Despite age at onset (AAO) of eating disorders (EDs) has classically been described in adolescence; to date there is not an univocal definition. While initial studies described a bimodal distribution of AAO for ED, recently several studies didn’t confirm these findings.

AAO thresholds definition for anorexia nervosa (AN) and bulimia nervosa (BN) with statistical validation of proposed cut-offs is highly needed, since AAO represents a crucial clinical feature.

We obtained data from subjects with AN and BN to perform a normal distribution admixture analysis to determine their AAO.

A total of 806 ED patients (792 females; 379 AN and 427 BN) were recruited. Diagnosis of AN and BN were ascertained according to the DSM-IV-TR criteria by means of the SCID – Patient Edition. AAO was assessed by a clinical interview performed by a psychiatrist matched with a systematic review of medical records. To test AAO subgroups, we used a normal distribution admixture analysis.

A bimodal normal distribution of AAO with an early onset and late onset component was found for both AN and BN. Most of the subjects with AN (75.3%) and BN (83.3%) belonged to the early onset group. Both groups had a mean AAO of about 18 years. No significant differences were found concerning the AAO between groups.

Consider clinical history and course of AAO for EDs may be crucial for planning treatment. To our knowledge, this is the first study that applied a validated statistical procedure to identify AAO cut-off points for AN and BN.

The authors have not supplied their declaration of competing interest.