Sleep-related Alzheimer's disease vulnerability in aging: A muscle-metabolic perspective

Sleep disruption is a hallmark of aging and a plausible driver of Alzheimer's disease vulnerability. Reduced slow-wave sleep, increased fragmentation, and circadian instability may facilitate amyloid-β accumulation, tau propagation, neuroinflammation, oxidative stress, and impaired glymphatic clearance. Yet the physiological factors that predispose older adults to unstable sleep remain insufficiently integrated into models of brain aging. This Review advances a sleep-muscle-brain framework in which sarcopenia, sarcopenic obesity, and insulin resistance are conceptualized as modifiable muscle-metabolic conditions that may bias sleep continuity and shape the biological impact of sleep disruption. We examine irisin/FNDC5-BDNF signaling as a hypothesis-generating candidate modifier of metabolic regulation, neurotrophic support, and brain resilience, while emphasizing that direct evidence for a causal role in human sleep regulation remains insufficient. Irisin-related pathways intersect with insulin sensitivity, inflammatory control, and BDNF-dependent synaptic plasticity, all of which are relevant to the physiological context in which sleep disruption may influence Alzheimer's disease pathophysiology. We propose that age-related attenuation of muscle endocrine signaling, together with insulin resistance and low-grade inflammation, may lower the threshold at which sleep fragmentation translates into amyloid/tau dyshomeostasis, glial activation, and network dysfunction. Rather than treating sleep disturbance as an isolated brain-centered risk factor, this framework positions sleep as a biobehavioral hub through which peripheral aging processes can modulate neurodegenerative resilience. The Review integrates evidence from sleep neuroscience, geroscience, metabolism, and neurodegeneration, and identifies experimentally testable predictions. A sleep-muscle-brain perspective may help refine risk stratification and guide multimodal interventions combining sleep optimization, resistance exercise, metabolic targeting, and Alzheimer's disease biomarker monitoring.