Risk factors in relation to an emergence of bipolar disorder: a systematic review.

OBJECTIVE There is a consensus that genetic factors are important in the causation of bipolar disorder (BPD); however, little is known about other risk factors in the aetiology of BPD. Our aim was to review the literature on such risk factors - risk factors other than family history of affective disorders - as predictors for the initial onset of BPD. METHODS We conducted a literature search using the MEDLINE, PsycINFO and EMBASE databases. We selected factors of interest including demographic factors, factors related to birth, personal, social and family backgrounds, and history of medical conditions. The relevant studies were extracted systematically according to a search protocol. RESULTS We identified approximately 100 studies that addressed the associations between antecedent environmental factors and a later risk for BPD. Suggestive findings have been provided regarding pregnancy and obstetric complications, winter-spring birth, stressful life events, traumatic brain injuries and multiple sclerosis. However, evidence is still inconclusive. Childbirth is likely to be a risk factor. The inconsistency across studies and methodological issues inherent in the study designs are also discussed. CONCLUSION Owing to a paucity of studies and methodological issues, risk factors of BPD other than family history of affective disorders have generally been neither confirmed nor excluded. We call for further research.