Dose–Response Relationships between Objectively Measured Daily Steps and Mortality among Frail and Nonfrail Older Adults

PURPOSE: Whether the association between objectively assessed physical activity and mortality differs between adults with versus those without frailty is unclear. We investigated this association in community-dwelling older adults. METHODS: This prospective study used the data of 4165 older adults 65 yr or older from the Kyoto–Kameoka study in Japan who wore a triaxial accelerometer (EW-NK52). The number of steps was classified by quartiles using the average daily value of data obtained from the accelerometer across four or more days. Frailty was evaluated using the validated Kihon Checklist. We evaluated the association between mortality and daily steps using a multivariable Cox proportional hazards analysis and restricted spline model. RESULTS: The average daily steps for the first, second, third, and fourth quartiles were 1786, 3030, 4452, and 7502, respectively. In total, 113 deaths were recorded during a median follow-up of 3.38 yr (14,061 person-years). After adjusting for confounders, the top quartile was associated with a lower hazard ratio (HR) for mortality than the bottom quartile (HR = 0.39, 95% confidence interval = 0.18–0.85). In a stratified model by frailty status, the daily step count dose–response curve at which the HR for mortality plateaued among nonfrail individuals was approximately 5000–7000 steps per day. By contrast, the daily step count showed an inverse relationship with mortality at approximately 5000 steps or more per day in frail individuals. CONCLUSIONS: The relationship between daily steps and mortality is different between those with and those without frailty, and people with frailty may require more daily steps than those with nonfrailty to achieve the inverse relationship with mortality. These findings may be useful for informing future physical activity guidelines.