Date

June 2012

Document Type

Dissertation

Degree Name

Ph.D.

Institution

Oregon Health & Science University

Abstract

Background Among older adults, lower-extremity functional decline is strongly associated with risk of future disability. Because regular engagement in physical activity is an effective means of slowing functional decline and preserving functional health, characteristics of the neighborhood built environment associated with physical activity among older adults should result in downstream effects on the trajectory of lower extremity functional decline. However, few studies have explored the relationship between neighborhood built environment and the trajectory of lower-extremity functional decline, and none have examined the effect of change in neighborhood built environment over time on physical function among older adults. The purpose of this study was to describe the association of objectively measured characteristics of the neighborhood built environment with the trajectory of lower-extremity function among older women over a 12-year period in Portland, Oregon. Methods This retrospective, cohort study examined the association between objective measures of neighborhood built environment and gait speed, a widely used measure of lower extremity function, among a sample of 1256 community-dwelling older women enrolled in the Portland, Oregon cohort of the Study of Osteoporotic Fractures. Participants‘ baseline visit occurred between 1986 and 1988, and follow-up visits occurred every two years thereafter. Data from participants first six visits, a follow-up period of approximately 12 years, were used in this analysis. Measures of the neighborhood built environment corresponding to the time period of the study were constructed from historical data in the Regional Land Information System and linked to participants‘ residential addresses using geographic information system technology. Measures of public transit accessibility, street connectivity, and land-use mix were combined in an index of neighborhood walkability. Parallel-process, latent growth curve models were constructed to examine the association of baseline neighborhood walkability with baseline gait speed, baseline neighborhood walkability with change in gait speed, and change in neighborhood walkability with change in gait speed. A similar series of models examined the association of distance to parks/green spaces with gait speed. Models were adjusted for age, educational attainment, complex comorbidity, incident fracture, and neighborhood socioeconomic status. A pattern-mixture modeling approach was employed to adjust for attrition. Results Advanced age, lower educational attainment, and the presence of complex comorbidity were all significantly associated with lower gait speed at baseline. Advanced age was associated with greater decline in gait speed over time. After controlling for age, education, complex comorbidity, incident fractures, and neighborhood socioeconomic status, baseline neighborhood walkability was not significantly associated with baseline gait speed or change in gait speed over time. There was, however, a statistically significant association between the slope of neighborhood walkability and the slope of gait speed (b=.024, p=.020). A one-decile increase in walkability over the study period was associated with a .024 m/sec reduction in the rate of gait speed decline. There were no significant associations between neighborhood distance to parks/green space and the trajectory of gait speed. Conclusions This study found that change in neighborhood walkability over time was associated with the degree of change in gait speed over time. Women who lived in neighborhoods that became more walkable over the 12-year study period (i.e. increased access to public transit, more diverse land-use mix, and greater street connectivity) had a reduced rate of gait speed decline. These findings indicate that characteristics of the neighborhood built environment are a modifiable determinant of lower-extremity function among older women, and suggest that efforts to promote pedestrian-friendly urban design may be a valuable means of reducing disability among older adults.

Identifier

doi:10.6083/M4WD3XKZ

School

School of Nursing

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