Bone Abstracts

Introduction: Whilst it is well-established that sedentary behaviour may increase the risk of paediatric obesity, and potentially result in early onset cardio-metabolic diseases such as type 2 diabetes and cardiovascular disease, there is less consensus about the potential detrimental effects that long-term sedentary behaviour may have on bone health during childhood.

Purpose: To determine if long-term sedentary behaviour affects accrual of bone mass, structure and strength during childhood.

Methods: A total of 99 (girls=45) children (mean age 12.2+0.8 years) were categorized into sustained high (n=43) and low (n=56) levels of sedentary behaviour (≤100 counts/min) based on at least two objective (Actigraph accelerometer worn for >4 days) sedentary behaviour measurements assessed at three year intervals from pre-school age to thirteen years. Peripheral quantitative computed tomography (pQCT) was used to assess the total bone area (ToA), cortical density (CoD), cortical area (CoA), marrow density (MaD), polar strength strain index (SSIp) and total cortical and regional (endo-, mid- and peri-cortical) vBMD at the mid (66%) tibia and radius. Bone outcomes were compared across groups adjusting for maturity offset and gender using analysis of covariance followed by post hoc pairwise comparisons with Bonferroni adjustments.

Results: There were no significant differences in height, weight or BMI z-scores between groups. At the tibia, when adjusting for maturity offset and gender, children with more sedentary time across childhood had 7.4% lower ToA, 8.0% lower CoA and 9.0% lower SSIp, and 2.0% greater CoD (P<0.05) compared to the active group. Sex-specific analyses showed that these significant differences persisted in boys, but not in girls, with those spending more time in sedentary behaviour having 11.1–14.9% lower CoA and SSIp (P<0.05) compared to their active peers. At the Radius there were no significant differences between groups.

Conclusion: Long-term sedentary behaviour during childhood is associated with decreased total and cortical bone size and strength, which may increase fracture risk at the mid-tibial shaft. Although cortical density at the weight-bearing tibia appears to be greater following long-term sedentary behaviour, this may be due to increased activity resulting in greater bone turnover among the more active children.

Disclosure: The authors declared no competing interests.