Circadian System Disruptions in Sleep Apnea Increase the Risk of Nighttime Cardiac Events

New research shows that people with untreated sleep apnea experience a sharp nighttime drop in blood vessel function driven by the circadian system, increasing vulnerability to heart attacks and other cardiac events In a tightly controlled sleep-lab study, participants' arteries showed their worst ability to dilate around 3:00 a.m., revealing an 82% decline in vascular function during the biological night This impairment persisted even after adjusting for blood flow, sleep quality, and apnea severity, confirming the circadian system — not behavior or breathing events — directly weakens vascular health at night The findings help explain why people with sleep apnea experience more nighttime cardiac events, contrasting with the general population's morning peak in heart attacks and sudden cardiac death Researchers emphasize that understanding circadian timing may help refine cardiovascular treatments for sleep apnea patients, including optimizing medication schedules to enhance nighttime vascular protection