Allostatic Load: Quantifying Chronic and Long-Term Intermittent Stress to Improve Health and Well-Being in Animals
“After decades of resistance, there is now a genuine consensus that disease cannot be prevented or even successfully treated unless the role of stress is addressed alongside traditionally recognized factors such as genes and the environment.”1
Practitioners of zoological medicine have long known that the stress of nonnative environments, unusual social groupings, human proximity, and space restriction can lead to immunosuppression and compromised health. To date, metrics for stress have been limited primarily to evaluation of circulating glucocorticoid levels in blood, saliva, urine, and feces. In human medicine, the impacts of chronic stress on physiologic dysregulation, termed allostatic load, have been evaluated using a composite of biomarkers known as the allostatic load index (ALI). Measures of ALI are based on physiologic adaptation to stress which, when repeatedly or chronically stimulated, leads to systemic dysfunction and disease.1,2 In humans, ALI is calculated using a panel of biomarkers of cardiovascular, metabolic, and immunologic health and is associated with both numerous health disorders and increased risk of mortality.3 Recently, the ALI model has been adapted for nonhuman primates and shows promise as a measure of chronic stress in these species. In western lowland gorillas (Gorilla gorilla gorilla) in human care, for instance, ALI is directly related to age, sex, and stressful events,4 and wild-caught females demonstrate higher ALI than those mother-reared in zoologic institutions.5 Adaptation of ALI to wildlife species will require species-specific assay validation and ongoing biomarker evaluation, but it promises to yield an invaluable tool for predicting and preventing stress-related disease and improving well-being in these treasured animals.
1. Duong MT, Bingham BA, Aldana PC, Chung ST, Sumner AE. Variation in the calculation of allostatic load score: twenty-one examples from NHANES. J Racial Ethn Health Disparities. June 2016; doi: 10.1007/s40615-016-0246-8.
2. Edes AN, Crews DE. Allostatic load and biological anthropology. Am J Physical Anthrop. 2016; doi 10.1002/ajpa23146.
3. Edes AN, Wolfe BA, Crews DE. Assessing stress in zoo-housed western lowland gorillas (Gorilla gorilla gorilla) using allostatic load. Int J Primatol. 2016a;37:241–259.
4. Edes AN, Wolfe BA, Crews DE. Rearing history and allostatic load in adult western lowland gorillas (Gorilla gorilla gorilla) in human care. Zoo Biol. 2016b;35:167–173.
5. McEwen BS, Stellar E. Stress and the individual: mechanisms leading to disease. Arch Intern Med. 1993;153:2093–2101.