In Reply We thank Poulton and Lee for their suggestion to repeat our analysis using “actual weights instead of age and z scores.” While we are in agreement regarding an effect of weight on bone mass, we strongly feel that we used the most appropriate statistical model to analyze the cross-sectional population data presented in our study, as discussed here.
Age, sex, and height z score are critically important in the interpretation of pediatric dual-energy x-ray absorptiometry data because they account for the dynamic nature of bone accrual. Weight certainly has an effect on bone mass owing to the load-bearing role of the skeleton; however, when analyzing population data it is most appropriate to use z scores. Per the World Health Organization, “for population-based assessments, including surveys, the Z-score is widely recognized as the best system for analysis and presentation of anthropometric data.”1 Furthermore, it is muscle, or lean mass, that is responsible for the strength of children’s load-bearing bones, and it is incorrect to assume that higher weight equates to greater muscle mass.2,3 In Poulton et al’s study assessing stimulant effects on bone and body composition, initial weight loss was associated with a reduction in fat mass concomitant with a “significant rise in lean tissue.”4 Even in the context of lower weight, patients had greater lean mass that should support bone accrual, not hinder it. Because the National Health and Nutrition Examination Survey does not include body composition data, we adjusted for weight using z scores per World Health Organization recommendations.1
Feuer AJ, Thai A. Stimulant Use and Bone Mineral Density—Reply. JAMA Pediatr. 2017;171(5):495. doi:10.1001/jamapediatrics.2017.0183
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