Childhood Trauma and Psychosis in a Prospective Cohort Study: Cause, Effect, and Directionality

Participants completed a self-report survey, administered in the classroom, in which they were asked about a number of childhood trauma exposures, including physical abuse and bullying. To assess physical abuse, participants were asked at baseline if they had been physically attacked in the past 12 months (“Have you, during the past 12 months, been physically attacked?” Answer: yes or no). They were then asked if the attack had been perpetrated by a parent, other relative, schoolmate, other acquaintance, or an unknown individual. A series of yes-or-no questions were used to assess bullying at baseline (“In the past 12 months, have others often spread rumors about you? Teased you? Deliberately left you out of activities? Taken money, property, or food from you? Called you names? Made fun of how you look or talk?”). These questions were used to create a binomial variable of bullying, with an answer of yes to any of the six questions being categorized as bullying. These questions were also used to create a measure of bullying severity: a continuous variable scored 0 to 6, indicating the number of questions endorsed. These measures were repeated at the 3-month and 12-month follow-ups, with the wording adjusted to inquire about the time interval since the previous assessment.

Psychotic experiences were assessed using an item validated as part of the Adolescent Psychotic Symptom Screener (29). We previously showed that the question “Have you ever heard voices or sounds that no one else can hear?” demonstrates excellent positive and negative predictive value for phenomena that, on subsequent interview, are clinically verifiable as psychotic in nature (29). In a community survey of adolescents, this item not only detected young people with auditory hallucinations (compared with clinical-interview-verified auditory hallucinations; positive predictive value=71%, negative predictive value=90%), but psychotic symptoms in general (hallucinations and delusions) (positive predictive value=100%, negative predictive value=88%). Therefore, we used this validated question specifically to assess for psychotic experiences in our sample at baseline and at 3 and 12 months.

The study received ethical approval from the European Commission as a precondition of funding approval for the project. Ethical approval was also obtained in each participating country, including from the clinical research ethics committee of the Cork Teaching Hospitals in Ireland. An independent ethical adviser supervises the implementation of the ongoing project to ensure maximum protection of vulnerable individuals. Participants were informed that all answers were confidential (including a report of psychotic experiences) with the exception of some answers to questions relating to suicidal behavior. Specifically, a response of sometimes, often, very often, or always to the question “Have you ever reached the point where you seriously considered taking your life, or perhaps made plans how you would go about doing it?” or a response of yes to the question “Have you ever made an attempt to take your own life?” were considered emergency cases (27). Pupils identified as emergency cases were immediately referred for clinical evaluation to health care services.

All analyses were performed using Stata, version 11.1 (StataCorp, College Station, Tex.). Analyses were controlled for sex.

Next, we looked at traumatic experiences reported at baseline and psychotic experiences reported at 3 months and at 12 months. Physical assault reported at baseline predicted psychotic experiences at 3 and 12 months, even after adjusting for psychotic experiences at baseline (Table 2). Similarly, bullying reported at baseline predicted psychotic experiences at 3 and 12 months, even after adjusting for psychotic experiences at baseline. The odds of reporting psychotic experiences increased in a dose-response fashion with increasing severity of bullying, as assessed by the number of bullying questions endorsed at each of the three assessments (Table 3).

A total of 111 individuals reported a 12-month history of physical assault at baseline (odds ratio for psychotic experiences, 4.02, 95% CI=2.30–7.05, p<0.001). Of these individuals, 37% also reported at least one physical assault between baseline and the 3-month follow-up. Individuals whose experience of physical assault did not reoccur between baseline and the 3-month follow-up had a lower risk of psychotic symptoms at 3 months compared with those whose experience of physical assault continued (odds ratio=0.17, 95% CI=0.04–0.71, p=0.015) (Figure 1). Similarly, individuals whose experience of physical assault did not reoccur between the 3-month and 12-month follow-ups had a lower risk of psychotic symptoms at 12 months compared with those whose experience of physical assault continued (odds ratio=0.16, 95% CI=0.05–0.53, p<0.003).

