Bone mineral density in Anorexia Nervosa versus Avoidant Restrictive Food Intake Disorder

Avoidant Restrictive Food Intake Disorder (ARFID) and Anorexia Nervosa (AN) cause significant underweight in children and young people (CYP). The association of low bone mineral density (BMD) and underweight CYP in AN is well established, but less is known about BMD in ARFID.

Retrospective case-note review and analysis of BMD measures by DXA on underweight patients referred to a paediatric clinic for eating disorders between 2014 and 2019. Indications for BMD measurement were age > 5 years and underweight for at least 6 months.

Of 134 cases where BMD was measured, 118 (88%) had AN and 16 (12%) ARFID. Age range was 6-19 years. 19% were males. ARFID cases were more likely to be male, have lower Body Mass Index (BMI), BMI z-score (BMIz), and longer underweight duration. For all cases, BMI and BMIz were positively associated with BMD z-score (BMI: coefficient 0.13,95%CI 0.04 to 0.22, p = 0.01; BMIz: coefficient 0.34, 95%CI 0.17 to 0.51, p < 0.001) and bone mineral areal density z-score (BMI: coefficient 0.12, 95% CI 0.01 to 0.23, p = 0.04 and BMIz: coefficient 0.27, 95% CI 0.05 to 0.49, p = 0.02). However, there were no associations of BMD with diagnosis (ARFID vs AN). Paired t-testing of 13 age, sex and pubertally matched pairs from AN and ARFID cases also showed no difference in standardized BMD scores.

Low BMD in our sample of underweight AN and ARFID cases was associated with BMI but not diagnosis. BMD may be as important in ARFID as AN. Further research should examine mechanisms and potential interventions.