Age of onset has limited association with body mass index at time of presentation for anorexia nervosa: comparison of peak-onset and late-onset anorexia nervosa groups.

The clinical characteristics differentiating late-onset anorexia nervosa (AN) from typical pubertal onset AN remain unclear. The purpose of the present study was to examine these differences in a retrospective analysis. A total of 149 female AN patients was divided into two groups: a peak-onset AN group (n = 125) in which onset occurred between the ages of 15 and 24 years, and a late-onset AN group (n = 24) in which onset occurred at the age of > or =25 years. A logistic regression analysis was conducted with this classification as the target variable and five clinical factors as explanatory variables for the clinical characteristics at the time of initial examination. Body mass index (BMI) at the time of presentation was identified as a possible factor affecting classification as peak-onset or late-onset AN. In addition, a negative linear correlation was detected between age of onset and BMI at the time of initial examination. The results suggest that BMI at the time of the initial examination is an important clinical characteristic to differentiate peak-onset AN and late-onset AN.