Next, we looked at whether cessation of bullying predicted cessation of psychotic experiences. A total of 409 individuals reported a 12-month history of bullying at baseline (odds ratio for psychotic experiences, 3.05, 95% CI=1.85–5.02, p<0.001). Of these individuals, 56% also reported bullying between baseline and the 3-month follow-up. Individuals whose experience of bullying did not reoccur between baseline and the 3-month follow-up had a lower risk of psychotic experiences at 3 months compared with those whose experience of bullying continued (odds ratio=0.28, 95% CI=0.12–0.65, p=0.003). Similarly, individuals whose experience of bullying did not reoccur between the 3-month and 12-month follow-ups had a significantly lower risk of psychotic experiences at 12 months compared with individuals whose experience of bullying continued (odds ratio=0.35, 95% CI=0.15–0.84, p=0.019).

Psychotic experiences reported at baseline predicted physical assault at 3 months and at 12 months, even after adjusting for baseline reports of physical assault (3-month odds ratio=7.21, 95% CI=2.30–22.58, p=0.001; 12-month odds ratio=12.56, 95% CI=3.26–48.44, p<0.001). Similarly, psychotic experiences reported at baseline predicted bullying at 3 months, even after adjusting for baseline reports of bullying (3-month odds ratio=5.32, 95% CI=1.16–24.40, p=0.032). There was a nonsignificant trend for psychotic experiences reported at baseline to predict bullying at 12 months after adjusting for baseline reports of bullying (odds ratio=3.22, 95% CI=0.53–19.60, p=0.20).

A number of criteria have been put forward, based on the U.S. Surgeon General’s seminal report on smoking and health, to judge whether an epidemiological association is causal (25). A necessary, though insufficient, criterion to establish a causal relationship is temporality; that is, exposure to the supposed cause must precede the effect. Other criteria that support a causal relationship include 1) strength of association—the stronger the association, the more likely that it is causal; 2) dose-response relationship—as the dose of exposure increases, so should the odds of the outcome increase; 3) cessation of exposure—if exposure ceases or decreases, then the odds of the outcome should cease or decrease; 4) consideration of alternative explanations; and 5) biological plausibility.

This study demonstrated a clear temporal relationship between exposure to childhood trauma and the onset of psychotic experiences, looking only at the effect of trauma exposure on individuals who were free of psychotic symptoms at baseline. The strength of this relationship, in terms of odds ratios, was large. We demonstrated a dose-response relationship between childhood trauma and psychotic experiences, with the odds of psychotic experiences increasing in line with increasing levels of bullying (see Table 3). Beyond this, we demonstrated that cessation of childhood trauma was associated with cessation of psychotic experiences: in individuals who had been exposed to childhood trauma, cessation of traumatic experiences predicted a significantly reduced incidence of psychotic experiences compared with individuals for whom the traumatic experiences continued. We also assessed the important alternative explanation that psychotic experiences may lead to exposure to childhood trauma rather than vice versa. There was evidence that this was the case and that there is in fact a bidirectional relationship between childhood trauma and psychotic experiences. There are a number of possible explanations for this. One is that psychotic experiences may lead to behavior that attracts hostile or bullying responses. Another is that children with psychotic experiences may live in social circumstances where traumatic experiences are more likely to happen, in which case psychotic experiences may predict traumatic experiences but not necessarily cause them. A third is that children with psychotic experiences may interpret negative interactions with others in a more paranoid way and may be more likely than children without psychotic experiences to label such experiences as bullying. There is less room for misinterpretation of intention, however, when it comes to physical assault. In any case, by removing all individuals with baseline psychotic experiences from our analysis, we removed the possibility that psychotic experiences were responsible for subsequent childhood trauma. Even after these strict adjustments, we found that traumatic experiences predicted new incidences of psychotic experiences.

