Shared and unique risk factors between lifetime purging and objective binge eating: a twin study.

BACKGROUND Objective binge eating (OBE) and self-induced vomiting (SIV) occur and co-occur across a range of eating disorders but the extent to which the risk factors for these two behaviours overlap is unclear. Examination of this overlap was the focus of the current report. METHOD A population of female Australian twins (n=1002), mean age 35 years (s.d.=2.11, range 28-40), participated in three waves of data collection and were assessed for lifetime disordered eating with a semi-structured interview at wave 3 and a self-report questionnaire at wave 1; risk factors were assessed via a self-report at waves 1 and 3. RESULTS Non-shared environmental influences were the largest contributor to the variance of both OBE and SIV, with a more modest contribution of genetic influences. Between 5% and 14% of the environmental risk factors for OBE and SIV were shared and 27-100% of genetic risk factors were shared. SIV initiation was predicted by higher neuroticism and novelty seeking and lower maternal and paternal care, whilst lower levels of perceived paternal care, higher lifetime BMI, and a wider BMI range predicted OBE initiation. Retrospective correlates associated with both SIV and OBE onset were parental comments about weight, whilst higher levels of parental conflict, expectations and criticism was associated with OBE onset only. CONCLUSIONS The substantial extent of non-overlap between risk factors for SIV and OBE suggests that each of these behavioural disturbances warrants future investigation in its own right, not only when they occur in conjunction with each other.