The sample is composed of 2200 AN subjects and 900 BN subjects without previous AN consecutively referred to our outpatient Unit in the period between 1985 and 2014. Time trends have been analysed according to the year of birth of subjects. All diagnoses were reviewed according to DSM-5 criteria.

Age of onset in AN showed a significant decrease according to year of birth. A regression model showed a significant independent effect of socio-economic status, age at menarche and number of siblings in predicting age of onset. A second analysis including a subsample representative of the general population confirmed the effect in AN. In BN, although the age of onset showed a decrease in new generations, the effect is not significant.

Age of onset of AN continues to decrease in younger generations. The implications of our findings in terms of long-term outcome remain to be understood. Biological and socio-cultural factors explaining this phenomenon need to be explored by future studies. It is important to acknowledge the clinical implications of this cohort effect.

The authors have not supplied their declaration of competing interest.