Association between sedentary behavior and bone mass, microstructure and strength in children, adolescents and young adults: a systematic review.

Sedentary behavior (SED) research is currently receiving increasing attention in the field of public health. While it has been shown to have negative effects on cardiovascular or metabolic health, there is limited knowledge regarding the relationship between SED and bone health in children, adolescents, and young adults. Thus, the purpose of this review is to investigate the associations between SED and bone health status, specifically bone mass, microstructure, and strength. A comprehensive literature search was conducted across five electronic databases, including EMBASE, PubMed, Medline, Cochrane, Web of Science and CNKI. The inclusion criteria were as follows: healthy participants aged 24 years or younger, with measured SED and measured bone outcomes. The quality of the included articles was assessed using the National Institute of Health Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. After excluding, the final sample included 25 cross-sectional, 9 observational and 2 both cross-sectional and longitudinal studies. Among these, seven were rated as 'high quality', twenty-three were rated as 'moderated quality', and six were rated as 'low quality' according to the quality assessment criteria. After summarizing the evidence, we found no strong evidence to support an association between BMC or BMD and SED, even when considering gender or adjusting for moderate-to-vigorous physical activity (MVPA). However, a strong level of evidence was found indicating a negative relationship between objectively measured SED and cortical bone mineral density (Ct.BMD) in the tibia or stiffness index (SI) in the Calcaneus across all age groups. While the association between adverse bone health outcomes and SED still cannot be confirmed due to insufficient evidence, these findings suggest that bone microstructure and strength may be more sensitive to SED than bone mass. Thus, further evidence is needed to fully understand the connection between sedentary behavior and bone health, particularly regarding the relationship between SED and bone strength.