The persistent anxiety that often accompanies aging may finally have a clear neurobiological explanation, offering new therapeutic targets for millions of older adults struggling with emotional regulation. This discovery challenges the assumption that age-related anxiety is simply psychological adjustment to life changes. A carefully controlled study of 61 cognitively healthy adults over 65 revealed that deteriorating slow-wave activity during deep sleep directly predicts next-day anxiety levels. The research tracked participants through polysomnography sleep monitoring followed by structural brain imaging, with a subset monitored for four years longitudinally. The mechanism centers on slow-wave activity—the powerful, synchronized brain oscillations that occur during the deepest phase of non-REM sleep. As key emotion-processing brain regions atrophy with age, they lose capacity to generate the robust slow waves essential for overnight anxiety regulation. Statistical mediation analysis demonstrated that impaired slow-wave activity completely explained the relationship between regional brain atrophy and disrupted emotional processing. This represents a significant advance in sleep neuroscience, connecting three previously separate observations: age-related brain shrinkage, deteriorating sleep architecture, and increased anxiety symptoms. The findings suggest targeted interventions to enhance slow-wave sleep—through techniques like acoustic stimulation, temperature regulation, or pharmacological approaches—could potentially restore emotional stability in aging adults. Unlike anxiety medications that mask symptoms, sleep-based interventions might address the root neurophysiological cause.