Associations between objectively-measured sedentary behaviour and physical activity with bone mineral density in adults and older adults, the NHANES study

These results provide the first evidence that repeated exposure to sitting (SB), measured objectively in daily life, is deleteriously associated with BMD of the total femur and of all hip sub-regions in women, independent of the amount of time women engage in moderate and vigorous activity. This suggests that SB might be a risk factor for bone health in women independent of whether they engage in physical activity. In addition, the duration of SB bouts, rather than their frequency, appears to be deleteriously associated with BMD of the total femur and of all hip sub-regions. Future research should investigate the effect on bone health of interventions which set out to reduce SB and the duration of SB bouts in comparison, and as adjunct, to the promotion of PA. For men, SB is not significantly associated with BMD of the femur or spine and the results appear to confirm that moderate and vigorous activity has a protective effect.