Allostatic Load in Childhood, Adolescence, and Young Adulthood: Are Assumptions of Measurement Invariance Warranted?

OVERVIEW: Allostatic load represents the cumulative toll of chronic mobilization of the body's stress response systems, as indexed by biomarkers. Higher levels of stress and disadvantage predict higher levels of allostatic load, which, in turn, predict poorer physical and mental health outcomes. To maximize the efficacy of prevention efforts, screening for stress- and disadvantage-associated health conditions must occur before middle age-that is, during childhood, adolescence, and young adulthood. However, this requires that models of allostatic load display properties of measurement invariance across age groups. Because most research on allostatic load has featured older adults, it is unclear if these requirements can be met. METHODS: To address this question, we fit a series of exploratory and confirmatory analytic models to data on eight biomarkers using a nationally representative sample of N = 4260 children, adolescents, and young adults drawn from the National Health and Nutrition Examination Survey dataset. RESULTS: Exploratory and confirmatory models indicated that, consistent with allostatic load theory, a unidimensional model was a good fit to the data. However, this model did not display properties of measurement invariance; post-hoc analyses suggested that the biomarkers included in the final confirmatory model were most strongly intercorrelated among young adults and most weakly intercorrelated among adolescents. CONCLUSIONS: These results underscore the importance of testing assumptions about measurement invariance in allostatic load before drawing substantive conclusions about stress, disadvantage, and health by directly comparing levels of allostatic load across different stages of development, while underscoring the need to expand investigations of measurement invariance to samples of longitudinal data.

Context is key: Parasympathetic regulation in the classroom differentially predicts preschoolers' socially competent behaviors.

Research shows that children's early social competence predicts their later academic and interpersonal success. Accordingly, early childhood education programs increasingly aim to evaluate and support children's social skill development. Despite ample theoretical and empirical work demonstrating the role of the parasympathetic nervous system (PNS) in supporting neurophysiological processes that underlie social behaviors, no study has explicitly tested whether the assessment of PNS activity in childhood educational settings provides insight into children's social functioning. The current study addresses this gap by examining the influence of context-specific PNS regulation, assessed via respiratory sinus arrhythmia (RSA), in predicting preschool children's socially competent behavior toward peers in the classroom. Results showed that: (1) RSA withdrawal (e.g., decreases relative to a baseline task) during unstructured classroom activities predicted children's socially competent behaviors during these unstructured activities but not during structured activities, whereas (2) withdrawal during structured classroom activities predicted children's socially competent behaviors during structured activities. These results indicate that PNS activity makes context-specific contributions to children's social behaviors and highlight the importance of assessing neurophysiological regulation in context.

Parasympathetic response to challenge in infancy moderates the effects of sociodemographic risk on academic achievement at school entry.

Exposure to higher levels of sociodemographic risk is associated with lower levels of academic achievement among young children. However, there is variability in the strength of this association, which may be traced to individual differences in physiological processes underlying self-regulation. In the current study, we examined whether the response of the parasympathetic nervous system to challenge, indexed by change in respiratory sinus arrhythmia (RSA), moderated the association between risk and school readiness at 5 years of age in a diverse sample of young children. We found that parasympathetic response to the Still-Face Paradigm moderated the effects of risk on a measure of school readiness, such that there was no association between risk and school readiness among children who exhibited RSA decreases during challenge at 6 months of age, a purported index of self-regulation at this age. For those infants who did not exhibit RSA withdrawal during this challenge, exposure to early cumulative risk was associated with lower scores on achievement assessment. These results speak to the possibility that certain patterns of parasympathetic response can serve as a protective factor for young children growing up in disadvantaged environments.

Observed Peer Competence Moderates Links between Children's Self-Regulation Skills and Academic Performance.

