Early life stress and iron metabolism in developmental psychoneuroimmunology

An estimated 250 million children face adverse health outcomes from early life exposure to severe or chronic social, economic, and nutritional adversity, highlighting/emphasizing the pressing concern about the link between ELS and long-term implications on mental and physical health. There is significant overlap between populations experiencing high levels of chronic stress and those experiencing iron deficiency, spotlighting the potential role of iron as a key mediator in this association. Iron, an essential micronutrient for brain development and immune function, is often depleted in stress conditions. Iron deficiency among the most common nutrient deficiencies in the world. Fetal and infant iron status may thus serve as a crucial intermediary between early chronic psychological stress and subsequent immune system changes to impact neurodevelopment. The review presents a hypothesized pathway between early life stress (ELS), iron deficiency, and neurodevelopment through the hypothalamic-pituitary-adrenocortical (HPA) axis and the IL-6-hepcidin axis. This hypothesis is derived from (1) evidence that stress impacts iron status (2) long-term neurodevelopmental outcomes that are shared by ELS and iron deficiency exposure, and (3) possible mechanisms for how iron may mediate the relation between ELS and iron deficiency through alterations in the developing immune system. The article concludes by proposing future research directions, emphasizing the need for rigorous studies to elucidate how stress and iron metabolism interact to modify the developing immune system. Understanding these mechanisms could open new avenues for improving human health and neurodevelopment for women and children globally, making it a timely and vital area of study in psychoneuroimmunology research.

Post-adoption experiences of discrimination moderated by sleep quality are associated with depressive symptoms in previously institutionalized youth over and above deprivation-induced depression risk

The association of post-adoption experiences of discrimination with depressive symptoms was examined in 93 previously institutionalized (PI) youth (84% transracially adopted). Additionally, we explored whether sleep quality statistically moderated this association. Notably, we examined these associations after covarying a measure of autonomic balance (high/low frequency ratio in heart rate variability) affected by early institutional deprivation and a known risk factor for depression. PI youth exhibited more depressive symptoms and experiences of discrimination than 95 comparison youth (non-adopted, NA) raised in their biological families in the United States. In the final regression model, there was a significant interaction between sleep quality and discrimination, such that at higher levels of sleep quality, the association between discrimination and depression symptoms was non-significant. Despite being cross-sectional, the results suggest that the risk of depression in PI youth involves post-adoption experiences that appear unrelated to the impacts of early deprivation on neurobiological processes associated with depression risk. It may be crucial to examine methods of improving sleep quality and socializing PI youth to cope with discrimination as protection against discrimination and microaggressions.

The impact of psychosocial adversity on brain and behaviour: an overview of existing knowledge and directions for future research

Environmental experiences play a critical role in shaping the structure and function of the brain. Its plasticity in response to different external stimuli has been the focus of research efforts for decades. In this review, we explore the effects of adversity on brain's structure and function and its implications for brain development, adaptation, and the emergence of mental health disorders. We are focusing on adverse events that emerge from the immediate surroundings of an individual, i.e., microenvironment. They include childhood maltreatment, peer victimisation, social isolation, affective loss, domestic conflict, and poverty. We also take into consideration exposure to environmental toxins. Converging evidence suggests that different types of adversity may share common underlying mechanisms while also exhibiting unique pathways. However, they are often studied in isolation, limiting our understanding of their combined effects and the interconnected nature of their impact. The integration of large, deep-phenotyping datasets and collaborative efforts can provide sufficient power to analyse high dimensional environmental profiles and advance the systematic mapping of neuronal mechanisms. This review provides a background for future research, highlighting the importance of understanding the cumulative impact of various adversities, through data-driven approaches and integrative multimodal analysis techniques.

