Theory suggests that early experiences may calibrate the threshold activity of the hypothalamus-pituitary-adrenal axis in childhood. Particularly challenging or particularly supportive environments are posited to manifest in heightened physiological sensitivity to context. Using longitudinal data from the Family Life Project (N = 1,292), we tested whether links between maternal sensitivity and hypothalamus-pituitary-adrenal axis activity aligned with these predictions. Specifically, we tested whether the magnitude of the within-person relation between maternal sensitivity and childrens cortisol levels, a proxy for physiological sensitivity to context, was especially pronounced for children who typically experienced particularly low or high levels of maternal sensitivity over time. Our results were consistent with these hypotheses. Between children, lower levels of mean maternal sensitivity (7-24 months) were associated with higher mean cortisol levels across this period (measured as a basal sample collected at each visit). However, the magnitude and direction of the within-person relation was contingent on childrens average levels of maternal sensitivity over time. Increases in maternal sensitivity were associated with contemporaneous cortisol decreases for children with typically low-sensitive mothers, whereas sensitivity increases were associated with cortisol increases for children with typically high-sensitive mothers. No within-child effects were evident at moderate levels of maternal sensitivity.

BACKGROUND: Approximately one third of children who meet criteria for conduct problems (CP) are also characterized by elevated callous-unemotional (CU) traits. This subgroup is at elevated risk for more pervasive and extreme levels of later antisocial behavior and has been characterized by a fearlessness temperament and blunted stress psychophysiology at older ages. The objective of this study was to examine group differences in fear reactivity and stress psychophysiology in infancy among children classified as having CP with CU (CP + CU), CP without CU (CP only), or no CP in later childhood. METHODS: A birth cohort study (n = 1,292) was followed longitudinally from birth through first grade. Behavioral fear, baseline heart period (HP) and respiratory sinus arrhythmia (RSA), and pretask, 20-min posttask, and 40-min posttask salivary cortisol were assessed at 6 and 15 months of age around a fear challenge task. CP and CU were assessed by maternal report at first grade and children were classified into CP and CU groups if they scored in the upper 10(th) percentile of these ratings. RESULTS: No group differences were observed in children at 6 months of age. However, at 15 months of age children with later CP + CU displayed greater high-intensity fear behavior, higher pretask and overall cortisol levels, and lower levels of HP and RSA compared to children with CP only and children with no CP. CONCLUSIONS: The discrepancy between the biobehavioral correlates of conduct problems with callous-unemotional traits in infancy and those reported from studies of older children and adults suggests that the etiology of this behavioral phenotype may be more complex than a simple genetic maturation model.

Introduction

Infants and young children may be at an increased risk for second- and thirdhand exposure to tobacco smoke because of increased respiration rate and exposure to surface residue. However, relatively fewer studies have examined biomarkers of exposure (cotinine) in children under age 4 years. This study examines the magnitude and chronicity of exposure across early childhood among children from low-income families in order to better characterize contextual risk factors associated with exposure.

Methods

A total of 1292 families were recruited in six nonurban counties of Pennsylvania and North Carolina. Cotinine was assayed from infant saliva at 6, 15, 24, and 48 months of age (N = 1218), and categorized as low (≤0.45 ng/mL), moderate (0.46-12 ng/mL), or high (≥12 ng/mL) at each time point. Categories were highly correlated across time. Latent class analysis was used to summarize patterns of exposure categories across time.

Results

Magnitude of exposure in this sample was high, with approximately 12% of infants registering cotinine values at least 12 ng/mL, consistent with active smoking in adults. Greater exposure was associated with lower income, less education, more residential instability, and more instability in adult occupants in the home, whereas time spent in center-based day care was associated with lower exposure.

Conclusions

Young children from low-income, nonurban communities appear to bear a higher burden of secondhand smoke exposure than previous studies have reported. Results contribute to understanding populations at greater risk, as well as specific, potentially malleable, environmental factors that may be examined as direct contributors to exposure.

Implications

Results suggest that infants from low-income, nonurban families have higher risk for environmental smoke exposure than data from nationally representative samples. Predictors of exposure offer insights into specific factors that may be targeted for risk reduction efforts, specifically conditions of children's physical space. In addition to considering the increases in risk when an adult smoker lives in a child's home, families should also attend to the possible risk embedded within the home itself, such as residual smoke from previous occupants. For high-risk children, day care appears to mitigate the magnitude of exposure by providing extended time in a smoke-free environment.

