Accelerometer-measured daily steps and subjective cognitive ability in older adults: A two-year follow-up study

https://doi.org/10.1016/j.exger.2020.110874Get rights and content

Highlights

  • More daily steps were linearly related to a reduced rate of subjective cognitive decline.

  • 3500–6999 steps/day was related to an approximate reduction of 40% in the rate of subjective cognitive decline.

  • 7000 steps/day was related to an approximate reduction of 60% in the rate of subjective cognitive decline.

Abstract

There is still a paucity of longitudinal studies examining the relationships between objectively-assessed daily steps and cognitive performance in older adults. The current study aimed to explore whether there is a dose-response relationship between accelerometer-measured daily steps and subjective cognitive decline rate after 2 years in older adults. A total of 285 community-dwelling older adults (age = 74.52 ± 6.12 years, female = 55.4%) wore accelerometers for 7 consecutive days measuring daily steps in 2012. Subjective cognitive ability was measured using a Chinese version of the Ascertain Dementia 8-item Questionnaire (AD8). In total 274 (96.1%) participants completed the follow-up study in 2014. Multivariable negative binomial regression adjusted for confounders was undertaken. Daily steps were linearly related to a reduced decline rate in subjective cognitive ability after 2 years. When daily steps were categorized into groups (<3500, 3500–6999, and ≥7000 steps/day), taking approximately 3500–6999 steps/day was associated with a reduced subjective cognitive decline rate (RR = 0.57, 95% CI = 0.37–0.89) after 2 years compared with <3500 steps/day. When accruing ≥7000 steps/day, the decline rate progressively decreased further (RR = 0.43, 95% CI = 0.23–0.82). Sensitivity analyses supported the stability of these findings. These results suggest that there is an inverse dose-response association of daily steps with subjective cognitive decline rate. Even as few as 3500–6999 steps/day was associated with a lower subjective cognitive decline rate after 2 years. Accumulating ≥7000 steps/day could provide greater protection for subjective cognitive ability.

Introduction

Subjective cognitive decline in later life is a serious public health concern. Subjective cognitive decline refers to the self-reported perception of worsening cognitive abilities (e.g., memory loss) (Centers for Disease Control and Prevention, 2020) and has been recognized as a marker future cognitive impairment (Jessen et al., 2014). According to the Alzheimer's Association, the annual costs of cognitive decline for Americans aged over 65 years in 2019 is $290 billion; these costs are projected to increase by more than $1.1 trillion in 2050 (Alzheimer's Association, 2019). Older adults with cognitive decline including Alzheimer's disease are at greater risk of independence loss, low quality of life, and premature mortality compared with those who are cognitively intact (Fiest et al., 2016). Given the potential impact of deleterious health consequences and healthcare expenditure caused by cognitive decline, it is vital to identify the underlying factors for protecting older adults' cognitive health.

A physically active lifestyle has demonstrable benefits on older adults' health outcomes, including cognitive functioning (Ku et al., 2016; Murphy et al., 2018; UK Chief Medical Officers, 2019; U.S. Department of Health and Human Services, 2018). In particular, walking is the most common daily activity contributing to a physically active lifestyle among older adults (Rafferty et al., 2002). In general, older adults take between 2000 and 9000 steps a day; the broad range reflecting the natural diversity of physical function (Tudor-Locke et al., 2011) as well as various motivational factors (e.g., personality traits) (Sutin et al., 2016) in older adults.

A physical activity goal of 10,000 steps per day is often encouraged (Torjesen, 2018). However, there has been little evidence to support the goal of 10,000 steps per day for improving older adults' health outcomes. For example, one review demonstrated that direct estimates of minimal amounts of free-living moderate-to-vigorous physical activity are approximately 7000–8000 steps a day, suggesting that this may be a reasonable threshold of free-living physical activity that is also associated with current public health guidelines (i.e. 150 min of MVPA a week) (Tudor-Locke et al., 2011). More recently, findings from a 3-year follow-up study of 16,741 women with a mean age of 72 years revealed a reduction in mortality rates in association with a higher number of steps accrued up to approximately 7500 steps per day, above which the rates plateaued (Lee et al., 2019). These findings suggest that 7000–8000 steps a day could yield health benefits.