Early-life influenza A (H1N1) infection independently programs brain connectivity, HPA AXIS and tissue-specific gene expression profiles

Early-life adversity covers a range of physical, social and environmental stressors. Acute viral infections in early life are a major source of such adversity and have been associated with a broad spectrum of later-life effects outside the immune system or "off-target". These include an altered hypothalamus-pituitary-adrenal (HPA) axis and metabolic reactions. Here, we used a murine post-natal day 14 (PND 14) Influenza A (H1N1) infection model and applied a semi-holistic approach including phenotypic measurements, gene expression arrays and diffusion neuroimaging techniques to investigate HPA axis dysregulation, energy metabolism and brain connectivity. By PND 56 the H1N1 infection had been resolved, and there was no residual gene expression signature of immune cell infiltration into the liver, adrenal gland or brain tissues examined nor of immune-related signalling. A resolved early-life H1N1 infection had sex-specific effects. We observed retarded growth of males and altered pre-stress (baseline) blood glucose and corticosterone levels at PND42 after the infection was resolved. Cerebral MRI scans identified reduced connectivity in the cortex, midbrain and cerebellum that were accompanied by tissue-specific gene expression signatures. Gene set enrichment analysis confirmed that these were tissue-specific changes with few common pathways. Early-life infection independently affected each of the systems and this was independent of HPA axis or immune perturbations.

Recalibration of the stress response system over adult development: Is there a perinatal recalibration period?

During early life-sensitive periods (i.e., fetal, infancy), the developing stress response system adaptively calibrates to match environmental conditions, whether harsh or supportive. Recent evidence suggests that puberty is another window when the stress system is open to recalibration if environmental conditions have shifted significantly. Whether additional periods of recalibration exist in adulthood remains to be established. The present paper draws parallels between childhood (re)calibration periods and the perinatal period to hypothesize that this phase may be an additional window of stress recalibration in adult life. Specifically, the perinatal period (defined here to include pregnancy, lactation, and early parenthood) is also a developmental switch point characterized by heightened neural plasticity and marked changes in stress system function. After discussing these similarities, lines of empirical evidence needed to substantiate the perinatal stress recalibration hypothesis are proposed, and existing research support is reviewed. Complexities and challenges related to delineating the boundaries of perinatal stress recalibration and empirically testing this hypothesis are discussed, as well as possibilities for future multidisciplinary research. In the theme of this special issue, perinatal stress recalibration may be a mechanism of multilevel, multisystem risk, and resilience, both intra-individually and intergenerationally, with implications for optimizing interventions.

Childhood Experiences of Alternative Care and Callousness/Unemotionality: A Conceptual Model, Scoping Review, and Research Agenda

Individuals with experiences of alternative care (AC; i.e., out-of-home care and institutional care) are at high risk for various mental health and relational problems stemming from exposure to serious attachment disruptions, loss, and complex trauma. Yet, despite the interpersonal context of their significant adversities, surprisingly there is scant research explicitly focusing on callousness/unemotionality (e.g., lack of guilt, callous disregard for others) in this population. This paper provides the first conceptual model for, and systematic scoping review of, callousness/unemotionality in children and young people with experiences of AC. In a comprehensive search of nine databases, 22 articles involving samples of participants in AC or with histories of AC, were identified for inclusion. The pattern of findings revealed that callous-unemotional and psychopathic traits are elevated in children and young people with AC experiences, and positively associated with AC. Moreover, results showed associations between these traits and various psychosocial correlates, most consistently with externalizing and internalizing problems and attachment-related problems. Only two intervention studies were located, one of which found benefits of training and supporting foster caregivers for reducing callous-unemotional traits. These findings are discussed with respect to gaps in the literature, future research directions, and trauma-informed practice to assess and treat callousness/unemotionality in children and young people with experiences of AC.

The Interaction between Psychological Stress and Iron Status on Early-Life Neurodevelopmental Outcomes

This review presents evidence from animal and human studies demonstrating the possible connection and significant impact of poor iron status and psychological distress on neurocognitive development during pregnancy and the neonatal period, with implications for long-term cognition. Stress and iron deficiency are independently prevalent and thus are frequently comorbid. While iron deficiency and early-life stress independently contribute to long-term neurodevelopmental alterations, their combined effects remain underexplored. Psychological stress responses may engage similar pathways as infectious stress, which alters fundamental iron metabolism processes and cause functional tissue-level iron deficiency. Psychological stress, analogous to but to a lesser degree than infectious stress, activates the hypothalamic-pituitary-adrenocortical (HPA) axis and increases proinflammatory cytokines. Chronic or severe stress is associated with dysregulated HPA axis functioning and a proinflammatory state. This dysregulation may disrupt iron absorption and utilization, likely mediated by the IL-6 activation of hepcidin, a molecule that impedes iron absorption and redistributes total body iron. This narrative review highlights suggestive studies investigating the relationship between psychological stress and iron status and outlines hypothesized mechanistic pathways connecting psychological stress exposure and iron metabolism. We examine findings regarding the overlapping impacts of early stress exposure to iron deficiency and children's neurocognitive development. We propose that studying the influence of psychological stress on iron metabolism is crucial for comprehending neurocognitive development in children exposed to prenatal and early postnatal stressors and for children at risk of early iron insufficiency. We recommend future directions for dual-exposure studies exploring iron as a potential mediating pathway between early stress and offspring neurodevelopment, offering opportunities for targeted interventions.

