Hormones & Vulnerability to Stress
We can thank engineering for many of the terms currently used to refer to stress. Breaking point, tension, strain, elasticity, resilience, and of course stress, come to mind. Arguably, Hans Selye established the trend during the 1930s, when he first introduced the term stress to describe the relationship between the stress hormone cortisol and its negative effects on the health of rats.
Today, the relationship between stress and illness is much better understood. In terms of the way the body responds to a perceived threat we have a fairly good idea of the process and this begins with a system known as the hypothalamic-pituitary-adrenal axis, or HPA. The HPA axis is a sophisticated relationship between the hypothalamus, the pituitary gland and the adrenal glands.
The hypothalamus is an area of the brain that controls most of the body's hormonal systems. When a person perceives danger, cells in the hypothalamus produce hormone corticotrophin-releasing factor (CRF). This starts a chain reaction of hormones that include adrenaline and cortisol. The purpose of these and other hormones is to prepare the body to escape danger. The hormonal cocktail simultaneously boosts heart rate, respiration and the availability of glucose to fuel muscles whilst slowing down bodily systems that aren't required for fight or flight, notably digestion and some parts of the immune system.
The HPA operates like a thermostat, switching in when dangers are perceived and adjusting when they are not. The problems really begin when a person is under real or perceived threat almost constantly. When this occurs the balance of the body is thrown out and systems remain on alert. Mechanisms such as the immune and digestive systems that should operate naturally during periods of calm are compromised as the HPA ‘thermostat' remains stuck in the on position.
Following a stressful experience it can take up to an hour for levels of cortisol to return to normal levels. If stress remains constant, cortisol levels can have a marked effect on the body. For example, it can prevent the growth of new neural tissue in parts of the brain that should help to switch off the HPA axis. We also know that stress hormones can impair memory formation and may have an effect on the person's ability to put emotional memories into context (Sapolsky, 1994 cited in Wargo, 2007).
Abusive and neglectful childhoods are common characteristics of people who suffer with depression in adulthood. The amount of stress we experience in early life appears to tune our level of sensitivity to stress later in life (Wargo, 2007). According to Wargo, it is even possible to locate the area of the brain responsible for this tuning mechanism, which he describes as, "at the top part of the HPA axis".
Elevated levels of stress-related hormones are found in the spinal fluid of people with depression. Physical changes in parts of the brain associated with stress have been found in suicides. And, as Wargo goes on to state, there is evidence to suggest that, "the degree of maternal care predicts trait anxiety and the responsiveness of an individual's HPA axis to stress".
Does all this mean that stress in inevitable in some and less so in others. Well, no to both. It remains the case that a person's situation and lifestyle have a powerful effect on a person's coping mechanisms and even if you have been short-changed at an early age or possibly inherit greater vulnerability to stress, it is still possible to influence outcomes.
Wargo, E (2007) Understanding the Have-Knots: the role of stress in just about everything. APA Observer. 20, 11, 18-23.