New research
A Discordant Monozygotic Twin Design Shows Blunted Cortisol Reactivity Among Bullied Children

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Objective

Childhood adverse experiences are known to engender persistent changes in stress-related systems and brain structures involved in mood, cognition, and behavior in animal models. Uncertainty remains about the causal effect of early stressful experiences on physiological response to stress in human beings, as the impact of these experiences has rarely been investigated while controlling for both genetic and shared environmental influences.

Method

We tested whether bullying victimization, a repeated adverse experience in childhood, influences cortisol responses to a psychosocial stress test (PST) using a discordant monozygotic (MZ) twin design. Thirty pairs (43.3% males) of 12-year-old MZ twins discordant for bullying victimization were identified in the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative 1994–1995 cohort of families with twins.

Results

Bullied and nonbullied MZ twins showed distinct patterns of cortisol secretion after the PST. Specifically, bullied twins exhibited a blunted cortisol response compared with their nonbullied MZ co-twins, who showed the expected increase. This difference in cortisol response to stress could not be attributed to children's genetic makeup, their familial environments, pre-existing and concomitant individual factors, or the perception of stress and emotional response to the PST.

Conclusion

Results from this natural experiment provide support for a causal effect of adverse childhood experiences on the neuroendocrine response to stress.

Section snippets

Sample

Participants were recruited from the E-Risk Longitudinal Twin Study, which tracks the development of a nationally representative birth cohort of 2,232 British children.21 The sample was drawn from a larger birth register of twins born in England and Wales in 1994–1995. The E-Risk sample was constructed in 1999–2000, when 1,116 families with same-gender 5-year-old twins (93% of those eligible) participated in home-visit assessments. Follow-up home visits were conducted when the children were

Results

Repeated-measures ANOVA showed distinct patterns of cortisol secretion over time between bullied and nonbullied MZ twins (time × bullying: F2.2,122.9 = 3.82, P = .02) (Figure 1). More specifically, both groups had similar levels of cortisol prior to the PST (F1,56 = 1.26, P = .27), but distinct patterns of secretion emerged subsequently as a function of time (+15 minutes vs. later; Helmert time × bullying (within-subjects) contrast: F1,56 = 6.18, P = .02). We explored further this interaction

Discussion

This study provides evidence for a causal effect of early-life stress on cortisol reactivity in human beings. Our psychosocial stress test elicited a cortisol response in nonbullied children compared with a blunted response in bullied children. Cortisol differences between bullied and nonbullied children were observed in a stringent discordant MZ twin design, in which distinct cortisol responses to stress could not be attributable to either the children's genetic makeup or their shared familial

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    The E-Risk Study is funded by the Medical Research Council (MRC; G9806489). Additional support was provided by the British Academy, the Jacobs Foundation, the Economic and Social Research Council (ESRC; RES-177-25-0013), the Nuffield Foundation, and the National Institute of Child Health and Human Development (HD061298). Additional support was provided by the Canadian Institutes of Health Research (I.O.M.), the National Alliance for Research on Schizophrenia and Depression Young Investigator Award (A.D.), the ESRC (L.B.), the MRC (S.S.), a Career Scientist Award from the UK Department of Health (L.A.), a Royal Society Wolfson Research Merit Award (A.C.), the Lady Davis Fellowship of the Hebrew University, and the Caselberg Trust (A.C. and T.E.M.).

    Disclosure: Drs. Ouellet-Morin, Danese, Bowes, Pariante, Papadopoulos, Caspi, Moffitt, and Arseneault, and Ms. Shakoor, and Mr. Ambler report no biomedical financial interests or potential conflicts of interest.

    This article is discussed in an editorial by Dr. Guilherme Polanczyk on page 538.

    Supplemental material cited in this article is available online.

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