4.8: STRESS
Have you ever been “stressed out” in class? Say you’re in a large lecture hall with a hundred other people, or even in a small class where you don’t know anyone. You’re not sure about something the professor just said and you would really like to ask about it, so you start to raise your hand. Does your heart begin to pound and your mouth get dry? Do you sometimes get so nervous you choose to catch up with a classmate after lecture instead? If so, you are not alone. Fear of speaking in public is one of the most common social phobias (APA 2013). It has been estimated that 75% of all people experience some degree of anxiety or nervousness when it comes to public speaking (Hamilton 2011), and surveys have shown that most people fear public speaking more than they fear death (Croston 2012).
We have evolution to thank for this.
Humans, like other primates, are social animals. Being part of a group helped us to survive predation, get enough to eat, and successfully raise our young. When faced with standing up in front of a group, or even speaking up in class, we break into a sweat because we are afraid of rejection. Psychologist Glenn Croston (2012) writes, “The fear is so great because we are not merely afraid of being embarrassed or judged. We are afraid of being rejected from the social group, ostracized and left to defend ourselves all on our own. We fear ostracism still so much today it seems, fearing it more than death, because not so long ago getting kicked out of the group probably really was a death sentence.” Hence, it is no surprise that public speaking triggers a stress response among much of humankind.
The human nervous system evolved in a context where quick responses to perceived threats presented an evolutionary advantage. The “fight or flight” response with which we are all familiar was honed during millions of years when threats more often took the form of an approaching lion than an approaching deadline. Our body’s response, however, is triggered by a wide variety of stressors that produce the same general pattern of hormonal and physiological adjustments (Martini et al. 2013). In today’s world, the system is often stuck in the “on” position due to the constant pressures of modern life, and this is a significant influence on health and disease.
The human stress response involves the Central Nervous System acting in concert with the endocrine and circulatory systems. It includes three phases: alarm, resistance, and exhaustion (Martini et al. 2013). The alarm phase is the automatic, short-term response to a crisis, the “fight or flight” response you might have experienced when thinking about raising your hand in class. Epinephrine is the dominant hormone of this phase. Its secretion stimulates activation of the sympathetic nervous system, including sudden increases in heart rate, respiration, mental alertness, sweat gland excretion, and energy use. If the stress-inducing situation lasts more than a few hours, the body shifts to the resistance phase. Glucocorticoids are the dominant hormones of this phase, which involves mobilizing the body’s metabolic reserves to maintain the energy levels necessary for the brain to function during continued stress. A side effect of glucocorticoids is suppression of inflammation and the immune response, and cardiovascular damage can occur from elevations in blood pressure and blood volume from the action of ADH (antidiuretic hormone) and aldosterone (a hormone that regulates salt and water in the body). The resistance phase can be maintained for weeks or months, but eventually homeostatic regulation breaks down and leads to the exhaustion phase. If corrective actions are not taken, organs begin to fail, and death follows (Martini et al. 2013).
The negative effects of sustained, elevated cortisol levels on health are well documented. These include higher levels of infectious disease and slowed growth in childhood (Flinn and England 2003) and increased incidence of heart disease, obesity, and diabetes in adults (Worthman and Kuzara 2005). As opposed to what might have been the case in our evolutionary past, many causes of sustained stress in contemporary societies are psychosocial rather than physical threats. These can include an unhappy marriage or frustrations at work (Dimsdale 2008). Stressors can also be more subtle. For example, a recent review of research into the effects of stress on health indicated internalized racism was a significant stressor that was positively associated with alcohol consumption, psychological distress, overweight, abdominal obesity, and higher fasting-glucose levels among minority groups (Williams and Mohammed 2013). Chronic everyday discrimination is also positively associated with coronary artery calcification, elevated blood pressure, giving birth to lower-birth-weight infants, cognitive impairment, poor sleep, visceral fat, and mortality. These effects have been shown to increase morbidity and mortality among members of affected groups.
Epigenetics can also be a factor in how a person is able to deal with stressful situations. Maternal experiences of stress during pregnancy have the potential to permanently alter the physiology of mothers’ offspring, especially the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis regulates metabolism, blood pressure, and the immune response, and these alterations can predispose prenatally stressed individuals to suffer metabolic, cardiovascular, and mental disorders in adulthood (Palma-Gudiel et al. 2015). These experiences carry across generations, with children of Holocaust survivors who experienced PTSD demonstrating similar changes in neurochemistry in the absence of a sustained, traumatic event, as did infant offspring of mothers who developed PTSD during pregnancy after witnessing the traumatic events of 9/11 (Yehuda and LeDoux 2007). Clearly, stress has a profound impact on human health and is one more example of a biological system that is maladaptive in many modern contexts.
