Applying the Allostatic Load Model to Investigate the Biological Embedding of Psychosocial Stress in Firefighters

Abstract

Overview

Psychosocial factors are recognised as a significant source of stress in the workplace, and long-term exposure to such stressors may increase chronic disease risk through physiological wear and tear quantified by an individual’s “allostatic load” (AL). Given that firefighters are critical to public safety, I investigated whether the duty-related psychosocial stressors they experience could affect their long-term health and wellbeing by causing increased levels of allostatic load.

Objectives

I began by consolidating information on work-related psychosocial stressors and related health consequences in firefighters by systematically reviewing the current literature. Next, I applied the allostatic load model, a comprehensive multi-systemic measure of cumulative stress impact, to elucidate the underlying mechanism linking psychosocial stressors to adverse health outcomes. Specifically, the relationship between a firefighter’s perceived psychosocial stress and their AL was investigated cross-sectionally and longitudinally. In addition, the potential influence of specific demographic factors (e.g., age and length of service) and psychosocial resources (e.g., social support) on the psychosocial stress-AL (PS-AL) model was explored. Finally, I sought to determine the prevalence of COVID-19-related pandemic stress in this group and its effect on the investigated association.

Methods

First, a systematic review and meta-analysis of the literature on hair cortisol concentration (HCC) was completed to determine a normal reference value/range in healthy adults as part of the methodological recommendations for the thesis. Second, a systematic review of studies reporting psychosocial stressors and their related health outcomes experienced by firefighters was completed using the MEDLINE, PsychInfo, and CINAHL databases. Third, active firefighters were recruited from Waterloo Fire Rescue to investigate the PS-AL relationship. Data collection took place in two phases, a baseline and a follow-up session. In both phases, firefighters provided demographic and health-related information together with subjective assessments of their work-related stress experiences. Additionally, they provided anthropometric and physiological data representing stress-sensitive features of the neuroendocrine and cardiometabolic systems (for example, hair cortisol, heart rate variability, and lipid biomarkers). Correlational analysis was used in the cross-sectional study to explore associations between key demographic, health, and physiological variables. In addition, a linear regression analysis was used to examine the relationship between psychosocial stress and allostatic load and to investigate the potential modifying effect of social support. Finally, a linear mixed-effect model was applied for the longitudinal analysis to explore the effect of psychosocial stress on allostatic load over time (baseline and follow-up), while accounting for the influence of age, social support, and COVID-19-related stress over the same period.

Results

An HCC reference value of 60.51 pg/mg was determined, and an upper limit (i.e., mean plus two standard deviations) for HCC for healthy adults was set at 241.28 pg/mg. For the systematic review, twenty-nine studies met the inclusion criteria. Firefighters identified a range of unique psychosocial stressors, such as interpersonal conflict and organisational fairness concerns. In addition, these stressors were significantly linked to various adverse health outcomes broadly grouped into six areas: depression-suicidality, non-depressive, mental health problems, burnout, alcohol use disorders, sleep quality, physiological parameters and somatic disorders. The empirical data from the cross-sectional analysis revealed an association between work-related psychosocial stress and allostatic load, but the relationship did not reach the threshold for statistical significance. Interestingly, a firefighter's age significantly predicted allostatic load. In addition, the availability of social support displayed an inverse association with stress (i.e., firefighters who perceived more social support felt less stress than those who did not). The longitudinal analysis of the relationship between psychosocial stress and AL revealed that, after accounting for age, social support, and Covid-related stress, a firefighter’s perceived general-life stress at baseline was significantly associated with an increase in allostatic load after a year (95% CI: 0.01, 0.19; p = 0.04). However, work-related psychosocial stress at baseline did not meet the significance threshold. Moreover, although 48% of participants reported COVID-19-related stress, which was positively associated with general life stress experience, it played no significant role in the psychosocial stress-AL relationship.

Conclusion

Our findings reveal unique psychosocial stressors prevalent within firefighting and how these stressors may progressively affect health and wellbeing. In addition, the results indicate the continued importance of health-promotion interventions within this professional group. Although the study revealed more informative trends than definitive relationships, we believe that the AL model shows promise as a valuable tool for monitoring and preventing the cumulative health consequences of psychosocial stress among firefighters.