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