The findings reported by Ciro Marangoni and colleagues  made for some interesting reading recently and their systematic review of longitudinal studies looking at the various environmental exposures put forward as possible risk factors pertinent to the development of bipolar disorder (BD).
Trawling through the peer-reviewed material on this topic, the authors were able to 'clump' the various proposed risk factors into one of three categories: "neurodevelopment (maternal influenza during pregnancy; indicators of fetal development), substances (cannabis, cocaine, other drugs - opioids, tranquilizers, stimulants, sedatives), physical/psychological stress (parental loss, adversities, abuses, brain injury)."
They did not however, report the presence of any specific 'smoking gun' on the basis of their investigations, concluding that: "Only preliminary evidence exists that exposure to viral infection, substances or trauma increase the likelihood of BD." That also the various risk categories seemed to be 'correlated' with various other psychiatric and/or behavioural labels is also an important point to make in these days of overlap and RDoC.
I personally am not surprised by these results. Appreciating that diagnostic labels do not equal homogeneous groups, and that just as when defining the genetics of something like BD, so defining the non-genetic correlates is an equally difficult task, studies of this type remind us just how complicated and individual the paths are bringing someone to such a clinically-relevant label. I say this with the understanding that just because an specific environmental (or non-environmental) risk factor might not be generalisable to all BD does not mean it can't exert a more pronounced effect in smaller groups or individuals. Lessons from other labels teach us this (see here).
Whilst important to understand whether there may be specific environmental exposures that might be more generally linked to an enhanced risk of developing BD, I do believe that the [research] future lies in a couple of other areas looking at: (a) how many different types of BD are there and what are the 'other' conditions/labels potentially related? (b) what does the biology of BD look like and does it include some common targets with other labels? and (c) outside of the array of interventions put forward for managing symptoms (see here), are there other intervention strategies that might fit with the findings of (a) and (b)?
To close, LEGO do it best...
 Marangoni C. et al. The role of environmental exposures as risk factors for bipolar disorder: A systematic review of longitudinal studies. J Affect Disord. 2016 Jan 1;193:165-174.
Marangoni C, Hernandez M, & Faedda GL (2016). The role of environmental exposures as risk factors for bipolar disorder: A systematic review of longitudinal studies. Journal of affective disorders, 193, 165-174 PMID: 26773919
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