THE RELATIONSHIP BETWEEN MODIFIABLE LIFESTYLE FACTORS AND MUSCLE LIPID DEPOTS IN OLDER ADULTS

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

Local In Vivo measures of Muscle Lipid and Oxygen Consumption Change in Response to Combined Vitamin D Repletion and Aerobic Training in Older Adults

Intramyocellular (IMCL), extramyocellular lipid (EMCL), and vitamin D deficiency are associated with muscle metabolic dysfunction. This study compared the change in [IMCL]:[EMCL] following the combined treatment of vitamin D and aerobic training (DAT) compared with vitamin D (D), aerobic training (AT), and control (CTL). Male and female subjects aged 60–80 years with a BMI ranging from 18.5–34.9 and vitamin D status of ≤ 32 ng/mL (25(OH)D) were recruited to randomized, prospective clinical trial double-blinded for supplement with a 2 × 2 factorial design. Cholecalciferol (Vitamin D3) (10,000 IU × 5 days/week) or placebo was provided for 13 weeks and treadmill aerobic training during week 13. Gastrocnemius IMCL and EMCL were measured with magnetic resonance spectroscopy (MRS) and MRI. Hybrid near-infrared diffuse correlation spectroscopy measured hemodynamics. Group differences in IMCL were observed when controlling for baseline IMCL (p = 0.049). DAT was the only group to reduce IMCL from baseline, while a mean increase was observed in all other groups combined (p = 0.008). IMCL reduction and the corresponding increase in rVO2 at study end (p = 0.011) were unique to DAT. Vitamin D, when combined with exercise, may potentiate the metabolic benefits of exercise by reducing IMCL and increasing tissue-level VO2 in healthy, older adults

Local In Vivo Measures of Muscle Lipid and Oxygen Consumption Change in Response to Combined Vitamin D Repletion and Aerobic Training in Older Adults

Intramyocellular (IMCL), extramyocellular lipid (EMCL), and vitamin D deficiency are associated with muscle metabolic dysfunction. This study compared the change in [IMCL]:[EMCL] following the combined treatment of vitamin D and aerobic training (DAT) compared with vitamin D (D), aerobic training (AT), and control (CTL). Male and female subjects aged 60−80 years with a BMI ranging from 18.5−34.9 and vitamin D status of ≤32 ng/mL (25(OH)D) were recruited to randomized, prospective clinical trial double-blinded for supplement with a 2 × 2 factorial design. Cholecalciferol (Vitamin D3) (10,000 IU × 5 days/week) or placebo was provided for 13 weeks and treadmill aerobic training during week 13. Gastrocnemius IMCL and EMCL were measured with magnetic resonance spectroscopy (MRS) and MRI. Hybrid near-infrared diffuse correlation spectroscopy measured hemodynamics. Group differences in IMCL were observed when controlling for baseline IMCL (p = 0.049). DAT was the only group to reduce IMCL from baseline, while a mean increase was observed in all other groups combined (p = 0.008). IMCL reduction and the corresponding increase in rVO2 at study end (p = 0.011) were unique to DAT. Vitamin D, when combined with exercise, may potentiate the metabolic benefits of exercise by reducing IMCL and increasing tissue-level VO2 in healthy, older adults