The current study focuses on the relations between observed measures of children's self-regulation and academic achievement, as well as the extent to which observations of children's peer competence in preschool moderates these links. Data were drawn from 102 students (male = 48; M age = 4.82 years, SD age = 0.46 years) enrolled in pre-kindergarten classrooms. A series of linear path models was used to test study hypotheses, and the nature of significant interactions was elucidated by examining simple slopes and regions of significance. Children's self-regulation, but not peer competence, significantly predicted both reading and math performance assessed using the Woodcock Johnson III, ß = .43, p < .001 and ß = .39, p < .001, respectively. Tests of moderation effects revealed that the association between children's poor self-regulation and poor math performance, but not reading performance, ß = -.28, p = .022 and ß = -.11, p = .23, was negated for children with average to high peer competence. These results demonstrate the protective quality of peer competence for academic performance using observational methods collected in preschools.

Longitudinal links between maternal factors and infant cognition: Moderation by infant sleep.

The current study examined the moderating role of infant sleep in the link between maternal factors (i.e., maternal education, depressive symptoms, sleep disturbance) and infant cognition. Data come from 95 African American parent-child dyads. At 3 months of age, infant sleep was objectively measured using videosomnography and actigraphy, from which measures of sleep regulation and consolidation were calculated. Mothers also self-reported their level of education, depressive symptoms, and sleep quality. At 6 months of age, infants completed cognitive assessments, including a measure of general cognitive ability and observed attention behavior. Findings revealed that infant sleep quality interacted with maternal education and sleep disturbances to predict cognition. Specifically, the link between maternal education and infants' attention behavior was significant and positive for infants with better regulated sleep, but not for infants with poorly regulated sleep. Similarly, the link between maternal sleep disturbance and infant cognition depended on infant sleep quality. For infants with poorer sleep consolidation, increased maternal sleep disturbance predicted poorer infant general cognitive ability. For infants with better sleep consolidation, maternal sleep disturbance was positively related to both general cognitive ability and attention behavior. These findings suggest that infant sleep quality moderates the impact of environmental factors on cognitive functioning.

Sociodemographic risk, parenting, and inhibitory control in early childhood: the role of respiratory sinus arrhythmia.

BACKGROUND: Deficits of inhibitory control in early childhood are linked to externalizing behaviors and attention problems. While environmental factors and physiological processes are associated with its etiology, few studies have examined how these factors jointly predict inhibitory control. This study examined whether respiratory sinus arrhythmia (RSA) functioned as a mediator or moderator of both cumulative sociodemographic risk and parenting behaviors on inhibitory control during early childhood. METHODS: The sample included 206 children and their biological mothers. At 24, 30, and 36 months of child age dyads participated in a series of laboratory visits in which sociodemographic, parenting, and baseline RSA (RSAB) data were collected. Inhibitory control was assessed at 36 months using a gift-wrap delay task. RESULTS: A series of structural equation models yielded no evidence that RSAB mediated the relations of risk or parenting and inhibitory control. RSAB moderated the effects of risk, such that high-risk children with low RSAB performed more poorly on tasks of inhibitory control, while high-risk children with high RSAB did not. CONCLUSIONS: These results suggest that higher levels of RSAB may mitigate the influence of environmental risk on the development of inhibitory control early childhood.

Children's Executive Function Attenuate the Link Between Maternal Intrusiveness and Internalizing Behaviors at School Entry.

The goal of this study was to examine the independent and interactive roles of harsh-intrusive maternal behaviors and children's executive function in the development of internalizing behaviors across the first years of school. A diverse sample (58% African American, 42% European American) of 137 children (48% female) was followed from kindergarten (age 5 years) through school entry (ages 6-7 years). At age 5, maternal harsh-intrusive parenting behaviors were rated from a mother-child structured play task, and children completed 3 executive function tasks that measured inhibitory control, working memory, and attention set-shifting. Teachers reported on children's internalizing behaviors at ages 5, 6, and 7. Harsh-intrusive parenting behaviors at age 5 years were positively related to internalizing behaviors in the first years of school, whereas high executive function abilities at age 5 years were related to lower internalizing behaviors in the first years of school. In addition, executive function buffered the association between parenting behaviors and internalizing behaviors such that the link between harsh-intrusive parenting and child internalizing behaviors was evident only among children with low executive function and not among children with high executive function. Interventions that focus on reducing negative parenting behaviors and improving children's executive function may prevent internalizing behaviors from increasing during times of social and academic challenge.

Automated respiratory sinus arrhythmia measurement: Demonstration using executive function assessment.