Longitudinal effects of early psychosocial deprivation on macaque executive function: Evidence from computational modelling

Executive function (EF) describes a group of cognitive processes underlying the organization and control of goal-directed behaviour. Environmental experience appears to play a crucial role in EF development, with early psychosocial deprivation often linked to EF impairment. However, many questions remain concerning the developmental trajectories of EF after exposure to deprivation, especially concerning specific mechanisms. Accordingly, using an 'A-not-B' paradigm and a macaque model of early psychosocial deprivation, we investigated how early deprivation influences EF development longitudinally from adolescence into early adulthood. The contribution of working memory and inhibitory control mechanisms were examined specifically via the fitting of a computational model of decision making to the choice behaviour of each individual. As predicted, peer-reared animals (i.e. those exposed to early psychosocial deprivation) performed worse than mother-reared animals across time, with the fitted model parameters yielding novel insights into the functional decomposition of group-level EF differences underlying task performance. Results indicated differential trajectories of inhibitory control and working memory development in the two groups. Such findings not only extend our knowledge of how early deprivation influences EF longitudinally, but also provide support for the utility of computational modelling to elucidate specific mechanisms linking early psychosocial deprivation to long-term poor outcomes.

Attachment dimensions and cortisol responses during the strange situation among young children adopted internationally

Children's attachments to their parents may help regulate their hypothalamic-pituitary-adrenal (HPA) axes. Prior research has largely focused on children with relatively consistent and low-risk caregiving histories, resulting in limited knowledge about the associations between attachment quality and HPA axis reactivity among children who have experienced early adversity. This study investigated whether dimensional measures of attachment quality were associated with HPA responses to the Strange Situation Procedure (SSP) among 64 children ages 11-33 months adopted internationally from institutional or foster care. Children who showed high levels of attachment avoidance exhibited a blunted cortisol response during the SSP. Conversely, children who sought proximity and contact with their adoptive parents exhibited an increase in cortisol reactivity during the SSP, followed by a return to baseline levels after the completion of the procedure. This association was independent of the previously reported association between parental insensitivity and blunted cortisol responses in this sample.

Adoption and trauma: Risks, recovery, and the lived experience of adoption

BACKGROUND

Although a very heterogeneous group, adopted persons may present developmental and mental health problems of varying severity. Pre-placement adversity and trauma have often been linked to these problems. It has been also suggested that adoption itself is a psychological trauma, predisposing the individual to emotional difficulties.

OBJECTIVES

This article examines the links between early adversity, trauma, and adoption. We begin by defining trauma and then describe the way in which pre-placement adversity can undermine neurobehavioral and interpersonal functioning, increasing the risk for long-term psychological difficulties. Next, we examine children's recovery when placed in a stable adoptive home. Finally, we explore adoption as a lived experience, highlighting contextual and developmental factors that facilitate the person's positive or negative attributions about being adopted, leading to varying patterns of emotional adjustment.

CONCLUSIONS

Although pre-placement adversity increases adopted individuals' risk for maladjustment, the human brain and behavior are malleable, and placement in a nurturing adoptive home often facilitates recovery from early adversity, with significant heterogeneity in the extent of recovery within and across domains of functioning. While there is no evidence that early adoption is a trauma for the individual, ongoing negative life circumstances, attachment difficulties, and developmentally-mediated attributions about adoption can undermine the person's self-esteem, identity, relationships, and sense of well-being. Conclusions and suggestions for future research are offered.

Trust and childhood maltreatment: evidence of bias in appraisal of unfamiliar faces

BACKGROUND

Child maltreatment is associated with poorer social functioning and increased risk of mental health problems in adolescence and adulthood, but the processes underlying these associations remain unclear. Although crucial for establishing and maintaining relationships, trust judgements have not been experimentally investigated in children who have experienced abuse and neglect.

