Cross-sectional association between physical activity level and subjective cognitive decline among US adults aged ≥45 years, 2015

Highlights

• Physical activity may help reduce the risk of subjective cognitive decline (SCD).

• Among US adults, prevalence of SCD increased as physical activity level decreased.

• 1 in 11 active adults (8.8%) report SCD, compared to 1 in 6 inactive adults (15.7%).

• Among those with SCD, functional limitations were more common among inactive adults.

• Promoting physical activity may help optimize cognitive health in the US.

Abstract

Subjective cognitive decline (SCD) is the self-reported experience of worsening or more frequent confusion or memory loss within the previous 12 months and can be one of the earliest symptoms of Alzheimer's disease. Regular physical activity can contribute to the primary, secondary, and tertiary prevention of cognitive decline. At the national level, prevalence estimates of SCD by physical activity level in the United States are currently unknown. The purpose of this study is to examine the prevalence of SCD and resulting functional limitations by physical activity level among US adults aged ≥45 years. Data from 33 states and the District of Columbia participating in the 2015 Behavioral Risk Factor Surveillance System (N = 128,925) were analyzed. We estimated the prevalence of SCD (a positive response to a question about worsening or more frequent confusion or memory loss within the previous 12 months) and resulting functional limitations overall and by self-reported physical activity level based on current guidelines (i.e., active, insufficiently active, and inactive). Odds ratios were estimated using logistic regression models adjusting for respondent characteristics. Overall, 11.3% of US adults aged ≥45 years reported SCD. Prevalence of SCD increased as physical activity level decreased (active: 8.8%; insufficiently active: 11.4%; inactive: 15.7%). Among those with SCD, the prevalence of functional limitations also increased as physical activity level decreased (active: 40.5%; insufficiently active: 50.0%; inactive: 57.4%). These differences largely remained after adjusting for respondent characteristics. Findings highlight the potential public health impact nationally of efforts to promote physical activity for cognitive health.

Introduction

An estimated 11.2% of US adults aged ≥45 years have subjective cognitive decline (SCD), which is the self-reported experience of worsening or more frequent confusion or memory loss within the previous 12 months (Taylor et al., 2018; Alzheimer's Association, 2018; Reid and Maclullich, 2006). SCD can be one of the earliest noticeable symptoms of Alzheimer's disease (Alzheimer's), a fatal form of dementia (Alzheimer's Association, 2018). Although not everyone who reports SCD goes on to develop dementia, previous studies suggest that half of older adults with subjective memory complaints develop more severe cognitive decline (Alzheimer's Association, 2018; Kaup et al., 2015; Centers for Disease Control and Prevention, 2013). In addition, regardless of progression to more severe cognitive impairment, SCD can result in limitations to an individual's ability for self-care (Taylor et al., 2018; Centers for Disease Control and Prevention, 2013). Such functional limitations can include an inability to perform activities important to daily living or to socialize (Taylor et al., 2018; Centers for Disease Control and Prevention, 2013).

Regular physical activity can contribute to the primary, secondary, and tertiary prevention of cognitive decline and dementia (Alzheimer's Association, 2018; 2018 Physical Activity Guidelines Advisory Committee, 2018; Baumgart et al., 2015). Recognizing the importance of physical activity for promoting cognitive health, the Alzheimer's Association includes physical activity as one of “10 ways to love your brain” (Alzheimer's Association, 2019). In addition, an objective of Healthy People 2020 is to increase the proportion of older adults with reduced physical or cognitive function who engage in light, moderate, or vigorous leisure-time physical activities (HealthyPeople.gov, 2019). The Physical Activity Guidelines for Americans, second edition (Guidelines), suggests that regular physical activity can help improve cognition and reduce the risk of dementia (U.S. Department of Health and Human Services, 2018). The Guidelines recommend that adults with chronic conditions be physically active on a regular basis: adults with chronic conditions who are able should do at least 150 to 300 min of moderate-intensity aerobic physical activity a week or 75 to 150 min of vigorous-intensity activity or an equivalent combination of both (U.S. Department of Health and Human Services, 2018). The review of scientific evidence supporting the Guidelines found strong evidence demonstrating that greater amounts of physical activity can help reduce the risk of cognitive impairment and moderate evidence indicating that moderate-to-vigorous physical activity can have beneficial effects on cognition in individuals with diseases or disorders that impair cognitive function (2018 Physical Activity Guidelines Advisory Committee, 2018; Erickson et al., 2019).

The positive association between physical activity and improved cognitive functioning is well established in the literature, resulting in key guidelines recommending physical activity for cognitive health (2018 Physical Activity Guidelines Advisory Committee, 2018; Erickson et al., 2019). However, these studies have largely been conducted either among prospective cohorts or as part of randomized controlled trials (Erickson et al., 2019; Sofi et al., 2011; Beckett et al., 2015; Colcombe and Kramer, 2003; Roig et al., 2013; Smith et al., 2010; Groot et al., 2016; Zheng et al., 2016). To our knowledge the magnitude of this important public health issue at a national level is currently unknown. National estimates of the prevalence of SCD and resulting functional limitations by physical activity level in the United States can help highlight the potential public health impact of promoting physical activity for cognitive health, including preventing cognitive decline and its progression to more severe outcomes including functional limitations. Therefore, the objectives of this study were twofold. First, to assess differences in the prevalence of SCD and resulting functional limitations by physical activity level among US adults aged ≥45 years. Second, to examine the association between physical activity levels and select demographic characteristics with (1) SCD among US adults aged ≥45 years and (2) functional limitations among those with SCD. These findings can be used to identify opportunities to promote physical activity in the United States to help reduce the risk of cognitive decline, and slow its progression among individuals exhibiting this early indicator of poor cognitive health.