In relation to biological plausibility, a growing body of research has demonstrated important biological sequelae of childhood trauma. In a recent genome-wide methylation study of victims of childhood trauma, for example, Labonté et al. (30) showed a host of differentially methylated promoter regions within the genome relative to comparison subjects. Genes involved in cellular/neuronal plasticity were most significantly affected, in line with findings of increased risk for psychiatric illness. Childhood trauma also appears to have negative effects on catecholamine regulation and hypothalamic-pituitary-adrenal axis function. Sensitization of the pituitary-adrenal and autonomic stress response has been demonstrated both in mouse models of childhood trauma (31) and in human victims of abuse (32). Catecholamine deregulation resulting from this may lead to an increased propensity for psychotic reactions to stressful events. Complementary psychological theories have also presented hypotheses on how psychotic experiences may result directly from repeated exposure to childhood trauma (15, 33, 34). Research suggests, for example, that exposure to childhood trauma can result in the development of negative schematic beliefs about the self and others and that these negative beliefs may result in a sense of powerlessness, a lack of agency, a view of the self as vulnerable, and appraisals of normal events as threatening, ultimately manifesting in paranoia and misinterpretation of normal stimuli (15, 33–38). This work has been supported empirically by recent research suggesting that childhood trauma may have a direct impact on self-esteem, locus of control, and symptoms of depression and anxiety and that this may in turn lead to the onset of psychotic experiences (22).

An encouraging finding of the present study is that cessation of physical abuse and bullying was predictive of cessation of psychotic experiences. This suggests that intervention may lead to reduced psychotic experiences in the population. Since most bullying occurs in the school (39), one approach that we would advocate is an increased emphasis in teacher training on the role of the teacher in bullying prevention and intervention. Bullying is more severe in schools where teachers are lax about bullying intervention (40), and the degree of commitment of the teaching staff to bullying intervention is important to the success of such interventions (39). While the emphasis in teacher training is typically on knowledge and understanding of the curriculum, we would advocate a shift in emphasis so that the focus is on overall healthy child development from a much broader perspective than the acquisition of a certain set of educational skills. We would argue that training on the provision of a safe and positive environment that promotes optimal overall child development should form the core of teacher training programs. Formal training on evidence-based interventions to prevent and stop bullying (39) should form the backbone of such a program. This approach would also be beneficial in addressing physical assaults, since the single biggest group responsible for perpetrating physical assaults in the present study was schoolmates.

A notable strength of this study is its longitudinal nature, which allowed us to assess whether childhood trauma predicted psychotic experiences over time and vice versa. We used prospective measures of trauma collected repeatedly over 12 months, rather than retrospective assessments of trauma that occurred over the entire lifetime. Furthermore, our sample was population based and nationally representative, allowing us to generalize our findings to the community. A limitation is that it is not possible to know the degree to which the objectively adverse events (physical assault and bullying) were subjectively traumatic to the individuals: for some, a physical assault may have been extremely traumatic, while for others the event may not have had a severe subjective impact. Future research should attempt to assess the degree to which the objective event was subjectively traumatic, as this may have an impact on risk for psychotic experiences. Physical assault and bullying were self-reported in the study, without independent confirmation. However, research has shown that even individuals with severe mental illness, including psychotic disorders, tend to be as accurate in recalling abusive experiences as other individuals in the general population (41, 42). The types of traumatic experiences investigated in this study were limited to physical assault and bullying. A number of studies have reported an association between a wider range of traumatic experiences and psychosis, most notably sexual abuse (2, 42, 43). It will be beneficial to repeat our findings with expanded measures of trauma. Research incorporating data on potential mediating factors in the relationship between trauma and psychotic experiences will also be beneficial. Alemany et al. (44), for example, found that psychotic experiences were associated with an interaction between trauma and the brain-derived neurotrophic factor Val66Met polymorphism. Fisher et al. (22), meanwhile, found that the relationship between childhood trauma and psychotic experiences may be partially mediated by effects of trauma on self-esteem, locus of control, and symptoms of depression and anxiety. Further research incorporating data on potential biological and psychological mediators will be valuable. Our assessment of psychotic experiences was based on a validated item with established high positive and negative predictive value for psychotic symptoms in the general adolescent population (29). However, the face validity for this item is for hallucinations, and its high positive and negative predictive value for psychotic symptoms in adolescence may be related to the fact that hallucinations are more common than delusions in this age group (29). Further research looking specifically at older populations, in which delusional beliefs are more common, will be beneficial for determining the causal relationship between trauma and delusions specifically.