Insomnia

Insomnia is a sleep disorder defined by persistent difficulty initiating or maintaining sleep — or non-restorative sleep — despite adequate sleep opportunity, causing clinically meaningful daytime impairment. Per DSM-5 and ICSD-3, chronic insomnia disorder requires symptoms on at least three nights per week for at least three months. Approximately 10% of the adult population meets diagnostic criteria; prevalence rises with age, making it among the most common sleep complaints in older adults. The pathophysiology centers on hyperarousal: sustained activation of the HPA axis and the sympathetic nervous system elevates nighttime cortisol, raises core body temperature, and increases whole-brain glucose metabolism — all antagonizing sleep onset and maintenance. Prospective cohort data raise concern for long-term consequences: a 2019 meta-analysis by Ge et al., pooling 29 cohorts with over 1.5 million participants, found that difficulty initiating sleep and non-restorative sleep were independently associated with elevated all-cause and cardiovascular mortality risk; insomnia disorder as a diagnostic entity and difficulty maintaining sleep did not reach statistical significance. Cognitive behavioral therapy for insomnia (CBT-I) — combining sleep restriction, stimulus control, cognitive restructuring, and sleep-hygiene education — is the first-line treatment per the 2016 American College of Physicians guideline; pharmacotherapy is adjunctive and carries greater risk in older populations.