Sedentary behaviour and bone health in children, adolescents and young adults: a systematic review-supplementary presentation.

BACKGROUND: Sedentary behaviour (SB) is a potential risk factor for suboptimal bone deposition in youth.
RESULTS: Total SB was negatively associated with lower extremity bone outcomes, while no association was observed with total body bone outcomes. Insufficient evidence was found for an association between total SB and lumbar spine bone outcomes.
CONCLUSION: This review highlights the heterogeneity of the available evidence and emphasizes the need for well-designed studies.

Aim

The aim of this systematic review was to examine the association between SB and bone health in children, adolescents and young adults [1].

Key findings

Based on studies that used DXA and quantitative ultrasound, we found moderate evidence for a negative association between objectively measured SB and lower extremity bone outcomes in schoolchildren that was independent of moderate-to-vigorous physical activity (MVPA). We calculated that 1 h less sedentary time per day is associated with the same effect on femoral neck bone mineral density (BMD) as 18 min of MVPA (based on one high-quality study). Based on high-quality studies that used DXA, there was strong evidence to suggest no association between objectively measured SB and total body bone outcomes in schoolchildren, and insufficient evidence for an association with lumbar spine bone outcomes. For questionnaires, none of these relationships were observed.

Importance, timeliness and interest

This systematic review suggests that objectively measured total sedentary time is negatively associated with bone outcomes of the lower extremities in schoolchildren.

Although the magnitude of the effect size seems small, it may theoretically be relevant for bone accrual in the young, in particular when the SB is maintained over several years. Furthermore, this review highlights the heterogeneity of the available evidence (different bone-imaging tools, measurement of SB, anatomical sites assessed, outcome parameters, adjustment of results) and emphasizes the need for well-designed studies.

Significance of findings

Optimizing bone accrual in the young is important to minimalize the risk of osteoporosis in later life. If the effect of SB on lower extremity bone outcomes is confirmed in other studies, reducing sedentary time could be helpful to optimize bone accrual in children who are unable or less interested in PA.

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