Respiratory sinus arrhythmia (RSA) is a quantitative metric that reflects autonomic nervous system regulation and provides a physiological marker of attentional engagement that supports cognitive and affective regulatory processes. RSA can be added to executive function (EF) assessments with minimal participant burden because of the commercial availability of lightweight, wearable electrocardiogram (ECG) sensors. However, the inclusion of RSA data in large data collection efforts has been hindered by the time-intensive processing of RSA. In this study we evaluated the performance of an automated RSA-scoring method in the context of an EF study in preschool-aged children. The absolute differences in RSA across both scoring methods were small (mean RSA differences = -0.02-0.10), with little to no evidence of bias for the automated relative to the hand-scoring approach. Moreover, the relative rank-ordering of RSA across both scoring methods was strong (rs = .96-.99). Reliable changes in RSA from baseline to the EF task were highly similar across both scoring methods (96%-100% absolute agreement; Kappa = .83-1.0). On the basis of these findings, the automated RSA algorithm appears to be a suitable substitute for hand-scoring in the context of EF assessment.

Vagal Regulation in Breastfeeding Infants and Their Mothers.

Consistent with the gustatory-vagal hypothesis, vagal stimulation during breastfeeding may contribute to infants' physiological regulatory development independent of caregiving effects. This study examined whether breastfeeding predicted 6-month-old infants' (N = 151) and their mothers' vagal regulation during the face-to-face still-face (FFSF). Although breastfed and nonbreastfed infants showed expected vagal withdrawal during the Still-Face episode, only breastfed infants showed continued withdrawal during the reunion episode, suggesting greater physiological mobilization to repair the interaction. Breastfeeding mothers showed higher vagal tone than nonbreastfeeding mothers at baseline, suggesting greater capacity for regulation, and throughout the FFSF, suggesting calmer states. Breastfeeding effects were independent of maternal sensitivity. Findings suggest that infants' and mothers' physiological regulation may be shaped by breastfeeding independently of associated social factors.

Infant respiratory sinus arrhythmia and maternal depressive symptoms predict toddler sleep problems.

This study examined the direct and interactive effects of infants' respiratory sinus arrhythmia (RSA) and maternal depressive symptoms (MDS) during the first 6 months of life in the prediction of children's sleep problems at age 18 months. Participants included 156 children and their mothers who were followed from 3 to 18 months of age. At ages 3 and 6 months, infants' cardiac activity was recorded at rest and during the still-face paradigm, a mother-child social challenge task, and estimates of infant baseline RSA (RSAB) and RSA withdrawal (RSAW) were calculated. Mothers reported about their depressive symptoms at 3, 6, and 18 months, and about infants' sleep problems at age 18 months. Less RSAW and higher levels of MDS predicted more sleep problems at age 18 months. Additionally, RSAB moderated the link between MDS and children's sleep problems such that MDS were related to more sleep problems only for infants with high levels of RSAB. Results illustrate the importance of RSA as both a direct predictor and a moderator of maternal influences in the prediction of early sleep problems.

The Interaction Between Child Respiratory Sinus Arrhythmia and Early Sensitive Parenting in the Prediction of Children's Executive Functions.

This study investigated the interaction between children's parasympathetic functioning and maternal sensitive parenting behaviors during infancy and toddlerhood in the prediction of children's executive functions (EF) at the age of 5 years. Participants included 137 children and their mothers who were followed from the age of 3 months to 5 years. Children's cardiac activity was recorded at rest at multiple times from ages 3 to 36 months, and estimates of respiratory sinus arrhythmia (RSA; a measure of parasympathetic functioning) were calculated. Sensitive parenting was assessed during a mother-child play task at ages 6, 12, 24, and 36 months, and 5 years. Children completed age appropriate EF tasks at the age of 5 years. The link between sensitive parenting during toddlerhood (ages 24 and 36 months) and children's later EF was moderated by children's RSA such that this positive link was evident only among children who had low levels of baseline RSA, and not among those who had high levels of baseline RSA. These findings were obtained while controlling for concurrent sensitive parenting and maternal and child verbal abilities. Results from this study provide evidence for the significant role of biopsychosocial processes in early childhood in the development of EF.

