315 South Bellefield Avenue, Pittsburgh, PA, 15260

A dissertation defense by Lauren S. Roe, Department of Epidemiology.

Committee:
Jane A. Cauley (advisor), Epidemiology
Elsa S. Strotmeyer, Epidemiology
Nancy W. Glynn, Epidemiology
Yan Ma, Biostatistics
Kellee Pettee Gabriel, University of Alabama at Birmingham, Department of Epidemiology
Peggy M. Cawthon, California Pacific Medical Center, Research Institute and University of California, San Francisco, Department of Epidemiology and Biostatistics

Abstract:

BACKGROUND: About 30% of older adults fall, and fractures are common consequences of falls that can lead to disability or death. Exercise/physical activity (PA) is the only non-pharmacologic prevention strategy that lowers fall and fracture risk. Inadequate sleep duration is an emerging risk factor for falls and is critical to bone metabolism for fracture prevention. PA, sedentary behaviors (SB), and sleep are often studied in isolation. Changes to time spent in one behavior necessitates changes to time spent in another behavior comprising a 24-hour day.

OBJECTIVES: To use compositional data analysis to evaluate associations between the combined role of PA, SB, and sleep with 1) incident fall and fracture risk, and their risk factors of 2) bone structure and microarchitecture using high-resolution peripheral quantitative computed tomography, and 3) muscle strength and power.

METHODS: Participants included community-dwelling older adults in the 1) Osteoporotic Fractures in Men (MrOS) study (n=2,918, age=78.9±5.1 years) and the 3) Study of Muscle, Mobility and Aging (SOMMA; n=714, age=76±5 years) and 2) Bone Ancillary (n=278) with 24-hour PA. Generalized estimating equations and cox proportional hazard regression estimated fall and fracture risk (paper 1). Multiple linear regression was applied by sex to cross-sectional analyses in papers 2 and 3. Compositional isotemporal substitution quantified changes to each outcome if time were theoretically substituted from one behavior to another.

RESULTS: Higher proportions of PA vs. remaining behaviors were associated with lower fall and fracture risk. Substituting 30 minutes SB for 30 minutes PA was associated with a modest 1-2% lower fall risk, but not fractures. Higher proportions of moderate-to-vigorous intensity PA (MVPA) vs. remaining behaviors were associated with higher compartmental bone microarchitecture and density, and higher muscle power, not strength, in men and women separately. Displacing 10-60 minutes SB for MVPA was consistently associated with higher compartmental bone microarchitecture and density and muscle power.

CONCLUSIONS: Higher proportions of PA, particularly MVPA, may improve clinical outcomes and their risk factors. These results can help guide more effective exercise interventions by ensuring adequate sleep and increasing MVPA at the expense of SB to lower the public health burden of falls and fractures.

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