Presence of chronic morbidities alters skeletal muscle health and amino acid kinetics in mild cognitive impairment

BackgroundSkeletal muscle weakness and mild cognitive impairment (MCI) commonly occur with aging.ObjectiveWe examined whether presence of chronic morbidities in MCI is associated with specific alterations in muscle health, functional capacity, and whole body amino acid kinetics.MethodsA group of 247 older adults were stratified into MCI/non-MCI (Montreal Cognitive Assessment) and presence/absence of chronic diseases. We measured lean mass by dual-energy x-ray absorptiometry, strength by dynamometry, and functional capacity by 6-min walk test. Postabsorptive whole body production (WBP) of amino acids were assessed by pulse administration of a mixture of 18 amino acid stable isotopes.ResultsMCI was associated with lower lean mass, functional capacity (p < 0.003), and WBP of arginine, glycine, leucine, and phenylalanine to tyrosine conversion (reflecting net protein breakdown (net PB)) but higher WBP of taurine (all p < 0.05). Presence of chronic morbidities was associated with lower muscle strength, WBP of glycine, and net PB (p < 0.0001), but higher WBP of phenylalanine, glutamate, taurine, tryptophan, and leucine (all p < 0.05). MCI*chronic morbidity interactions were found for muscle strength and net PB (p < 0.0001), with the lowest values in MCI with chronic morbidities.ConclusionsPresence of MCI and chronic morbidities in the older population affect different markers of muscle health and functional decline. Individuals with both MCI and chronic morbidities are at increased risk for severe muscle weakness likely related to a severe downregulation of glycine production and net protein breakdown. Therefore, it is important to consider the presence of chronic morbidities when investigating muscle health and functional capacity in MCI.