Protective Effects of Exercise on Cognition and Brain Health in Older Adults

Amanda V. Tyndall; Cameron M. Clark; Todd J. Anderson; David B. Hogan; Michael D. Hill; R.S. Longman; Marc J. Poulin

Disclosures

Exerc Sport Sci Rev. 2018;46(4):215-223. 

In This Article

Abstract and Introduction

Abstract

Accelerated trajectories of cognitive decline in older adults may increase the risk of developing Alzheimer disease and related dementias (ADRD). Physical activity has potential modifying effects on these changes that could prevent or delay ADRD. This review explores the hypothesis that multiple, mutually complimentary, and interacting factors explain the positive association between exercise and the optimization of cognition in older adults.

Introduction

We live in an aging world. It is estimated that by the year 2024, older adults (i.e., those aged 65 years and older) will account for 20.1% of the Canadian population, up from the current 16.1%.[1] Increasing age is strongly associated with the development of dementia, particularly from Alzheimer disease (AD) and other neurodegenerative causes. Dementia is characterized by the presence of significant cognitive decline to the point where independence in everyday activities becomes affected. There are multiple potential causes, with AD the most common. At autopsy, most of those with dementia will have evidence of Alzheimer or vascular pathologies. A more comprehensive understanding of the mechanisms underlying the development of dementia will aid in developing effective interventions to promote healthy brain aging. Even with our current imperfect understanding, there is hope that we can bend the incidence curve and prevent many future cases. The Lancet Commission on dementia recently concluded that up to 35% of all cases may be attributable to nine potentially modifiable risk factors including education, hypertension, obesity, hearing loss, smoking, depression, physical inactivity, social isolation, and diabetes.[2] Because of the frequent synergistic interaction between vascular and Alzheimer pathology in producing the dementia phenotype, it is important to develop a better understanding of the contributions of vascular disease to neurodegenerative causes of dementia.[3]

The World Health Organization has identified physical inactivity as the fourth leading risk factor for mortality. Physical inactivity has been recognized as a modifiable risk factor for cardiovascular disease, type 2 diabetes, and obesity. Successfully promoting increased physical activity, such as by engaging in regular aerobic exercise, has the potential to reduce the number of people who will develop a variety of age-associated diseases.

While the potential beneficial effects of exercise on cognition and brain health in older adults are well established, the mechanisms underlying this association remain incompletely understood. This review will examine the central hypothesis that multiple, mutually complementary and interacting factors are at play to optimize cognition and brain health in older adults (Figure). Furthermore, this review will examine the interplay between these factors and will explore the novel hypothesis that the beneficial effects of exercise on cognition are explained, at least in part, by changes in cerebrovascular function (e.g., basal cerebral blood flow, cerebrovascular reserve). Finally, we will review recent evidence suggesting the existence of a dose-dependent relation between exercise intensity and improved cognition and brain health in older adults.

Figure.

Proposed mechanisms underlying cognitive decline with aging and influence of physical activity on cognitive health. Each box in the top panel represents a broad category of proposed biomarkers, physiological factors, and psychological and lifestyle factors of cognitive aging with the specific subcategories. Each of the subcategories describes with an arrow the association of age with that category. Factors associated with physical activity include adherence to a physical activity program, dose of the activity, type of activity, and social support in the activity. Biomarkers and physiological factors are proposed to be the driving factors that improve brain function through the increase or decrease of the specific subcategory (arrows designate influence of physical activity on the factor). The mechanisms are proposed to influence brain functions and health behaviors including attention, executive function, memory, mood, and sleep. Furthermore, we propose that there is an interplay between these factors that explains the beneficial effects of exercise on cognition. BMI, body mass index; V̇O2max, maximal aerobic capacity; WHR, waist hip ratio.

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