Effects of allostatic overload on body organs and systems.
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CHAPTER 2 Homeostasis, Allostasis, and Adaptive Responses to Stressors 23
and anxiety and several other diseases (e.g., cardiovascular disease, diabetes, and cancer) also have been associated with shortened telomeres. This research suggests a mechanism by which stress may contribute to cell death and disease, because telomere shortening may be connected to some extent to elevated cortisol, catecholamine, and inflammatory cytokine levels produced as part of the stress response. On the other hand, telomerase is an enzyme capable of lengthening telomeres and is inversely related to perceptions of stress. In one study, 30 men and women took part in a 3-month meditation retreat program aimed at reducing psychological distress. By the end of the study period, the participants had significantly higher telomerase activity levels in comparison to wait-list controls. In another study, adherence to com- prehensive lifestyle changes involving stress management, aerobic exercise, nutrition, and social support were associated with greater telomere length at 5 years after study initiation in men with prostate cancer in comparison to a control group. More research is needed to understand the relationships among telomeres, telomerase, stress, stress-related diseases, and coping methods, as well as aging and longevity.
abuse and neglect have been associated with signs of inflammation, including elevated levels of IL-6, TNF-α, and CRP later in adulthood and older age. Inflammation may partially explain the relationship between childhood stress and some later-life illness conditions, including cardiovascular disease, type 2 diabetes, and some forms of cancers. Many other diseases also are associated with chronic inflammation: Alzheimer disease, chronic inflammatory bowel disease, depression, PTSD, osteoporosis, rheumatoid arthritis, asthma, and periodontal disease, to name but a few. Wound healing also is impaired by multiple mediators of stress in excessive amounts.
Epigenetics is emerging as a new area of study, with epigenetic changes providing a link between some types of stressors and disease pathologies. Epigenetics refers to modifications in gene activity that do not entail altering the basic DNA sequence. These modifications may involve chemical tags or markers on the DNA that can turn a gene on or off. Examples of the mechanisms include DNA methylation, histone modification, and microribonucleic acid (miRNA) gene expression regulation. For instance, adverse childhood events have been associated with DNA methylation in adults and consequent production of IL-6. It is possible that epigenetic changes acquired as a result of early life adverse experiences such as famine or poor maternal attachment and care may make the person susceptible later as an adult to respond to stressors in ways that are adaptive in a threatening environment but maladaptive in a more friendly situation. As an example, a person prone to responding to stressors with a heightened sense of vigilance and arousal may find this response helpful in the dangerous situation, but it may lead to anxiety and depression when repeatedly used in a safer environment.
Another new area of stress research attracting attention pertains to telomeres and telomerase. Telomeres are the tail ends of chromosomes that get shaved down with repeated cell division; and thus older cells tend to have shorter telomeres than younger ones. These cells with shortened telomeres are more susceptible to death. Telomeres are both markers and mechanisms of biological aging and may serve as a means of measuring a person’s total accumulated exposure to stressors. Chronic stress related to caregiving, lower SES, and number of childhood adversities has been linked with shorter telomere length. Depression
KEY POINTS • Adaptation, or allostasis, is a network of biopsychosocial processes of
responding to a stressor with the goal of reestablishing homeostasis. Coping mechanisms are usually seen as behavioral adaptations to stress, but are often used interchangeably with adaptation; they can contribute to resilience.
• The wear-and-tear effect of adaptation on the body and mind is the allostatic load. It occurs as mediators produced by the stress response systems accumulate and contribute to tissue damage over time. Allostatic load reflects the cumulative costs of adaptation.
• A number of disorders are thought to be related to excessive stress or inappropriate stress responses—allostatic overload. These are a result of the dysregulation and excessive use of the mechanisms and mediators involved in the stress response.
Homeostasis is the state of balance of the body’s biopsychosocial systems. Stressors evoke a stress response and initiate adaptive efforts, an allostatic process, designed to return to this steady-state. The response to stressors is affected by a wide variety of factors. Recently there has been an increase in knowledge regarding the complex interactions of the HPA axis, the SNS, the immune system, genetics and epigenetics, and the chemical mediators of the stress response.
Excessive or prolonged stress and overactivity or underactivity of associated chemical mediators produce disproportionate responses in the body, a condition of allostatic overload known as stress-induced illness. As humans strive to adapt to the constant changes of modern life, the study of stress and stress-related disease has become vital to public health and contributes to the development of increasingly sophisticated models of health and illness.