Bipolar disorder is a mental illness characterised by swings from extremely high to extremely low moods. Experiencing these mood swings can be very debilitating, and many people with bipolar disorder are impaired in their day-to-day lives.

In the search for possible causes, researchers have examined the childhood experiences of people with bipolar disorder. There is evidence suggesting that people with bipolar disorder are more likely to have experienced adversity when they were young, such as abuse and neglect, compared to healthy adults. However, most of the studies are conducted in relatively small samples and the findings are not always consistent.

The aim of a recent study by Palmier-Claus and colleagues was to meta-analyse results from all studies examining rates of childhood adversity in bipolar disorder, to test whether there was an overall association between the two.

Methods

The authors conducted a systematic review and meta-analysis. They began by searching the psychology and psychiatry literature for studies published between 1980 and 2014 that had bipolar disorder and childhood adversity as their topic. Studies had to be published in peer-reviewed, English-speaking journals.

This initial search yielded 5,395 studies. However, the number decreased as the authors applied stricter criteria. Studies had to be epidemiological or clinical case-control studies that compared rates of childhood adversity between two groups of individuals: those with a diagnosis of bipolar disorder and those without a diagnosis of bipolar disorder or related psychiatric problems, such as depression and schizophrenia.

Childhood adversity was defined as having experienced neglect, abuse, bullying or the death of a parent before age 19. The authors did not include spanking or shouting by caregivers as child adversity, because they assumed these practices to be subject to cultural variability. Childhood adversity did not include divorce, or growing up in difficult circumstances, such as in poverty.

Applying these inclusion criteria narrowed the number of studies down to 19 that were deemed eligible for analysis. The majority were clinical case-control studies, altogether comprising over a thousand individuals with a diagnosis of bipolar disorder, and a similar number of controls. Six studies were epidemiological studies, with altogether over 2 million participants. From these studies, the authors extracted the statistics needed to conduct a meta-analysis.

Results

There were four main results:

1. Childhood adversity was overall more common in adults with a diagnosis of bipolar disorder, compared to those without
   • Of the 19 studies, 15 found such a difference
   • However, the size of the effect varied across studies, with some reporting larger differences than others
   • The authors did not find evidence for publication bias, suggesting little selective publishing of studies.
2. Adults with bipolar disorder had experienced higher rates of childhood adversity across all its forms, including physical and sexual abuse as well as physical and emotional neglect
   • Associations were particularly high for emotional abuse
   • The only non-significant difference between cases and controls was for parental loss.
3. Rates of adversity did not differ among individuals with different types of bipolar disorder
   • Bipolar disorder type I and type II are distinguished based on their symptoms: type I is characterised by periods of mania and type II by attenuated mania
   • However, as the results show, even though individuals with different types have different symptoms, they are both at equally high risk of having experienced childhood adversity.
4. People with bipolar disorder experienced similar rates of adversity as people with schizophrenia and depression, although the results of comparisons for the latter were more ambiguous
   • This result suggests that rates of childhood adversity are elevated in several psychiatric problems; not just bipolar disorder.

Strengths and limitations

This is a comprehensive study that did not only compare childhood adversity across people with bipolar disorder and controls, but also examined different types of childhood adversity and psychiatric problems. However, there are some limitations:

• A relatively large number of studies was excluded because of what the authors describe as “no valid assessment of bipolar disorder” or “no valid trauma assessment”. It would have been useful to have the characteristics of these excluded studies discussed in more detail, so that future meta-analyses are able to consider whether to broaden their exclusion criteria to include some of them
• Only studies with formal diagnoses of bipolar disorder were included, rather than symptoms or subthreshold disorder, which might have extended the evidence base
• No information was provided on the average age of individuals diagnosed with bipolar disorder. This would have been interesting, to evaluate how likely it may be that bipolar disorder predicted exposure to adversity rather than vice versa
• It was not possible to examine possible explanations for the sizeable variation of effect sizes across the studies.

Implications

This study contributes to a large body of evidence showing higher rates of childhood adversity in people with psychiatric problems. There are several interesting future questions that the findings of the study raise:

• Virtually all of the studies in the meta-analysis assessed childhood adversity retrospectively, i.e. by asking adults to recall their experiences during childhood. Such studies are prone to biases, for example if adults with bipolar disorder are better at remembering adversity. To test whether this affects the findings, more longitudinal studies are needed that assess adversity in children and then follow them up into adulthood, to examine whether they are more likely to develop bipolar disorder.
• Longitudinal study designs would also be helpful in establishing whether adversity is a risk factor for bipolar disorder. The findings of the meta-analysis show that there is a link between adversity and bipolar disorder, but not whether adversity causes disorder. It is possible that there are factors that make individuals more likely to experience adversity and to develop bipolar disorder, for example growing up in deprivation or having violent parents. More studies are needed to examine this possibility.
• Finally, it would be interesting to examine which specific symptoms adversity affects. For example, the meta-analysis showed that adversity was associated not only with bipolar disorder but also with schizophrenia and, to a lesser extent, depression. Thus, it is possible that adversity is linked with an individual’s general risk for psychopathology, rather than one specific problem per se. It is also possible that it is associated with psychotic symptoms more specifically, which occur in some individuals with severe bipolar disorder and depression, as well as in schizophrenia. Future studies will help answer these questions.

Links

Primary paper

Palmier-Claus JE. et al (2016) Relationship between childhood adversity and bipolar affective disorder: systematic review and meta-analysis. The British Journal of Psychiatry 1–6. doi: 10.1192/bjp.bp.115.179655 [BJPsych abstract]

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