Cardiorespiratory fitness (CRF) is a well known important predictor of cardiovascular disease and overall mortality. CRF is of interest as a factor that could be intervened upon to promote health given it can be modified mainly through exercise. However, whether CRF is associated with cognitive function, brain magnetic resonance image (MRI) findings, and overall Health-related quality of life (HRQOL) in middle-aged adults is unknown. The first manuscript tested the hypothesis that greater CRF was associated with better cognitive function 25 years later using data from the community-based Coronary Artery Risk Development in Young Adults (CARDIA) study of black and white men and women aged 18-30 at recruitment in 1985-86 (year 0). Per minute of maximal treadmill duration (Maxdur) of a symptom-limited treadmill test , the Rey Auditory-Verbal Learning Test (measuring verbal memory) was 0.12 words recalled higher (P<0.0001), the Digit Symbol Substitution Test (measuring psychomotor speed) was 0.92 digits higher (P<0.0001), and the Stroop Test score (measuring executive function) was 0.52 lower (better performance, P<0.0001). So, better cognitive function at ages 43-55 years was clearly associated with better CRF 25 years earlier.
The second manuscript evaluated the hypothesis that greater CRF is associated with lower odds of having unfavorable brain MRI findings. In the CARDIA study, the odds ratio (OR) for having less whole brain volume was 0.82 per minute higher Maxdur (P=0.002) and for having low white matter integrity was 0.85 (P=0.03). No significant associations were observed between Maxdur and normal and abnormal white matter tissue volume. Therefore, greater CRF was associated with less brain atrophy and greater white matter integrity measured 5 years later.
The third manuscript examined the hypothesis that CRF is associated with mental and physical HRQOL and individual questions contributing to the HRQOL scores. In the CARDIA study, Maxdur was inversely associated with low HRQOL at year 25 with the OR for having low Mental Component Summary score (<1SD below the average in the general U.S. population) of 0.88 per minute higher of Maxdur (P<0.0001) and the OR for having low Physical Component Summary score of 0.69 (P<0.0001). High Maxdur was related to each but one individual question contributing to the HRQOL.
The projects in this dissertation support the hypothesis that CRF is associated with cognitive function, brain atrophy, white matter integrity and HRQOL, which make it possible to better identify individuals at risk for these conditions at young to middle adulthood and further suggest ways to prevent deterioration of cognition, brain structure and function, and HRQOL later in life. The findings in this project contribute evidence to the impact of CRF on brain aging and overall health in middle aged adults.
University of Minnesota Ph.D. dissertation. June 2013. Major: Epidemiology. Advisor: David R. Jacobs, Jr. 1 computer file (PDF);) x, 124 pages.
Cardiorespiratory fitness in relation to cognitive function, brain MRI measures, and quality of life in middle-aged population.
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