| dc.description.abstract | Childhood and adolescence are a crucial period for determining peak bone mass, which is a risk factor for the lifetime risk of osteoporosis. However, there is a lack of evidence regarding the associations between lifestyle factors, endocrine factors, and body composition with bone in this demographic. This thesis used data from the Physical Activity and Nutrition in Children (PANIC) Study, a longitudinal study in a population sample of Finnish children, to investigate the cross-sectional and longitudinal associations of physical activity (PA) and other movement behaviours, vitamin D status, lean mass, and fat mass and associated endocrine factors, with bone mass. Chapter 4 showed that moderate PA, moderate-to-vigorous PA (MVPA), and vitamin D status were independently positively associated with bone mass in children aged 6 to 8 years. Chapter 5 applied novel mediation analysis methods and revealed a positive association between fat mass and bone mass in children aged 9 to 11 years, which was suppressed by mediation through free leptin index in both sexes, and moderated by adiponectin and free leptin index in females and males respectively. Chapter 6 used novel methods of summarising PA data in 9 to 11 year olds. PA volume was positively associated with bone mass in females and males, and PA intensity distribution was negatively associated with bone mass in males. Chapter 7 found that MVPA was positively associated with bone mass longitudinally in females, and that time spent in sport and exercise participation was positively associated with bone mass longitudinally in females and males. Sedentary time, screen time and sleep were not associated with bone mass longitudinally. These findings contribute to the literature by providing novel insights into the relationships between PA, summarised with different
assessment methods and metrics, body composition, and associated endocrine factors, and vitamin D status, with bone mass in children and adolescents. This thesis emphasises the importance of utilising different methods for assessing and summarising PA, and supports the consideration of fat and lean mass when looking at relationships between PA and bone mass. Further, the importance of PA promotion and behaviours to encourage improved vitamin D status to improve children’s bone health during growth are highlighted. | en_GB |
