelerated bone resorption (breakdown) Osteoporosis
- Reduced levels of testosterone and estrogen Suppressed libido (reduced sex drive)
- Suppression of immune-cell number and activity Frequent colds/flu/infection
- Reduced synthesis of brain neurotransmitters Memory/concentration problems
Stress-related diseases occur because of an excessive activation of the stress response in the brain and in the endocrine (hormone) system in reaction to common, everyday sources of physical and psychological stress. The various daily stressors to which we are all subjected can disrupt the body's stable balance of temperature, blood pressure, and other functions. Unfortunately, as mentioned before, because the human brain is so well developed, it can also respond to imagined stress with the very same stress response that is supposed to be reserved for life-or-death (fight-or-flight) situations. Accordingly, injury, hunger, heat, cold, or worry can trigger the stress response just as would happen if you were running for your life or fighting off an attacker.
In 1999, a team of Swedish researchers showed that exposure to high levels of stress caused a rapid increase in cortisol secretion, followed by reduced sex-hormone levels and depressed libido (sex drive). That same year, a report from the New York Academy of Sciences suggested that elevated cortisol levels, caused by exposure to perceived stress, were associated with development of the metabolic syndrome (a.k.a. syndrome X) described in earlier chapters, which is characterized by insulin resistance, diabetes, abdominal obesity, elevated cholesterol, and hypertension. Research published in 2000 by scientists at Yale University supports the idea that emotional stress contributes to weight gain in both overweight and lean women. The researchers noted that the connection between stress and obesity is most likely due to an excessive secretion of cortisol and the adverse metabolic effects of the hormone in people with chronically elevated levels. Elevated cortisol levels are also associated with reduced levels of testosterone and IGF-1 in men exposed to high stress. (IGF-1, or insulin-like growth factor 1, is a hormone related to growth hormone.) Because both testosterone and IGF-1 are anabolic or muscle-building hormones, these men also tend to have reduced muscle mass and higher body-fat levels. These same men also tend to have a higher body mass index (BMI), a higher waist-to-hip ratio (WHR), and abdominal obesity (an apple shape). Researchers at the Neurological Institute at the University of California at San Francisco (UCSF) have linked excessive cortisol levels to depression, anxiety, and Alzheimer's disease, as well as to direct changes in brain structure (atrophy) leading to cognitive defects (meaning that cortisol can shrink and kill brain cells).
So, as emphasized throughout this book, cortisol is not all bad—but too much of it for too long is a recipe for disaster. The sections that follow will outline in greater detail the metabolic relationship between elevated cortisol and specific conditions. Be warned: The news is not good for those of us who experience stress on a regular basis; the next section may even leave you feeling as if your high stress levels are killing you (and they are!). There is good news, however, and it starts in Chapter 7, where we'll begin to learn about the various steps that can help us get a handle on our stress response and help us modulate cortisol levels within a more healthful range.