CONTEMPORARY PHYSIOLOGICAL APPROACHES
TO STRESS – ALLOSTATIC LOAD AND HEALTH
Building on the work of Selye is an important contemporary approach to stress,
introduced by McEwen and Stellar (1993), which helps us understand how stress can
cause illness over a lifetime. This approach attempts to provide a complete physiological
account of the various bodily systems that may be affected by stress and how different
stressful situations may impact on health. McEwen (1998) proposed that the long-term
impact of stress, known as allostatic load-affects the body at cardiovascular, metabolic,
neural, behavioural and cellular levels. Similar to basic homeostatic systems such as body
temperature, the HPA axis, the autonomic nervous system and the cardiovascular,
metabolic and immune systems protect the body by adapting to internal and external
stress. This is known as allostasis. However, if the activation of these systems is repeated
and prolonged, allostatic load will be experienced in the form of increased release of
stress hormones, immune cells, brain activity and cardiovascular response. It is suggested
that if a person experiences allostatic load for a long time, they are at increased risk of
developing disease because the bodily systems will stop working as effectively (for a
full account see McEwen, 1998, 2007). Indeed, this has been confirmed by a number
of recent studies. For example, a large-scale prospective study, using a comprehensive
measure of allostatic load, found that participants with higher allostatic load scores had
a greater risk of having died 10 years later (Hwang et al., 2014).
In terms of allostasis, when we encounter a psychological or physical stressor (e.g.
giving a speech or encountering an infection or a physical threat), our body has a
twofold response. First, it initiates an allostatic response that activates the stress response
(as described in Chapter 2). Second, when the stressor has passed, the allostatic response
is terminated. As you already know, activation of these systems leads to the release of
several stress hormones including cortisol and changes in blood pressure and heart rate,
which normally return to baseline levels when the stressful encounter has ended.
However, if the allostatic response is not shut off but is maintained over time, due to
inadequate coping, this will result in allostatic load, thus placing excessive pressure on
our bodily systems.
McEwen has suggested that four situations are associated with allostatic load. Each
situation differs in terms of how often we encounter stressful situations and whether
we can cope with them:
1 repeated ‘hits’ from multiple stressors;
2 lack of adaptation;
3 prolonged response; and
4 inadequate response.
As shown in Figure 3.1, the first situation is when we experience frequent stressors.
If these are sustained over long periods of time they can trigger repeated elevations in
blood pressure, thereby increasing the risk of having a heart attack or speeding up the
early stages of heart disease. The second is where we are unable to cope with or to
adapt to the same type of stressor and as a result our body is exposed to stress hormones
for a long period of time. The third condition is when our bodily systems are exposed
to the stress response over an extended episode due to a delayed shutdown of the body’s
48 STRESS AND HEALTH