Allostasis and Allostatic Load and Chiropractic’s Role

(From the December 2008 “G”Note)

The concepts of allostasis, allostatic load, and allostatic overload have become important in the understanding and quantification of wellness and health and the effect of stressors on the body. It is a foundation concept of the ICA Wellness program. What do those terms mean, and how do they fit into chiropractic? This is a very brief primer on a topic that should be of interest to Gonstead chiropractors who espouse health optimization or wellness.

A basis of the chiropractic principle is homeostasis. According to Dorlands, homeostasis is “tendency to uniformity or stability in the normal body states of the organism.” (Agnew et al) Tolekova et al call it “dynamic equilibrium.” (Tolekova) The chiropractic goal is to help the restore and maintain it and allow necessary and appropriate fluctuations in response to the environment through optimal nerve function that directs the response.

Environmental challenges to the organism requires adaptive strategies to restore or maintain homeostasis – to achieve stability by making appropriate physiological alterations in response to challenges from the environment. This is called allostasis – “maintaining stability through change.” (McEwen Feb 2000, Oct 2000, Schulkin) Maintaining stability is a complex process that is not local but involves the entire body, in particular, the nervous and endocrine systems. Some call the process the stress response. (Dallman) Some find the terms stress response and stress to be ambiguous as these terms do not bring to mind negative lifestyle practices and choices, such as, smoking, inadequate rest, physical inactivity, etc. (McEwen & Winfield) The responses and adaptation to daily life requires the interaction of, in particular, the neuroendocrine system, autonomic nervous system, and the immune system. (McEwen Oct 2003) Changes to the regulatory system that maintains homeostasis can have behavioral and physiological responses. (Schulkin) For example, if the body requires fluids, one senses thirst and tries to sate it.

Schulkin states that the central nervous system helps orchestrate bodily viability and is key in superceding local physiological processes to maintain tissues health. (Schulkin) For this reason, an optimally functioning nervous system is necessary for the tissues and the organism.

In the nervous system, neurotransmitters are released that can stimulate or inhibit neuronal activity in response to stimuli to receptors associated with them. The actions of the neurotransmitters and hormones that are released in the adaptive process are stopped and removed from intracellular spaces by metabolic processes or re-uptakers when not required. (McEwen Oct 2000) Glucorticosteroids, adrenalin, cytokines, DHEA, and catecholamines are a few of the body’s chemicals that mediate physiological changes to maintain stability. (McEwen Oct 2003)

The neurotransmitter and hormone mediators are effective agents for adaptive responses in the short term. If they are not stopped or eliminated and their activity continues, receptor desensitivization or tissue damage in the target tissues or organs may occur. This process is called allostatic load or state. (McEwen 2000, Oct 2003) Allostatic load can be the result of repeated events that cause repeated responses, non-adaptive, chronic or continued, or inadequate responses. This sounds like Palmer’s concept of “too much or too little tone.” As McEwen states, “allostatic load refers to the ‘cost’ of adaptation. (McEwen Oct 2003) It is an important factor in the aging process. (McEwen Oct 2003)

Allostatic overload is another term used wherein the load continues to be excessive or inadequate beyond physiological ranges. Researcher have come up with two categories of allostatic overload. (Schulkin) These categories are quite broad and require further development. Energy balance varies between individuals and must be taken into consideration to further delineate the two types. (McEwen & Wingfield)

Type I: associated with compromised health and reproductive capabilities due to a diminished capacity to sustain physiological and behavioral resources.

Type II: a reflection of the social milieu in which one lives, in our case, the excesses of modern life.

When there is sustained allostatic overload, the result is a chronically higher set point of the body or allostatic load. In chiropractic, when adaptive changes/allostatic load becomes chronic and leads to allostatic overload, chiropractors refer to this as dis-ease.

Among the mediators, cytokines have actions associated in acute injury and immune response. There are inflammatory cytokines, such as, interleukin-1 (IL-1), IL-2, IL-6, and interferons, and anti-inflammatory cytokines include IL-4 and IL-10. An example of inflammatory cytokine’s action is the feeling of sickness and sleepiness during infectious processes. Allostatic load or overload where cytokines play a factor can result in fibromyalgia, diabetes type 1, rheumatoid arthritis, and chronic fatigue syndrome. (McEwen Oct 2003)

Catecholamines, such as, norepinephrine and epinephrine, are important mediators in the allostastic process. In the cardiovascular system, these mediators adjust heart rate and blood pressure. Repeated surges in blood pressure can cause allostatic load that can promote atherosclerosis, and in conjunction with other hormones, type 2 diabetes. (McEwen & Seeman 1999)

