Body-brain Dynamics - An Observational Epidemiological Perspective

Given the significant public health burden caused by brain abnormalities and dementia, there is a great need for identifying intervention strategies to delay the progression of brain abnormalities. Among the interventions tested, non-pharmacological approaches and lifestyle modifications have received great attention. \ud Indeed, the beneficial effects of physical activity on brain and mental health have been well documented. However, it remains unanswered how little and which component of physical activity could boost a change in brain structure and function, especially in adults aged 80 years and older who are at high risk of developing brain abnormalities and dementia. Answering these questions is important because structured aerobic exercise from current physical activity recommendations may not be feasible for older persons living with physical functional limitations and chronic diseases. It needs to be understood whether the positive effects of physical activity on brain health remain independent of health-related conditions. Another important question is which aspect of brain structure would benefit most from physical activity. For instance, brain areas in the frontal lobe are critical for executive function, a capstone for maintaining independence in late life, and the hippocampus is important for memory formation.\ud To answer these questions, I first critically reviewed the literature on the relationship between physical activity, fitness, and brain structure in older adults. Second, I collected objectively measured physical activity data in a group of older adults with existing data on brain structure. I also analyzed existing data on physical activity, fitness, and brain structure obtained by advanced neuroimaging techniques. \ud The public health significance of my dissertation is to provide scientific recommendations of physical activity on preserving brain structural integrity in community-dwelling older adults. In conclusion, being exercise active and higher fitness are associated with greater microstructural integrity localized in the medial temporal lobe, independent of each other and health-related conditions. In a small subset of very old adults, more steps taken and longer duration of physical activity are associated with greater microstructural integrity in the superior longitudinal fasciculus connecting the frontal lobe and the lateral portion of the temporal lobe, independent of physical function and health-related conditions