METHODS

A community-based sample of 75 children aged 8-16 years with maltreatment documented on the basis of social services records, and a group of 70 peers matched on age, gender, cognitive ability, socioeconomic status, and ethnicity took part in the study. Children completed a trustworthiness face-judgement task in which they appraised the trustworthiness of unfamiliar facial stimuli varying along a computationally modelled trustworthiness dimension.

RESULTS

In line with clinical observations that childhood maltreatment is associated with an atypical pattern of trust processing, children with maltreatment experience were significantly less likely than their peers to rate unfamiliar faces as trustworthy. Moreover, they were more variable in their trust attributions than their peers.

CONCLUSIONS

The study provides compelling experimental evidence that children with documented maltreatment perceive others as less trustworthy than their peers and are less consistent in their estimates of trustworthiness in others. Over time, alterations in trust processing may disrupt the development of social bonds and contribute to 'social thinning' (a reduction in the extent and quality of social relationships), leaving children more vulnerable to environmental stressors, increasing risk of mental health difficulties.

Emotional maltreatment and neglect impact neural activation upon exclusion in early and mid-adolescence: An event-related fMRI study

Child maltreatment gives rise to atypical patterns of social functioning with peers which might be particularly pronounced in early adolescence when peer influence typically peaks. Yet, few neuroimaging studies in adolescents use peer interaction paradigms to parse neural correlates of distinct maltreatment exposures. This fMRI study examines effects of abuse, neglect, and emotional maltreatment (EM) among 98 youth (n = 58 maltreated; n = 40 matched controls) using an event-related Cyberball paradigm affording assessment of both social exclusion and inclusion across early and mid-adolescence (≤13.5 years, n = 50; >13.5 years, n = 48). Younger adolescents showed increased activation to social exclusion versus inclusion in regions implicated in mentalizing (e.g., superior temporal gyrus). Individual exposure-specific analyses suggested that neglect and EM coincided with less reduction of activation to social exclusion relative to inclusion in the dorsal anterior cingulate cortex/pre-supplementary motor area (dACC/pre-SMA) among younger versus older adolescents. Integrative follow-up analyses showed that EM accounted for this dACC/pre-SMA activation pattern over and above other exposures. Moreover, age-independent results within respective exposure groups revealed that greater magnitude of neglect predicted blunted exclusion-related activity in the parahippocampal gyrus, while EM predicted increased activation to social exclusion in the precuneus/posterior cingulate cortex.

The Pubertal Stress Recalibration Hypothesis: Potential Neural and Behavioral Consequences

Recent research has suggested that the pubertal period provides an opportunity for recalibrating the stress-responsive systems in youth whose responses to stress have been altered by early adversity. Such recalibration may have cascading effects that affect brain and behavioral development. In this article, we consider a large, cross-species literature to demonstrate the potential importance of pubertal stress recalibration for understanding the development of psychopathology following early deprivation by caregivers. We review the evidence for recalibration of the hypothalamic-pituitary-adrenal axis in humans, examine research on rodents that has established mechanisms through which stress hormones affect brain structure and function, and summarize the literature on human neuroimaging to assess how these mechanisms may translate into changes in human behavior. Finally, we suggest ideas for elucidating the consequences of pubertal stress recalibration that will improve our understanding of adaptive and maladaptive adolescent behavior following early adversity.

Microbiota-immune alterations in adolescents following early life adversity: A proof of concept study

Early adverse care has long-term impacts on physical and mental health. The influence of rearing conditions on the infant's gut microbiota and its relationship with developmental health has become more evident. The microbiome is essential for normal growth and metabolism, and the signaling from the gut to the brain may underlie individual differences in resilience later in life. Microbial diversity and composition were determined using 16S rRNA gene amplicon sequencing in fecal samples from 17 adolescents adopted internationally from orphanages into the United States and 18 adolescents reared in birth families who had similar educational and income levels. Analyses focused on diversity of the microbial community structure and differences in the abundance of specific bacterial taxa. Blood samples were used to immunophenotype the numbers of several T-cell subsets and cytomegalovirus (CMV) seropositivity. Negative binomial regression analysis revealed several operational taxonomic units that were significantly different based on early rearing conditions and CMV seropositivity. There were significant associations between the relative abundance of certain taxa, the percentages of T-cell subsets in circulation, and CMV seropositivity. These findings demonstrate a possible link between the gut microbiota and associations with immune alterations initiated by early life adversity.

