The Mean and Variability of Morning Hour Activity Over 2-3 Days Predict 5-Year Mortality and Frailty Risk in a National Sample of Older Adults.

Background

Activity pattern features measured by continuous accelerometry are strongly associated with frailty, making accelerometry a promising, scalable screening tool for frailty. However, adherence to typical 5-7 day wear protocols decreases with age, reducing feasibility. Whether accelerometry measures collected over shorter wear periods predict frailty decline is unknown. In cross-section, we have shown that frailty is most strongly differentiated by morning activity patterns.

Objective

The objective of this study was to determine whether two morning activity measures, mean hourly activity and within activity variance, measured over 72 h predicted 5-year mortality and frailty progression among survivors.

Methods

We conducted a secondary data analysis of the 2010-2011 accelerometry substudy and 2015-2016 data of the National Social Life, Health and Aging Project which included n = 584 community-dwelling older adults; n = 104 died at 5 years. Wrist accelerometers were worn for 72 h in 2010-2011, and an adapted frailty phenotype was measured in both years. We employed a mixed effects location scale model to calculate mean morning (7:00-11:59 am) hourly activity (counts per minute z-score) and within-subject morning hourly activity variance (z-score) for each participant, adjusted for day of week and month of wear. Second, 5-year mortality (logistic) and adapted frailty phenotype scores (range 0-4, ordinal) were regressed on baseline frailty and both accelerometry z-scores in a 2-stage model, adjusting for covariates.

Results

After adjusting for baseline frailty, demographics, comorbidities, BMI, and cognition, higher mean morning hourly activity predicted lower 5-year mortality risk (OR = 0.64 for 1 SD increase, p = 0.04). Conversely, higher morning activity WS variance predicted better frailty scores among survivors (OR = 0.67 for 1 SD increase, p = 0.01).

Conclusions

Higher activity levels and higher day-to-day morning activity variance measured over just two to three mornings differentiate those at higher risk of death and frailty decline, increasing the feasibility of using accelerometry as a digital frailty screening tool.