Adiposity and TV Viewing Are Related to Less Bone Accrual in Young Children

Abstract

Objective-To examine the relation between baseline fat mass and gain in bone area and bone mass in preschoolers studied prospectively for 4 y, with a focus on the role of physical activity and TV viewing.Study design-Children were part of a longitudinal study in which measures of fat, lean and bone mass, height, weight, activity, and diet were taken every 4 months from ages 3 to 7 y. Activity was measured by accelerometer, and TV viewing by parent checklist. We included 214 children with total body dual energy x-ray absorptiometry (Hologic 4500A) scans at ages 3.5 and 7 y.Results-Higher baseline fat mass was associated with smaller increases in bone area and bone mass over the next 3.5 y (p<0.001). More TV viewing was related to smaller gains in bone area and bone mass accounting for race, sex, and height. Activity by accelerometer was not associated with bone gains. Conclusions-Adiposity and TV viewing are related to less bone accrual in preschoolers.Keywords bone mineral; preschool; fat mass; sedentary; obesity; outdoor play While it is known that the strength of bone is its resistance to fracture and largely reflects skeletal adaptation to muscle forces, the impact of obesity on bone strength in children is unclear 1, 2 . Obesity might promote increases in bone strength to support the locomotion of a heavy body mass; higher adiposity in children is related to greater bone area and BMC. 3-5 If overweight children have a bone strength advantage, it might be due to the greater muscle force needed to move a larger body mass. On the other hand, in adults of similar weight, those with more fat mass have lower bone mass 6 and higher fracture risk 7 . In studies of children, some Corresponding author: Karen S. Wosje, PhD Cincinnati Children's Hospital Medical Center Division of General and Community Pediatrics ML 7035, 3333 Burnet Ave, Cincinnati, OH 45229-3039 513-636-2412 voice; 513-636-4402 fax; karen.wosje@cchmc.org. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.No reprints requested.The authors declare no conflicts of interest. have reported that forearm fracture risk is greater in children with more fat mass, 8, 9 whereas others have not. 10 Part of the increased fracture risk with greater fat mass may be due to poorer balance 11 and higher impact force with falling in heavier children. 12 Children with greater relative fat mass may be more prone to fracture because they have lower bone mineral content (BMC). 13, 14 . Muscle mass is more strongly correlated with BMC than is fat mass in children, 15 so overweight children with low muscle mass may still have low ...

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