Pubertal transition with current life stress and support alters longitudinal diurnal cortisol patterns in adolescents exposed to early life adversity

Current and early life stress (ELS) are associated with diurnal cortisol patterns, which themselves are associated with mental and physical health. The pubertal recalibration hypothesis suggests that the social environment can impact dysregulated cortisol patterns for previously ELS-exposed youth as they transition through puberty. This study examined longitudinal change in cortisol awakening response (CAR) and diurnal slope (DS) across puberty as a function of ELS in infancy, current stress, and social support (N = 290, 7-17 years). The CAR and DS were examined thrice annually with an accelerated longitudinal design with nurse-assessed puberty to assess associations between diurnal cortisol and pubertal recalibration with ELS and the current social environment. Exposure to ELS was associated with less steep DS but not changes in CAR, and no evidence of pubertal calibration was found. The DS became less steep for youth in later pubertal stages and as youth progressed through puberty. The CAR was steeper for youth in later pubertal stages. Across the cohort, current life stress and support were associated with changes in the DS and the CAR through the pubertal transition. The pubertal stage and the peripubertal and pubertal social environment may have important implications for adrenocortical functioning with or without exposure to ELS.

Is early life adversity a trigger towards inflammageing?

There are many 'faces' of early life adversity (ELA), such as childhood trauma, institutionalisation, abuse or exposure to environmental toxins. These have been implicated in the onset and severity of a wide range of chronic non-communicable diseases later in life. The later-life disease risk has a well-established immunological component. This raises the question as to whether accelerated immune-ageing mechanistically links early-life adversity to the lifelong health trajectory resulting in either 'poor' or 'healthy' ageing. Here we examine observational and mechanistic studies of ELA and inflammageing, highlighting common and distinct features in these two life stages. Many biological processes appear in common including reduction in telomere length, increased immunosenescence, metabolic distortions and chronic (viral) infections. We propose that ELA shapes the developing immune, endocrine and nervous system in a non-reversible way, creating a distinct phenotype with accelerated immunosenescence and systemic inflammation. We conclude that ELA might act as an accelerator for inflammageing and age-related diseases. Furthermore, we now have the tools and cohorts to be able to dissect the interaction between ELA and later life phenotype. This should, in the near future, allow us to identify the ecological and mechanistic processes that are involved in 'healthy' or accelerated immune-ageing.

Enhancing diurnal cortisol regulation among young children adopted internationally: A randomized controlled trial of a parenting-based intervention

Children who have been adopted internationally commonly experience institutional care and other forms of adversity prior to adoption that can alter the functioning of the hypothalamic-pituitary-adrenal (HPA) axis. In particular, internationally adopted children tend to have blunted diurnal declines compared to children raised in their birth families. The Attachment and Biobehavioral Catch-Up (ABC) intervention was developed to enhance young children's biological and behavioral regulation by promoting sensitive parenting. The current study used a randomized controlled trial to assess whether ABC improved the diurnal functioning of the HPA axis among 85 children who had been adopted internationally when they were between the ages of 4 and 33 months (M = 16.12). Prior to the intervention, there were no significant differences in diurnal cortisol production between children whose parents were randomly assigned to receive ABC and children whose parents were randomly assigned to receive a control intervention. After the intervention, children whose parents had received the ABC intervention exhibited steeper declines in cortisol levels throughout the day than children whose parents had received the control intervention. These results indicate that the ABC intervention is effective in enhancing a healthy pattern of diurnal HPA axis regulation for young children who have been adopted internationally.

Challenges in researching the immune pathways between early life adversity and psychopathology

Exposure to childhood adversity is a critical risk factor for the development of psychopathology. A growing field of research examines how exposure to childhood adversity is translated into biological risk for psychopathology through alterations in immune system functioning, most notably heightened levels of inflammation biomarkers. Though our knowledge about how childhood adversity can instantiate biological risk for psychopathology is growing, there remain many challenges and gaps in the field to understand how inflammation from childhood adversity contributes to psychopathology. This paper reviews research on the inflammatory outcomes arising from childhood adversity and presents four major challenges that future research must address: (a) the measurement of childhood adversity, (b) the measurement of inflammation, (c) the identification of mediators between childhood adversity and inflammation, and (d) the identification of moderators of inflammatory outcomes following childhood adversity. We discuss synergies and inconsistencies in the literature to summarize the current understanding of the association between childhood adversity, a proinflammatory phenotype, and the biological risk for psychopathology. We discuss the clinical implications of the inflammatory links between childhood adversity and psychopathology, including possibilities for intervention. Finally, this review conclude by delineates future directions for research, including issues of how best to detect, prevent, and understand these “hidden wounds” of childhood adversity.

