Dose-Response Relationship Between Life-Space Mobility and Mortality in Older Japanese Adults: A Prospective Cohort Study

OBJECTIVES: Some epidemiological studies of older American adults have reported a relationship between life-space mobility (LSM) and mortality. However, these studies did not show a dose-response relationship and did not include individuals from other countries. Therefore, we evaluated the dose-response relationship between LSM and mortality in older adults. DESIGN: Prospective cohort study. SETTING AND PARTICIPANTS: We used the data of 10,014 older Japanese adults (aged ≥65 years) who provided valid responses to the Life-Space Assessment (LSA) in the Kyoto-Kameoka study in Japan. METHODS: LSM was evaluated using the self-administered LSA consisting of 5 items regarding life-space from person's bedroom to outside town. The LSM score was calculated by multiplying life-space level by frequency score by independence score, yielding a possible range of 0 (constricted life-space) to 120 (broad life-space). These scores were categorized into quartiles (Qs). Mortality data were collected from July 30, 2011 to November 30, 2016. A multivariate Cox proportional hazards model that included baseline covariates were used to evaluate the relationship between LSM score and mortality risk. RESULTS: A total of 1030 deaths were recorded during the median follow-up period of 5.3 years. We found a negative association between LSM score and overall mortality even after adjusting for confounders [Q1: reference; Q2: hazard ratio (HR) 0.81, 95% CI 0.69-0.95; Q3: HR 0.70, 95% CI 0.59-0.85; Q4: HR 0.68, 95% CI 0.55-0.84, P for trend < .001]. Similar results were observed for the spline model; up to a score of 60 points, LSM showed a strong dose-dependent negative association with mortality, but no significant differences were observed thereafter (L-shaped relationship). CONCLUSIONS AND IMPLICATIONS: Our findings demonstrate an L-shaped relationship between LSM and mortality. This study will be useful in establishing target values for expanding the range of mobility among withdrawn older adults with a constricted life-space.