Leisure, Commuting Sitting Time Associated With Lower BMD After Adjustment for Physical Activity

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Sitting time was associated with bone mineral density after adjustment for physical activity.
Sitting time was associated with bone mineral density after adjustment for physical activity.

New findings from a population-based cohort study suggest that there are small but significant deficits in hip bone mineral density (BMD) cross-sectionally associated with sitting time adjusted for physical activity.

The results were presented at the American Society for Bone and Mineral Research (ASBMR) 2016 Annual Meeting.

In the study, Jerilynn C. Prior, BA, MD, of the University of British Columbia in Vancouver, and colleagues assessed data from the Canadian Multicentre Osteoporosis Study (CaMos) to determine whether sedentary behavior (sitting time in commuting and television watching) was linked with BMD in population studies, since that could have implications for falls and fracture prevention.

The analysis included baseline relationships of 8330 adult Canadians (68.9% women) evaluated during 1995 to 1997 who had available BMD at the spine, femoral neck, or total hip.

Researchers determined sitting time in 2 ways: totaling reported time spent sitting watching television and traveling and by reported time spent sitting at work.

Data indicated the following mean BMD values:

  • Lumbar spine (L1-L4): women, 0.937 g/cm2; men, 1.047 g/cm2
  • Femoral neck: women, 0.707 g/cm2; men, 0.810 g/cm2
  • Total hip: women, 0.854 g/cm2; men, 1.010 g/cm2 

Weekly median times for total physical activity were 1.8 hours in women vs 7.3 hours in men, while both genders spent 21 hours per week sitting watching television or in travel.

In addition, data revealed that among women, mean BMDs in third and fourth quartiles of the lumbar spine, femoral neck, and total hip were reduced compared with the mean BMDs in the first quartile. In men, however, no differences in the quartiles were observed in the spine, but the mean femoral neck and total hip BMDs were lower in the third quartile compared with the first quartile.

Researchers also reported that nonsignificant results existed for total hip BMD and that for the sitting at work variable, no significant relationships were observed for spinal, femoral neck, or total hip BMD.

“Overall in these data, the relationship between sitting time and BMD was usually nonsignificant, and was nowhere near as consistently strong as the relationship between physical activity and BMD,” Dr Prior and fellow researchers wrote in the abstract. However there is an important trend to lower hip site BMD values in women and men with longer vs shorter durations of leisure/commuting sitting despite adjustment for moderate-strenuous physical activity, they noted.

Disclosure: Dr Prior reports no relevant financial disclosures.

For more coverage of ASBMR 2016, click here.

Reference

  1. Prior JC, Drayton B, Pedisic Z, Berger C, Goltzman D, Bauman A. Abstract LB-SA0374. Is sitting time (sedentary behaviour) associated with bone mineral density?  Results from the CaMos population-based cohort. Presented at: ASBMR 2016 Annual Meeting; September 16-19, 2016; Atlanta, Georgia. 
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