Early identification of ADHD risk via infant temperament and emotion regulation: a pilot study.

BACKGROUND: Attention deficit hyperactivity disorder (ADHD) is theorized to have temperamental precursors early in life. These are difficult to identify because many core features of ADHD, such as breakdowns in executive function and self-control, involve psychological and neural systems that are too immature to reliably show dysfunction in early life. ADHD also involves emotional dysregulation, and these temperamental features appear earlier as well. Here, we report a first attempt to utilize indices of emotional regulation to identify ADHD-related liability in infancy. METHODS: Fifty women were recruited in the 2nd trimester of pregnancy, with overselection for high parental ADHD symptoms. Measures of maternal body mass index, nutrition, substance use, stress, and mood were examined during pregnancy as potential confounds. Offspring were evaluated at 6 months of age using LABTAB procedures designed to elicit fear, anger, and regulatory behavior. Mothers completed the Infant Behavior Questionnaire about their child's temperament. RESULTS: After control for associated covariates, including maternal depression and prenatal stress, family history of ADHD was associated with measures of anger/irritability, including infant negative vocalizations during the arm restraint task (p = .004), and maternal ratings of infant distress to limitations (p = .036). In the regulation domain, familial ADHD was associated with less parent-oriented attention seeking during the still face procedure (p < .001), but this was not echoed in the maternal ratings of recovery from distress. CONCLUSIONS: Affective response at 6 months of age may identify infants with familial history of ADHD, providing an early indicator of ADHD liability. These preliminary results provide a foundation for further studies and will be amplified by enlarging this cohort and following participants longitudinally to evaluate ADHD outcomes.

Parenting behaviors and vagal tone at six months predict attachment disorganization at twelve months.

The authors investigated the relationships among parenting behaviors, infant vagal tone, and subsequent attachment classification. Vagal tone was assessed among 6-month olds (n = 95) during the still-face paradigm (SFP) via respiratory sinus arrhythmia (RSA), while attachment security and disorganization were measured at 12 months during the strange situation procedure (SSP). Infants demonstrating higher levels of RSA during the normal interaction and reunion episodes of the SFP whose mothers were also rated as negative-intrusive exhibited higher levels of attachment disorganization at 12 months, while infants with lower RSA and mothers who were negative-intrusive did not exhibit higher levels of disorganization. These results suggest that high levels of RSA may not be adaptive within the context of negative-intrusive parenting.

Maternal prenatal lead levels and neonatal brain volumes: Testing moderations by maternal depressive symptoms and family income.

There is considerable evidence that prenatal lead exposure is detrimental to child cognitive and socio-emotional development. Further evidence suggests that the effects of prenatal lead on developmental outcomes may be conditional upon exposure to social stressors, such as maternal depression and low socioeconomic status. However, no studies have examined associations between these co-occurring stressors during pregnancy and neonatal brain volumes. Leveraging a sample of 101 mother-infant dyads followed beginning in mid-pregnancy, we examined the main effects of prenatal urinary lead levels on neonatal lateralized brain volumes (left and right hippocampus, amygdala, cerebellum, frontal lobes) and total gray matter. We additionally tested for moderations between lead and depressive symptoms and between lead and family income relative to the federal poverty level (FPL) on the same neurodevelopmental outcomes. Analyses of main effects indicated that prenatal lead was significantly (ps < 0.05) associated with reduced right and left amygdala volumes (ßs = -0.23- -0.20). The testing and probing of cross-product interaction terms using simple slopes indicated that the negative effect of lead on the left amygdala was conditional upon mothers having low depressive symptoms or high income relative to the FPL. We interpret the results in the context of trajectories of prenatal and postnatal brain development and susceptibility to low levels of prenatal lead in the context of other social stressors.

Sleep, Health Outcomes and Body Weight (SHOW) study: a measurement burst design study on sleep and risk factors for obesity in black emerging adults in North Carolina, USA.

