Mild Cognitive Impairment Is Associated With Markers of Muscle Weakness and Reduced Bone Density, and Specific Metabolic Alterations Despite Preserved Physical Activity

OBJECTIVES: Bone loss and frailty commonly occur in people with dementia residing in nursing homes and lead to increased risk of disabilities and poor health outcomes. Whether these systemic manifestations and related metabolic disturbances are present in older adults with Mild Cognitive impairment (MCI), who are still physically active, remains unclear. METHODS: Community dwelling older adults without confounding comorbidities were divided, using the Montreal Cognitive Assessment (MoCA) score cut-off of 26, into two groups: non-MCI (n = 18; age: 67.3 [63.3, 71.2 y]) and MCI (n = 20; age: 71.3 [66.9, 75.7 y]). Body composition (by DXA), respiratory strength (by mouth pressure), and extremity strength (by dynamometer) were assessed. Stable isotope techniques were used to measure production and plasma concentrations of amino acids involved in muscle, bone, and brain health (tau-methylhistidine, hydroxyproline, glycine, tryptophan). Plasma enrichments were analyzed by LC-MS/MS. Statistics performed by ANCOVA with age, gender, and BMI as covariates. Significance set at P < 0.05. Results expressed as means [95% CI]. RESULTS: MCI participants (MoCA score: 22.5 [21.3, 23.6]) had lower respiratory muscle strength (p = 0.007) than the non-MCI group (MoCA score: 28.2 [27.5, 28.8]) but muscle mass and daily physical activity were not different. Bone density of the spine (p = 0.02) and hip (p = 0.07) were lowest in those with the lowest MoCA scores. The MCI group had lower concentrations of glycine (p = 0.0045), tryptophan corrected for large neutral amino acids (p = 0.0017), and productions of glycine (p = 0.0085), tau-methylhistidine (p = 0.05), and tryptophan (p = 0.06). MoCA score was negatively associated with plasma triglyceride (p = 0.02) and liver enzyme (AST) level (p = 0.01), but not with glucose or CRP levels. CONCLUSIONS: Older adults with MCI are prone to low bone density and respiratory muscle weakness despite preserved physical activity. Whether these systemic manifestations are causally related to the observed metabolic alterations in MCI deserves further investigation. FUNDING SOURCES: None