INTRODUCTION: Infants and young children may be at an increased risk for second- and thirdhand exposure to tobacco smoke because of increased respiration rate and exposure to surface residue. However, relatively fewer studies have examined biomarkers of exposure (cotinine) in children under age 4 years. This study examines the magnitude and chronicity of exposure across early childhood among children from low-income families in order to better characterize contextual risk factors associated with exposure. METHODS: A total of 1292 families were recruited in six nonurban counties of Pennsylvania and North Carolina. Cotinine was assayed from infant saliva at 6, 15, 24, and 48 months of age (N = 1218), and categorized as low (≤0.45 ng/mL), moderate (0.46-12 ng/mL), or high (≥12 ng/mL) at each time point. Categories were highly correlated across time. Latent class analysis was used to summarize patterns of exposure categories across time. RESULTS: Magnitude of exposure in this sample was high, with approximately 12% of infants registering cotinine values at least 12 ng/mL, consistent with active smoking in adults. Greater exposure was associated with lower income, less education, more residential instability, and more instability in adult occupants in the home, whereas time spent in center-based day care was associated with lower exposure. CONCLUSIONS: Young children from low-income, nonurban communities appear to bear a higher burden of secondhand smoke exposure than previous studies have reported. Results contribute to understanding populations at greater risk, as well as specific, potentially malleable, environmental factors that may be examined as direct contributors to exposure. IMPLICATIONS: Results suggest that infants from low-income, nonurban families have higher risk for environmental smoke exposure than data from nationally representative samples. Predictors of exposure offer insights into specific factors that may be targeted for risk reduction efforts, specifically conditions of childrens physical space. In addition to considering the increases in risk when an adult smoker lives in a childs home, families should also attend to the possible risk embedded within the home itself, such as residual smoke from previous occupants. For high-risk children, day care appears to mitigate the magnitude of exposure by providing extended time in a smoke-free environment.

Theory suggests that early experiences may calibrate the "threshold activity" of the hypothalamus-pituitary-adrenal axis in childhood. Particularly challenging or particularly supportive environments are posited to manifest in heightened physiological sensitivity to context. Using longitudinal data from the Family Life Project (N = 1,292), we tested whether links between maternal sensitivity and hypothalamus-pituitary-adrenal axis activity aligned with these predictions. Specifically, we tested whether the magnitude of the within-person relation between maternal sensitivity and children's cortisol levels, a proxy for physiological sensitivity to context, was especially pronounced for children who typically experienced particularly low or high levels of maternal sensitivity over time. Our results were consistent with these hypotheses. Between children, lower levels of mean maternal sensitivity (7-24 months) were associated with higher mean cortisol levels across this period (measured as a basal sample collected at each visit). However, the magnitude and direction of the within-person relation was contingent on children's average levels of maternal sensitivity over time. Increases in maternal sensitivity were associated with contemporaneous cortisol decreases for children with typically low-sensitive mothers, whereas sensitivity increases were associated with cortisol increases for children with typically high-sensitive mothers. No within-child effects were evident at moderate levels of maternal sensitivity.

Exposure to toxic heavy metals has been associated with the development of attention-deficit/hyperactivity disorder (ADHD). However, fewer studies have examined the associations between abnormal levels of essential trace metals and ADHD, and none have done so using saliva. We investigated whether salivary metals were associated with ADHD in adolescents aged 12 from the Family Life Project (FLP) using a nested case-control study design that included 110 adolescents who met diagnostic criteria for inattentive (ADHD-I), hyperactive-impulsive (ADHD-H), or combined type ADHD (ADHD-C) (cases) and 173 children who did not (controls). We used inductively coupled plasma optical emission spectrophotometry to measure chromium, copper, manganese, and zinc in saliva samples. We employed logistic regression models to examine associations between quartile levels of individual metals and ADHD outcomes by subtype. Salivary copper levels were significantly associated with increased odds of any ADHD diagnosis (OR = 3.31, 95% CI: 1.08-10.12; p = 0.04) and with increased odds of ADHD-C diagnosis (OR = 8.44, 95% CI: 1.58-45.12; p = 0.01). Salivary zinc levels were significantly associated with increased odds of ADHD-C diagnosis (OR = 4.06, 95% CI: 1.21-13.69; p = 0.02). Salivary manganese levels were also significantly associated with increased odds of ADHD-C diagnosis (OR = 5.43, 95% CI: 1.08-27.27, p = 0.04). This is the first study using saliva to assess metal exposure and provide a potential link between salivary levels of copper, manganese, and zinc and ADHD diagnoses in adolescents. Public health interventions focused on metal exposures might reduce ADHD incidence in low-income, minority communities.

Background

Approximately one third of children who meet criteria for conduct problems (CP) are also characterized by elevated callous-unemotional (CU) traits. This subgroup is at elevated risk for more pervasive and extreme levels of later antisocial behavior and has been characterized by a fearlessness temperament and blunted stress psychophysiology at older ages. The objective of this study was to examine group differences in fear reactivity and stress psychophysiology in infancy among children classified as having CP with CU (CP + CU), CP without CU (CP only), or no CP in later childhood.

Methods

A birth cohort study (n = 1,292) was followed longitudinally from birth through first grade. Behavioral fear, baseline heart period (HP) and respiratory sinus arrhythmia (RSA), and pretask, 20-min posttask, and 40-min posttask salivary cortisol were assessed at 6 and 15 months of age around a fear challenge task. CP and CU were assessed by maternal report at first grade and children were classified into CP and CU groups if they scored in the upper 10(th) percentile of these ratings.

Results

No group differences were observed in children at 6 months of age. However, at 15 months of age children with later CP + CU displayed greater high-intensity fear behavior, higher pretask and overall cortisol levels, and lower levels of HP and RSA compared to children with CP only and children with no CP.

Conclusions

The discrepancy between the biobehavioral correlates of conduct problems with callous-unemotional traits in infancy and those reported from studies of older children and adults suggests that the etiology of this behavioral phenotype may be more complex than a simple genetic maturation model.