INTRODUCTION: Black emerging adults (18-28 years) have the highest risk of short sleep duration and obesity. This increased risk may be partly explained by greater stress levels, which may result from race-related stress (racial discrimination and heightened race-related vigilance) or living in more disadvantaged home and neighbourhood environments. Insufficient sleep may also impact obesity risk via several weight-related mechanisms including energy balance, appetite and food reward, cortisol profiles and hydration status. This paper describes the rationale, design and methods for the Sleep, Health Outcomes and Body Weight (SHOW) study. This study aims to prospectively assess the effects of sleep, race-related stress and home/neighbourhood environments on weight-related mechanisms and obesity markers (body weight, waist circumference and fat mass) in 150 black emerging adults. METHODS AND ANALYSIS: The SHOW study follows a measurement burst design that includes 3, 7-day data collection bursts (baseline, 6-month and 12-month follow-ups). Sleep is measured with three methods: sleep diary, actigraphy and polysomnography. Energy balance over 7 days is based on resting and postprandial energy expenditure measured via indirect calorimetry, physical activity via accelerometry and self-reported and ad libitum energy intake methods. Self-reported methods and blood biomarkers assess fasting and postprandial appetite profiles and a behavioural-choice task measures food reward. Cortisol awakening response and diurnal cortisol profiles over 3 days are assessed via saliva samples and chronic cortisol exposure via a hair sample. Hydration markers are assessed with 24-hour urine collection over 3 days and fasting blood biomarkers. Race-related stress is self-reported over 7 days. Home and neighbourhood environments (via the Windshield Survey) is observer assessed. ETHICS AND DISSEMINATION: Ethics approval was granted by the University of North Carolina at Greensboro's Institutional Review Board. Study findings will be disseminated through peer-reviewed publications, presentations at scientific meetings and reports, briefs/infographics for lay and community audiences.

Observed parenting behaviors interact with a polymorphism of the brain-derived neurotrophic factor gene to predict the emergence of oppositional defiant and callous-unemotional behaviors at age 3 years.

Using the Durham Child Health and Development Study, this study (N = 171) tested whether observed parenting behaviors in infancy (6 and 12 months) and toddlerhood/preschool (24 and 36 months) interacted with a child polymorphism of the brain-derived neurotrophic factor gene to predict oppositional defiant disorder (ODD) and callous-unemotional (CU) behaviors at age 3 years. Child genotype interacted with observed harsh and intrusive (but not sensitive) parenting to predict ODD and CU behaviors. Harsh-intrusive parenting was more strongly associated with ODD and CU for children with a methionine allele of the brain-derived neurotrophic factor gene. CU behaviors were uniquely predicted by harsh-intrusive parenting in infancy, whereas ODD behaviors were predicted by harsh-intrusive parenting in both infancy and toddlerhood/preschool. The results are discussed from the perspective of the contributions of caregiving behaviors as contributing to distinct aspects of early onset disruptive behavior.

Vagal Flexibility Moderates the Links between Observed Sensitive Caregiving in Infancy and Externalizing Behavior Problems in Middle Childhood.

This study explored how patterns of physiological stress reactivity underpin individual differences in sensitivity to early rearing experiences and childhood risk for psychopathology. To examine individual differences in parasympathetic functioning, past research has largely relied on static measures of stress reactivity (i.e., residual and change scores) in infancy which may not adequately capture the dynamic nature of regulation across contexts. Using data from a prospective longitudinal study of 206 children (56% African Americans) and their families, this study addressed these gaps by employing the latent basis growth curve model to characterize the dynamic, non-linear patterns of change in infants' respiratory sinus arrhythmia (i.e., vagal flexibility) across the Face-to-Face Still-Face Paradigm. Furthermore, it investigated whether and how infants' vagal flexibility moderates the links between sensitive parenting, observed during a free play task when children were 6 months of age, and parent-report of children's externalizing problems at 7 years of age. Results of the structural equation models revealed that infants' vagal flexibility moderates the predictive relations between sensitive parenting in infancy and children's later externalizing problems. Simple slope analyses revealed that low vagal flexibility, characterized by less suppression and flatter recovery patterns, exacerbated risk for externalizing psychopathology in the context of insensitive parenting. Children with low vagal flexibility also benefited most from sensitive parenting, as indicated by the lower number of externalizing problems. Findings are interpreted in the light of the biological sensitivity to context model and provide evidence for vagal flexibility as a biomarker of individual's sensitivity to early rearing contexts.

