Why are the new concepts of allostasis and allostatic load important for researchers and relevant to research in public health?  At FICAP, much of our area of interest in injury and violence spans biology, behavior and environment. Integrating the complexity of these concepts in injury science is challenging. As we looked at the new directions in research on stress and chronic diseases, it struck us that these same mechanisms might be relevant to intentional and unintentional injuries, as well.   Drs. Sterling and McEwen originated the concepts and produced the seminal work in allostasis and allostatic load respectively.  These concepts are necessary to understand stress and illness. Lay use of the word "stress" does not translate well into science and its meaning varies across disciplines.  Our speakers will explain the concepts of allostasis and allostatic load and why they are significant.  We are delighted that they are willing to join us in exploring how these concepts might inform new directions in injury research.

Homeostasis, the standard model in physiology and medicine, states that each key parameter is clamped to a "setpoint" with acute deviations corrected by negative feedback. This model implies that chronic deviations reflect broken mechanisms and suggests therapies to restore "inappropriate" values to "normal".

Evidence now accumulates against this model: (i) parameters actually vary; (ii) variations do not signify error but, rather, the brain's effort to prevent error; (iii) homeostasis cannot explain prevalent diseases, such as essential hypertension, type 2 diabetes, and addictions – where mechanisms are not broken, and where drug treatments directed at low-level mechanisms are ineffective. Allostasis, a new model, emphasizes that the goal of regulation is not constancy, but efficiency, which requires preventing errors and minimizing costs. Both needs are best accomplished when the brain uses prior information to predict demand and then adjusts all parameters to anticipate it. Allostasis treats unusual parameter values, not as failures to defend setpoint, but rather as responses to some prediction. The model attributes essential hypertension, type 2 diabetes, and addictions to sustained neural signals that arise from unsatisfactory social interactions. Consequently allostasis would redirect therapy, away from manipulating low-level mechanisms, toward improving higher levels with the goal of restoring predictive fluctuation - which is the hallmark of health.

Stress, whether dramatic or a series of events in daily life, exacts a toll by elevating the activities of the mind and body's physiological systems, causing wear and tear on the brain and many body systems.  This wear and tear is called allostatic load. It reflects the impact of how negative life events, genetic factors, individual behaviors, and developmental experiences shape life long patterns of reactivity by the systems that produce physiological stress mediators. While the neuroendrocrine hormones associated with stress and allostatic load are adaptive and protect the body in the short run, changes in the long run increase mortality and disease, particularly for those coping with a lifetime of limited resources and negative life events.  The allostatic load that results from psychosocial challenges related to competition in social hierarchies has been found to promote poor health and chronic disease.  Its impact on cognitive function and behavioral adaptations may also affect risk-taking and promote self-injurious behaviors as well as hostility and aggression.