Sedentary behavior does not predict low BMD nor fracture - population-based Canadian Multicentre Osteoporosis Study (CaMos).

Sedentary behavior (SB) or sitting is associated with multiple unfavorable health outcomes. Bone tissue responds to imposed gravitational and muscular strain with there being some evidence suggesting a causal link between SB and poor bone health. However, there are no population-based data on the longitudinal relationship between SB, bone change and incidence of fragility fractures. This study aimed to examine the associations of sitting/sedentary behavior (defined as daily sitting time), areal bone mineral density (BMD by dual energy X-ray absorptiometry) and incident low trauma (fragility) osteoporotic fractures (excluding hands, feet, face and head). We measured baseline (1995-7) and 10-yr self-reported SB, femoral neck (FN), total hip (TH) and lumbar spine (L1-4) BMD in 5708 women and 2564 men aged 25-80+ years from the population-based, nation-wide, nine-center Canadian Multicentre Osteoporosis Study (CaMos). Incident 10-yr fragility fracture data were obtained from 4,624 participants; >80% of fractures were objectively confirmed by medical-records or radiology reports. Vertebral fractures were confirmed by qualitative morphological methods. All analyses were stratified by sex. Multivariable regression models assessed SB-BMD relationships; Cox proportional models were fit for fracture risk. Models were adjusted for age, height, BMI, physical activity and sex-specific covariates. Versus women with the least SB (1st quartile), women in 3rd/4th quartiles had lower adjusted FN BMD; women in the SB 3rd quartile had lower adjusted TH BMD. Men in the SB 3rd quartile had lower adjusted FN BMD than those in SB 1st quartile. Neither baseline nor stable 10-year SB were related to BMD change nor to incident fragility fractures. Increased sitting (SB) in this large, population-based cohort was associated with lower baseline FN BMD. Stable SB was not associated with 10-year BMD loss nor increased fragility fracture. In conclusion, habitual adult sedentary behavior was not associated with subsequent loss of BMD nor increased risk of fracture.