Evocative gene-parenting correlations and academic performance at first grade: an exploratory study.

Academic performance during the first years of school lays the groundwork for subsequent trajectories of academic success throughout childhood and adolescence. The current study tests a model according to which a gene-parenting correlation in the first 3 years of life is associated with subsequent psychosocial adjustment and then academic performance in the first grade (as indicated by teachers' assessment of academic behavior and two subscales of the Woodcock-Johnson Test of Achievement, Third Edition). Drawing on multiple waves of data from the Durham Child Health and Development Study, we find that risk alleles for dopamine receptor genes (dopamine receptor D4 for girls, dopamine receptor D2 for boys) are associated with less sensitive parenting. For girls, parenting mediates the link between dopamine receptor D4 and all academic outcomes. There is some indication that parenting also influences girls' withdrawn behavior in the classroom, which in turn influences teachers' assessments of academic performance. For boys, some evidence suggests that parenting is associated with emotion regulation, which is associated with teachers' assessments of academic behavior and both subscales of the Woodcock-Johnson. Replications of this exploratory study are necessary, but these findings provide a first step in understanding how evocative correlations in the home may predict indicators of psychosocial adjustment that in turn influence performance and achievement at school.

Developmental trajectories of toddler sleep problems: can a person-centered approach help identify children at risk?

STUDY OBJECTIVES: Previous research examining toddler sleep problems has relied almost exclusively on variable-centered statistical approaches to analyze these data, which provide helpful information about the development of the average child. The current study examined whether person-centered trajectory analysis, a statistical technique that can identify subgroups of children who differ in their initial level and/or trajectory of sleep problems, has the potential to inform our understanding of toddler sleep problems and their development. METHODS: Families (N = 185) were assessed at 12, 24, 30, and 36 months of child age. Latent class growth analysis was used to test for subgroups that differed in their 24-36 month sleep problems. Subgroups were compared on child 36-month externalizing, internalizing, and total problem behaviors, and on 12 month maternal mental health, inter-parental conflict, and maternal parenting behaviors. RESULTS: Results support a four-class solution, with "low, stable," "low, increasing," "high, increasing," and "high decreasing" classes. The classes whose sleep problems persisted or worsened over time had worse behavioral problems than those whose symptoms improved or remained stably low. Additionally, 12 month maternal depression and global symptom severity, intimate partner violence, and maternal harsh-intrusive parenting behaviors discriminated between the classes that had similar levels of 24 month sleep disturbance but who had diverging trajectories over time. CONCLUSIONS: This statistical approach appears to have the potential to increase understanding of sleep problem trajectories in the early years of life. Maternal mental health, intimate partner violence, and parenting behaviors may be clinically useful markers of risk for the persistence or development of toddler sleep problems.

Testing a cascade model linking prenatal inflammation to child executive function.

Inflammation during pregnancy is beginning to be understood as a risk factor predicting poor infant health and neurodevelopmental outcomes. The long-term sequelae associated with exposure to prenatal inflammation are less well established. The current study examined associations between maternal inflammation during pregnancy, markers of infant neurodevelopment (general cognitive ability, negative affect, and sleep quality), and preschool executive function (EF) in a longitudinal sample of 40 African American mother-infant dyads. Mothers completed a blood draw in the third trimester of pregnancy to measure plasma levels of C-reactive protein (CRP) and pro-inflammatory cytokines (e.g., interleukin 6 [IL-6], tumor necrosis factor-alpha [TNF-α]). When infants were 6 months of age, we assessed general cognitive ability via the Bayley-III, negative affect via the Still-Face Paradigm, and sleep quality via actigraphy monitoring. When children were 4 years of age, we assessed their EF ability using four tasks from the EF Touch battery. Elevated levels of maternal CRP, IL-6, and TNF-α were associated with poorer infant general cognitive ability. Although there were no direct effects of prenatal inflammation on preschool EF, we observed an indirect relationship between IL-6 and preschool EF ability via infant general cognitive ability. Our findings suggest that prenatal inflammation may have long-lasting, cascading implications for child neurodevelopment. Implications of these findings for health disparities in women and children of color are discussed.