Physical activity and bone health in schoolchildren: the mediating role of fitness and body fat.
BACKGROUND
The relationship between physical activity (PA) and bone health is well known, although the role of percent body fat (%BF) and fitness as confounders or mediators in this relationship remains uncertain.


OBJECTIVE
To examine whether the association between PA and bone mineral content (BMC) is mediated by %BF and cardiorespiratory fitness (CRF).


METHODS
In this cross sectional study, BMC, total %BF (by DXA), vigorous PA (VPA), CRF, age and height were measured in 132 schoolchildren (62 boys, aged 8-11 years). ANCOVA was used to test differences in BMC by %BF, CRF and VPA, controlling for different sets of confounders. Simple mediation analyses and serial multiple mediation analyses were fitted to examine whether the relationship between PA and BMC is mediated by %BF and fitness.


RESULTS
Children with high %BF had higher total body BMC than their peers after controlling for all sets of confounders. Children with good CRF or VPA had significantly less total body BMC after controlling for age and sex but in children with good CRF this inverse relation disappeared after adjusting by %BF. %BF and CRF both act as a full mediator in the association between VPA and BMC, after inclusion of the potential confounders in the models.


CONCLUSIONS
Fitness and %BF seem to have a mediator role on the relationship between physical activity and bone mass.
School of Nursing and Physiotherapy, University of Castilla La Mancha, Toledo, Spain.
Ana
A
Torres-Costoso
CHERC (Children's Health and Exercise Research Centre) Sport and Health Sciences, University of Exeter, Exeter, United Kingdom; GENUD "Growth, Exercise, Nutrition and Development" Research Group, University of Zaragoza, Zaragoza, Spain.
Luis
L
Gracia-Marco
Social and Health Care Research Center, University of Castilla La-Mancha, Cuenca, Spain; Faculty of Education, University of Castilla La Mancha, Ciudad Real, Spain.
Mairena
M
Sánchez-López
Social and Health Care Research Center, University of Castilla La-Mancha, Cuenca, Spain.
Blanca
B
Notario-Pacheco
Social and Health Care Research Center, University of Castilla La-Mancha, Cuenca, Spain.
Natalia
N
Arias-Palencia
Social and Health Care Research Center, University of Castilla La-Mancha, Cuenca, Spain; Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Talca, Chile.
Vicente
V
Martínez-Vizcaíno
D000273:Adipose Tissue / Q000033:anatomy & histology / Q000502:physiology*; D015519:Bone Density; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D010809:Physical Fitness