Year of Publication

2017

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Pharmacology and Nutritional Sciences

First Advisor

Dr. D. Travis Thomas

Second Advisor

Dr. Geza Bruckner

Abstract

Muscle health declines with age, influencing both muscle strength and performance. Modifiable lifestyle factors may mitigate muscle dysfunction by altering muscle lipid depots. Vitamin D status, dietary intake, and physical activity each play a role in muscle health during aging. Low vitamin D status (measured as 25(OH)D) is prevalent among older adults and has been associated with functional limitations and impaired physical performance. Previously, 25(OH)D concentrations were inversely associated with extramyocellular lipid (EMCL) and our lab observed a significant positive relationship between 25(OH)D concentrations and IMCL. Studies have shown mixed results regarding the effects dietary fat intake interventions have on muscle lipid depots. It is well established that exercise contributes to improved muscle health, but to date studies have not examined the relationship between daily physical activity levels, muscle lipid depots, and local muscle tissue hemodynamics. We used novel non-invasive technology to measure gastrocnemius muscle lipid depots (Proton Magnetic Resonance Spectroscopy) and monitor local muscle tissue hemodynamics during a foot plantar flexion exercise (Near Infrared/Diffuse Correlation Spectroscopy). The first aim was to further elucidate the relationship between 25(OH)D concentrations, physical function, and muscle lipid depots. We also examined 25(OH)D concentrations and muscle lipid depots differences in older adults with varied body mass index (BMI) and physical activity levels. We observed a negative relationship between 25(OH)D concentrations and EMCL. In females, greater 25(OH)D concentrations and lower EMCL were significant predictors of faster Four Square Step Test times, independent of BMI and age. Greater EMCL and IMCL content were observed with increased BMI, but statistical significance was not reached. The second aim was to retrospectively examine the relationship between dietary fat intake and muscle lipid depots in participants enrolled in a double-blinded placebo-controlled trial. We also investigated the relationship between physical activity levels and local muscle tissue hemodynamics. Increased dietary fat intake ratio of polyunsaturated to saturated fatty acids (PUFA:SFA) and study intervention (7 days of aerobic training) were the best predictors of lower IMCL content, independent of age, BMI, and physical activity. Compared with individuals with lower physical activity levels, individuals that reported greater physical activity had lower relative blood flow and relative oxygen consumption during and after a foot plantar flexion exercise. Together these findings suggest that increased physical activity, consumption of greater PUFA:SFA, and maintenance of sufficient 25(OH)D concentrations may have favorable effects on muscle lipid depots and contribute to the preservation of muscle health.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2017.019

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