General Discussion
3. To examine the role of environmental stress (early) in children’s lives on behavior during a stressful situation and (the development of) HPA-axis functioning, as well
as on the associations between HPA-axis and behavioral functioning up to/at the age of 6 (Specific aims 3.1, 3.2, & 3.3).
All research aims were pursued in the BIBO project (Radboud University). BIBO is an ongoing prospective longitudinal project following a cohort of typically developing
chil-S
Summary
122
dren from middle class families from late pregnancy on. In this dissertation data from the prenatal period and the first 6 postnatal years were used, combining behavioral (ob-servations and questionnaires), psychological (questionnaire), and biological (hormonal) measures. In the remainder of this chapter a summary of the four empirical chapters of the dissertation is provided followed by a general conclusion.
Chapter 2
The goal of this chapter was to examine the associations between 6-year-old children’s cortisol stress responses during an acute stressor and their cortisol circadian rhythm (Aim 1.1). To examine this, data of 149 6-year-old children who participated in a social evaluative stress test (Children’s Reactions to Evaluation Stress Test, CREST; de Weerth, Zijlmans, Mack, & Beijers, 2013a) were used. Cortisol stress responses were determined using six cortisol saliva samples. From these samples two cortisol stress response in-dices were calculated: total stress cortisol and cortisol stress reactivity. To determine children’s cortisol circadian rhythm data on eight cortisol circadian samples collected during two days were used. Total diurnal cortisol and diurnal cortisol decline scores were calculated as indices of the cortisol circadian rhythm. The results showed that higher total diurnal cortisol concentrations and a smaller diurnal cortisol decline were both uniquely associated with higher total stress cortisol concentrations. These associations between the circadian indices and total stress cortisol support that both patterns of cor-tisol production (circadian and stress response corcor-tisol production) may derive from the same underlying mechanism: HPA-axis functioning. However, there was no evidence for an association between the circadian markers and cortisol stress reactivity in response to the social evaluative stress test. The finding that more total diurnal cortisol and less diurnal decline were associated with more total stress cortisol may further be explained by children’s self-regulatory capacities and differences in parenting quality.
Chapter 3
The first goal of this chapter was to examine the longitudinal development of children’s cortisol circadian rhythm from age 1 to 6 (Aim 1.2). The second goal was to examine the associations between maternal prenatal and early postnatal distress and (the longitu-dinal development of) children’s cortisol circadian rhythm from age 1 to 6 (Aim 3.1). To examine this, data of 193 healthy mother-child dyads were used. Maternal distress was assessed prenatally in week 37 of gestation and postnatally at child age 3, 6, 12, 30, and 72 months. Child saliva cortisol samples were collected to determine the cortisol circa-dian rhythm at 12, 30, and 72 months. Total diurnal and diurnal cortisol decline were calculated for each of these three time point as indices of the cortisol circadian rhythm.
Summary
123 The results indicated that the cortisol circadian rhythm showed developmental changes between the ages of 1 and 6 years. Specifically, total diurnal cortisol concentrations de-clined between the ages of 1 and 6 and their day-to-day stability increased between the ages of 30 and 72 months. There was no evidence for developmental change in diurnal cortisol decline or its day-to-day stability. Higher levels of maternal pregnancy-specific stress were associated with higher diurnal cortisol concentrations of the children. Higher levels of postnatal maternal anxiety during the first 6 postnatal months were associat-ed with smaller diurnal cortisol declines and higher levels of postnatal maternal stress during the first 6 postnatal months were associated with larger diurnal cortisol declines in the children from age 1 to 6. No support for interaction effects of maternal distress and time were found. The developmental patterns found suggest that the cortisol circa-dian rhythm shows developmental changes between the age of 1 and 6 years. The as-sociations found between maternal distress and child cortisol markers of HPA-axis func-tioning may be pointing at a programming effect of maternal distress early in the child’s life on the cortisol circadian rhythm of the children between the ages of 1 and 6 years.
Chapter 4
The first goal of this chapter was to examine the associations between maternal prenatal and early postnatal distress and 6-year-old children’s cortisol stress responses and gazing during an acute stressor (Aim 3.2). The second goal was to examine the association be-tween 6-year-old children’s cortisol stress responses and gazing during an acute stressor (Aim 2.1). To examine this, data of 149 6-year-olds who participated in a social evaluative stress test in front of a judge were used. Cortisol stress responses were operational-ized by two cortisol stress response indices based on the six cortisol saliva samples that were collected: total stress cortisol and cortisol stress reactivity. Gazing behavior was operationalized by observations of gazing behavior at the judge during the stress test.
Maternal prenatal and early postnatal distress were also measured. The results showed that less maternal fear of giving birth, higher prenatal maternal evening cortisol con-centrations, and more maternal feelings of anxiety in the first 6 postnatal months of the child’s life, were all uniquely associated with higher total stress cortisol concentrations of the children at age 6. In addition, cortisol stress reactivity and gazing behavior during an acute stressful situation were associated. There was no evidence for an association between total stress cortisol and gazing during the stressor nor for a predictive role of maternal distress on child gazing behavior or cortisol stress reactivity. The associations between maternal distress and child total stress cortisol may suggest that maternal dis-tress early in the child’s life may program children’s later HPA-axis functioning.
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Summary
124 Chapter 5
The first goal of this chapter was to examine the associations between 6-year-old chil-dren’s cortisol stress responses during an acute stressor and their behavioral functioning at school (Aim 2.2). The second goal was to examine the moderating role of current ma-ternal parenting stress on the associations between 6-year-old children’s cortisol stress responses during an acute stressor and their behavioral functioning at school (Aim 3.3).
To examine this, data of 149 6-year-old’s who participated in a social evaluative stress test were used. Saliva cortisol samples were collected six times during the stress test to calculate the cortisol stress response. Teachers’ assessments of children’s internalizing, externalizing, and prosocial behaviors were used to operationalize behavioral function-ing. Maternal reports of parenting stress were also used. There was no evidence of an association between cortisol stress responses and behavioral functioning in the class-room nor of a moderating role of current maternal parenting stress on the link between 6-year-olds’ cortisol stress responses and their behavioral functioning at school. Various explanations for these findings are possible including a potential independence of cor-tisol stress responses and behavior at school and study characteristics, such as teacher reports or contextual factors.
In summary, the studies of this dissertation indicated that total diurnal cortisol concen-trations showed developmental change between the ages of 1 and 6 years, and that indices of the cortisol circadian rhythm at the age of 6 were associated with total stress cortisol concentrations. Moreover, maternal distress early in children’s lives was associ-ated with cortisol indices of their later HPA-axis functioning. Finally, 6-year-old children’s gazing in response to a social stressful situation was associated with cortisol stress re-activity. Together, the results of this dissertation indicated that early childhood is an important developmental period for HPA-axis functioning.