Body Mass Index (BMI) and Related Factors in a Large-Scale Study of Children with ASD and their Unaffected Siblings

Background: Only a few studies have explored height, weight, and BMI in autism spectrum disorder (ASD), with contradictory findings. Since it has been suggested that anthropomorphic differences may provide clues to the underlying biology of ASD, it is important to identify differences in BMI between affected and unaffected individuals.

Objectives: To analyze cross-sectional data on BMI, energy/activity level, and food intake for children with ASD, and their unaffected siblings, ages 3 to 17.

Methods: Parents provided data on height, weight, and related factors for 1,435 children with an ASD (85% male) and 1,011 of their unaffected siblings (47% male) using a web-based interface. Approximately half the measurements were obtained at a health provider’s office. Key variables were compared by ASD status, age group, and gender. A five point Likert scale was used to measure energy/activity level and food intake.

Results: Affected children ages 6-11 and 12-17, both girls and boys, had a significantly higher BMI compared with unaffected siblings (p<0.05). However, this was not the case for those ages 3-5. As expected, more girls and boys who were overweight had medical problems or were taking medications that are known to affect weight and/or height (p<0.05). Younger children with ASD had higher levels of hyperactivity, as compared to teenage children with ASD, who had low levels of energy/activity (p<0.001). Similarly, younger children with ASD were reported to eat a less-than-normal amount of food, while their teenage counterparts were reported to eat a more-than-normal amount of food (p<0.01). In contrast, a stable, more normal energy/activity level and amount of food consumed were reported for unaffected siblings.

Conclusions: There is a need to further explore the causes of elevated BMI in autism spectrum disorders, as well as to address the health risk this may pose.