Wrist Accelerometry in the Health, Functional, and Social Assessment of Older Adults

To the Editor: The importance of accelerometry as an indicator of older adult health is increasingly recognized. Low physical activity as assessed using hip accelerometry is associated with disability, cardiovascular risk, and poor health outcomes. Hip accelerometry is considered to be a more-precise measure of activity and sedentary behavior than wrist accelerometry,1 but wrist accelerometers have become ubiquitous commercially and are being used increasingly in research as a result of new activity monitor protocols (e.g., National Health and Nutrition Examination Study). Data relating wrist accelerometry to older adult health is lacking. The objective of the current analysis was to associate wrist accelerometry with an extensive set of health outcomes essential to older adult well-being in a nationally representative community sample. Data from a wrist accelerometry substudy (n = 738) in Wave 2 of the National Social Life, Health, and Aging Project (NSHAP) were analyzed.2 An accelerometer (ActiWatch Spectrum, Philips Respironics, Aurora, IL) worn on the nondominant wrist continuously measured activity and sleep over 72 hours (not removed for water activities).3 Activity counts were recorded every 15 seconds (epoch). A galvanic sensor excluded nonwear time. Wake time was determined using software protocols and investigator adjustment to align event markers, ambient light, and activity data.4 Only days with 10 hours or more of wake time were included. Average daily activity was calculated as the sum of wake time counts divided by total number of epochs. Valid hours worn, number of weekend days worn (categorical, reference: no weekend days), and month of wear (categorical, reference: January) to approximate season were calculated. Self-rated physical and mental health (excellent, very good, good, fair, poor) were assessed. Systolic and diastolic blood pressure, nonfasting glycosylated hemoglobin (%), C-reactive protein (CRP, mg/L), and body mass index (BMI, kg/m2) were measured.2 Obesity was identified as BMI of 30 kg/m2 or greater. Participants reported any diagnoses of heart problems; diabetes mellitus; stroke; cancer (other than skin); or asthma, chronic obstructive pulmonary disease, or emphysema5 and performed a 3-m timed walk twice and five timed serial chair stands.3 The fastest walk and chair stands times were recorded. Difficulty performing any activity of daily living (ADL) or instrumental activity of daily living (IADL) was self-reported.3 Frequency of 11 depressive symptoms and seven anxiety symptoms during the past week,6 frequency of attending meetings of organized groups and socializing with friends or family at least once per month, and current alcohol or tobacco use were self-reported. Age at the time of survey, sex, education, race, Hispanic ethnicity, household assets, and current working status were self-reported. Cognitive function was determined using the survey-adapted Montreal Cognitive Assessment.7 Association between average daily activity and each outcome was assessed using survey-adjusted regression models controlling for covariates, wear time, weekend days, and wear month. Effects per 10 activity counts are reported. Analyses were conducted using Stata version 14 (Stata Corp., College Station, TX). Of 738 participants, 631 had complete accelerometer and covariate data. Age ranged from 71.2 to 72.4, 52.8% were female, and 83.6% were white. Average daytime activity count was 54.2 (95% confidence interval (CI) = 52.1–56.4), mean number of valid wake hours was 36.4 (95% CI = 35.4–37.3), and 59.6% of participants did not wear the accelerometer on a weekend day (95% CI = 55.6–63.4%). Multivariate regression models demonstrated that all relationships between accelerometry and health outcome were in the expected direction (Tables 1 and 2). More physical activity was significantly associated with better reported physical (P < .001) and mental (P = .009) health, lower diastolic blood pressure (P = .01), lower BMI (P < .001), lower CRP (P = .02), less obesity (P < .001), lower HbA1c (P = .01), fewer reported heart problems (P = .01), less diabetes mellitus (P < .001), faster 3-m walk (P < 0.001), faster chair stands (P = .002), and less reported ADL (P = .002) and IADL (P = .006) difficulty. For example, a 10-point increase in mean activity count was associated with a 0.98-second (=e−0.02) faster walk and 20% lower risk of reporting an ADL disability. Similar to hip devices, wrist accelerometry-measured average daily activity was significantly associated with many physical and functional older adult health outcomes but with few mental health and social engagement outcomes. To the knowledge of the authors, this is the first report showing significant associations between wrist accelerometry and a wide range of health outcomes in a nationally representative sample of older adults.8 Accelerometry was assessed over 3 days, and the findings of strong associations with this brief wear duration suggest that accelerometry may be feasible in clinic settings. Longer durations (e.g., ≥5 days9) may more fully represent habitual activity, increase reliability, and therefore strengthen the accelerometry associations found with health outcomes. With newer wrist devices and algorithms for interpreting output, ease of wear, and low battery requirements, wrist accelerometers may become clinically useful moving forward. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. This work was supported by National Institute on Aging Grants 1R01AG033903–01, R01 AG030481–01A1, and R37 AG030481. Author Contributions: Huisingh-Scheetz: concept, design, analysis, interpretation, drafting, revising, writing, approval of final draft. Kocherginsky: concept, design, analysis, revising, approval of final draft. Dugas: interpretation, revising, approval of final draft. Payne: acquisition of data, revising, approval of final draft. Dale, Conroy: concept, revising, approval of final draft. Waite: concept, design, interpretation of data, revising, approval of final draft. Sponsor's Role: None.

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