The effect of aerobic exercise on cerebrovascular function and cognition in older adults

The effect of aerobic exercise on cerebrovascular function and cognition in older adults

Dementia prevalence is expected to treble over the next 30 years. This is only partly explained by the fact that the global population is ageing. Cerebrovascular function and cognitive decline throughout ageing which is exacerbated by reduced cardiometabolic health status, as this promotes chronic low-grade inflammation and oxidative stress, thus impairing endothelial function. This reduces the ability of the cerebrovasculature to respond to the metabolic demands of the brain, as well as maintain the integrity of the blood-brain-barrier, both of which have a substantial impact on cognitive function. Modifiable lifestyle factors, such as physical inactivity, that cause a decline in cardiometabolic health leading to conditions such as obesity, exacerbate these changes beyond those that are associated with normal ageing. A large population of older adults globally are both sedentary and obese thus predisposing them to the development of a neurodegenerative disease, such as dementia. Therefore, it is vital that cost-effective evidence-based strategies are implemented to improve both cerebrovascular function and cognition in order to slow or prevent the normal age-related decline and dementia. The aim of this thesis was to investigate the effects of aerobic exercise training (AT) on cerebrovascular function and cognition in older adults.

The purpose of Chapter 3 was to examine cerebrovascular, cognitive and neuroanatomical adaptations to ageing and the potential benefits of exercise training on these outcomes in adults 50 years or older. Cross-sectional or intervention studies that included exercise (aerobic, resistance or multimodal) and its effect on cerebrovascular function, cognition and neuroanatomical adaptations in this age demographic were systematically searched for, tabulated and described narratively. There were limited studies identified that described effects of resistance exercise training and multimodal training on cerebrovascular function and cognition, while AT was the predominant focus of the studies identified. Collectively, the evidence indicated that exercise irrespective of type could improve cerebrovascular function, cognition and/or neuroplasticity through areas of the brain associated with cognition in adults 50 years or older, irrespective of their health status. It was also determined from this chapter that AT could be a promising and inexpensive strategy in improving overall brain health. However, the effects of AT on both cerebrovascular function and cognition are poorly described, as too is the amount of AT needed to improve both of these functions.

Chapter 4 determined the differences in cerebrovascular and cognitive function between aerobic exercise trained, older adults and sedentary, untrained, older adults. This was achieved by using transcranial Doppler ultrasonography (TCD) to determine the cerebrovascular responsiveness (CVR) to physiological (hypercapnia, 5% carbon dioxide) and cognitive stimuli (battery of individually administered cognitive tests). Anthropometric, cardiovascular, exercise performance, and strength measurements, and a blood collection were used to determine the differences in cardiometabolic health between each group. Correlation analyses were performed to determine if cerebrovascular function and cognition were interrelated. The trained group (n=13) had a higher CVR to hypercapnia (80.3 ± 7.2 vs 35.1 ± 6.7%, P < 0.001), higher CVR to cognitive stimuli (30.1 ± 2.9 vs 17.8 ± 1.4%, P = 0.001) and a higher overall cognitive capacity (117 ± 2 vs 98 ± 4, P < 0.001) than the untrained, sedentary group (n=13). Once these parameters were adjusted for covariates (cardiometabolic markers and education), no statistical difference was observed between the groups. Both CVR to hypercapnia and CVR to cognitive stimuli were positively correlated to cognition, indicating the interrelatedness between cerebrovascular function and cognition in older adults. It was concluded that an interaction between AT, cardiometabolic factors and education may exist that directly influence cerebrovascular function and cognition, whereby AT mediates the improvements in these functions in older adults.

Chapter 5 investigated the effects of 16 weeks AT on cerebrovascular and cognitive function in sedentary, obese, older adults. Participants were randomly assigned to either an AT group (n=14) or control group (n=13). Before and after the intervention, TCD was used to measure the CVR to physiological and cognitive stimuli. Following 16 weeks of AT, CVR to hypercapnia (98.5 ± 10.3% vs 58.0 ± 12.1%, P = 0.021), CVR to cognitive stimuli (25.9 ± 1.7% vs 16.4 ± 1.6%, P < 0.001) and total cognitive capacity (111 ± 4 vs 104 ± 4, P = 0.004) increased in the AT group compared with the control group. A very strong relationship was observed between the number of exercise sessions completed and CVR to cognitive stimuli (r = 0.878, P < 0.001), but not for CVR to hypercapnia (r = 0.246, P = 0.397) or total composite cognitive score (r = 0.213, P = 0.465). Cerebrovascular function and cognition improved following 16 weeks of AT, with CVR to cognitive stimuli dependent on the amount of exercise undertaken.

My thesis concludes that AT has a positive effect on brain health by improving both cerebrovascular function and cognition in older adults, particularly in those who aresedentary, untrained and obese. Further studies are arranted to determine if a minimum dose of AT is required to improve brain health and if the improvements can occur at any age throughout the lifespan.

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