Glucocorticoids from the adrenal glands are a part of the process to convert proteins and lipids into usable forms of carbohydrates which are necessary for short term energy output. It is also associated with appetite and the behaviors and activities associated with sating appetite. e.g, deciding to go to the refrigerator for that tub of ice cream. A sedentary existence, wherein one continually reaches for junk food, can cause chronically elevated glucocorticoid levels which lead to elevated insulin levels, and the elevated levels of those hormones together can lead to fat deposition, as well, as arterial plaques. (McEwen Feb 2000) Glucocorticoids can also suppress the inflammation and the immune response. (McEwen Oct 2003)

This brings us to the hypothalamus-pituitary-adrenal (HPA) axis. The hypothalamus is associated with visceral, autonomic, and endocrine functions. It is involved in emotional and affective behavior as well. (Carpenter) The functions of the HPA axis are aided by catecholamines. (McEwen Oct 2003) Hormones of the HPA axis are key components of the adaptative response, such as the above example of glucocorticoids. The hypothalamus has extensive direct and indirect interconnections with the cerebellum. (Zhu et al 2006) The cerebellum is classically known for motor functions. Researchers have found autonomic and cognitive functions as well. (Schuhmann) The cerebellar-hypothalamic connections and feedback are thought to significantly influence the HPA axis. In the GI tract, sensory information is sent to the hypothalamus. It may then go to the cerebellum which may integrate the information and result in feelings of hunger, saity, and thirst and contribute to allostatic responses. Overactivity in the HPA axis when combined with overactivity of excitatory neurotransmitters can cause a form of allostatic load that result in cognitive dysfunction wherein there can be neuronal atrophy and neuronal death. (McEwen & Seeman 1999)

What does this have to do with vertebral subluxations and adjustments? From what we understand, vertebral subluxations cause alterations to the neural structures in and around the spine. Malposition and altered joint motion affects mechanoreceptors in the joint capsules, outer anular layers, muscle and ligaments, and a multitude of other structures. Compression or irritation of the nerve root and branches may have noxious manifestations that alter nerve function. These are stressors that the body must respond to. If the vertebral subluxation becomes chronic, that obviously is a major contributor to allostatic load.

How can adjustments affect the allostatic load. As we know, the adjustment force alters the joint and motion dynamics and tears cross-grained scar tissue. This can reduce the noxious nerve input to the central nervous system and the hormonal/chemical response by the body.

Science calls the alterations from homeostasis due to adaptive responses to the environment, allostasis and its process: allostatic load. Chiropractors call it dis-ease. The body needs to response effectively to its environment. An optimally functioning nervous system, intake of life-sustaining raw materials (good nutrients and clean water and air), regular physical activity, sufficient recovery rest, and active, positive mental activity are necessary to allow for appropriate allostastic or stress response and maintain homeostasis. This is, of course, the foundation principle of chiropractic.

References

Agnew LRC, Aviado DM, Brody JI, et al. (eds) Dorlands Illustrated Medical Dictionary. Philadelphia: W.B. Saunders Co. 1965.

Carpenter MB. Core Text of Neuroanatomy (4th ed). Baltimore: Williams & Wilkins. 1991.

Dallman MF. Stress by any Other Name …? Hormones Behavior Jan 2003; 43(1):18-20.

McEwen BS. Allostasis and Allostatic Load: Implications for Neuropsychopharmacology. Neuropsychopharmacology Feb 2000; 22(2):108-124.

McEwen BS. Allostasis, Allostatic Load, and the Aging Nervous System: Role of Excitatory Amino Acids and Excitotoxicity. Neurochemical Res Oct 2000; 25(9-10):1219-1231.

McEwen BS. The Neurobiology of Stress: From Serendipity to Clinical Relevance. Brain Res Dec 2000; 886:172-189.

McEwen BS. Interacting Mediators of Allostasis and Allostatic Load: Towards an Understanding of Resilence in Aging. Metabolism Oct 2003; 52(10, Suppl. 2):10-16.

McEwen BS, Seeman T. Protective and Damaging Effects of Mediators of Stress: Elaborating and Testing the Concepts of Allostasis and Allostatic Load. Ann N Y Acad Sci Dec 1999; 896:30-47.

McEwen BS, Wingfield JC. Response to Commentaries on the Concept of Allostasis. Hormones Behavior Jan 2003; 42(1):28-30.

Schmahmann JD, Caplan D. Cognition, Emotion and the Cerebellum. Brain Feb 2006; 129(2):288-292.

Schmahmann JD, Sherman JC. The Cerebellar Cognitive Affective Syndrome. Brain Apr 1998; 121(3-4):561-579.

Schulkin J. Allostasis: A Neural Behavioral Perspective. Hormones Behavior Jan 2003; 43(1):21-27.

Tolekova A, Popov B, Ivanov T. Schematic Illustration of Some of the Mechanisms for Maintenance of Homeostasis in Organism. Medical Hypotheses Apr 2003; 60(4):505-508.

Zhu J, Yung W, Chow BK, et al. The Cerebellar-Hypothalamic Circuits: Potential Pathways Underlying Cerebellar Involvement in Somato-Visceral Integration. Brain Research Rev 30 Aug 2006; 52(1):93-106.