The persistent associations between early institutional care and diurnal cortisol outcomes among children adopted internationally

Young children in institutional care experience conditions that are incompatible with their needs for attachment relationships. As a result, early institutionalization is expected to have lasting effects on the regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis. The current study tested whether early institutionalization has persistent consequences for diurnal HPA axis outcomes among 130 children who had been adopted internationally between the ages of 6 and 48 months. Daily cortisol samples were collected from children at two time points: shortly after adoption (average of 5.3 months after adoption) and approximately 3 years later (average of 39.2 months after adoption). Shortly after adoption, children who had experienced a long duration of institutional care had lower morning cortisol levels and more blunted declines in cortisol across the day than children who experienced minimal or no institutional care. Three years later, children who had experienced a long duration of institutionalization continued to exhibit low morning cortisol levels and also exhibited low bedtime cortisol levels. Altogether, these results support the idea that early adversity results in the downregulation of the HPA axis and suggest that the effects of institutionalization on HPA axis functioning may persist several years after children are adopted into highly enriched families.

Hidden talents in harsh environments

Although early-life adversity can undermine healthy development, children growing up in harsh environments may develop intact, or even enhanced, skills for solving problems in high-adversity contexts (i.e., “hidden talents”). Here we situate the hidden talents model within a larger interdisciplinary framework. Summarizing theory and research on hidden talents, we propose that stress-adapted skills represent a form of adaptive intelligence that enables individuals to function within the constraints of harsh, unpredictable environments. We discuss the alignment of the hidden talents model with current knowledge about human brain development following early adversity; examine potential applications of this perspective to multiple sectors concerned with youth from harsh environments, including education, social services, and juvenile justice; and compare the hidden talents model with contemporary developmental resilience models. We conclude that the hidden talents approach offers exciting new directions for research on developmental adaptations to childhood adversity, with translational implications for leveraging stress-adapted skills to more effectively tailor education, jobs, and interventions to fit the needs and potentials of individuals from a diverse range of life circumstances. This approach affords a well-rounded view of people who live with adversity that avoids stigma and communicates a novel, distinctive, and strength-based message.

Effects of parenting interventions on child and caregiver cortisol levels: systematic review and meta-analysis

BACKGROUND

Nurturing care, in which children are raised in engaging and safe environments, may reduce child stress and shape hypothalamic-pituitary-adrenal axis functioning. Hence, parent-training programs may impact child cortisol levels, as well as behavioral, social and health outcomes. We conducted a systematic review of the impact of parent-training interventions on children's and caregivers' cortisol levels, and meta-analyzed the results.

METHODS

In January 2020, searches in PubMed, LILACS, ERIC, Web of Science, Scielo, Scopus, PsycNET and POPLINE databases were conducted, and two independent researchers screened the results for eligible studies - randomized trials that assessed the impact of parent-training interventions on child or caregiver cortisol levels. Random effects were used to pool the estimates, separately for children and caregivers, and for children's morning and evening cortisol levels, as well as change across the day.

RESULTS

A total of 27 eligible studies were found. Data from 19 studies were extracted and included in the meta-analyses, with 18 estimates of child cortisol levels and 5 estimates for caregiver cortisol levels. The pooled effect size (standardized mean difference) for the effects of parent training programs on morning child cortisol was 0.01 (95%CI: - 0.14 to 0.16; I2: 47.5%), and for caregivers it was 0.04 (95%CI: - 0.22 to 0.30; I2: 0.0%). Similar null results were observed for child evening cortisol and for the slope between morning and evening child cortisol. No evidence of publication bias was found.

CONCLUSION

Existing evidence shows no effect of parent-training interventions on child or caregiver post-intervention cortisol. Researchers are encouraged to adopt standardized protocols to improve evaluation standards, to test for intervention effects on psychosocial outcomes that are theorized to mediate the effects on biomarkers, and to use additional biomarkers for chronic stress.