To date, there is only one study showing that pedometer-assessed daily steps are positively associated with aspects of cognitive ability (e.g., executive functioning and attention) in older age (Calamia et al., 2018). Although the study found positive associations between accumulated steps and older adults' cognitive abilities, there are gaps in the literature that calls for more research. First, it is a cross-sectional study, which cannot establish causal temporality between daily steps and cognitive ability in older adults. Second, although pedometers are often utilized in daily steps measurement, uni-axial pedometers are less sensitive to detect movements than tri-axial accelerometry, and are especially prone to underestimating step counts (Dijkstra et al., 2008). Third, it is important to consider the device wear time as a covariate for examining the relations between objectively-assessed physical activity parameters and health outcomes (Ku et al., 2019) because failure to take absolute wear time into account means that estimates of daily steps may vary according to the duration of objective recordings. Finally, the dose-response association of daily steps and cognitive ability in older adults remains unclear; there is limited evidence on the number of daily steps needed to have a protective influence on future cognitive decline. Understanding if there is a dose-response relationship based on daily steps is crucial for clinical practitioners and public health guideline.

To fill these gaps in the literature, the current study aimed to examine the dose-response relationships between accelerometer-measured daily steps and subjective cognitive ability among community-dwelling older adults over a 2-year follow-up period. We also included underlying factors in multivariable analyses for adjustment and performed sensitivity analyses to test for confounding and reverse causation.

Section snippets

Sample and study design

The is a two-year longitudinal study of a community-based project in Hunei District, Kaohsiung, the second largest city in Taiwan. The first wave of measures (baseline) was conducted between August and October 2012. Participants in the current study were recruited via quota sampling (national distribution of population according to gender and age in 2011) (Taiwan Ministry of Interior, 2017). Of the 14 villages in the district, approximately 20 participants were recruited from each community

Characteristics

Group differences in subjective cognitive ability at follow-up categorized by baseline descriptive statistics of participants are presented in Table 1. Participants were more likely to have lower subjective cognitive ability at follow-up if they were female, older, unmarried, had lower educational levels, lower daily steps, greater ST, engaged in MVPA <150 min a week, had more chronic diseases, had depressive symptoms, and experienced difficulty in activities at baseline (all p-values <0.05).

Discussion

This prospective cohort study investigated the dose-response associations between accelerometer-assessed daily steps and subjective cognitive ability in community-dwelling older adults over a two-year follow-up. Our findings suggested that more daily steps taken in free-living conditions were linearly associated with a reduced subjective cognitive decline rate. When daily steps were further categorized into three levels (<3500, 3500–6999, and ≥7000 steps per day), older adults who averaged

Conclusions

In sum, this study expands our understanding of the dose-response associations between accelerometer-assessed daily steps taken in free-living condition and subjective cognitive ability in community-dwelling older adults. It presents evidence that even as few as 3500–6999 steps/day at baseline was more likely to have lower subjective cognitive decline rate over a two-year follow-up. When at least 7000 daily steps were accumulated, the rate progressively decreased further. This extends the

Funding

This work was partly supported by the Ministry of Science and Technology of Taiwan (MOST 104-2410-H-018-028 and MOST 108-2811-H-018-500).

CRediT authorship contribution statement

Shang-Ti Chen:Conceptualization, Writing - original draft, Writing - review & editing, Visualization. Clare Stevinson: Formal analysis, Writing - review & editing, Writing - original draft. Tian Tian: Conceptualization, Writing - original draft, Methodology. Li-Jung Chen: Conceptualization, Data curation, Investigation, Writing - original draft. Po-Wen Ku: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Writing - original draft, Writing -

Declaration of competing interest

The authors declare that they have no conflict of interest.

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