Dr. Joseph Mercola - Take Control of Your Health Circadian System Disruptions in Sleep Apnea Increase the Risk of Nighttime Cardiac Events
Dec 16, 2025
New research reveals that untreated sleep apnea leads to a significant nighttime decline in blood vessel function, increasing the risk of heart attacks. Arterial dilation drops by 82% at around 3 a.m., suggesting a critical link between the circadian system and cardiovascular health. Interestingly, this impairment continues despite accounting for sleep quality and apnea severity. The findings hint at the need for tailored treatments that optimize medication timing for better vascular protection in sleep apnea patients.
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Nighttime Vascular Trough Around 3 AM
- In moderate to severe obstructive sleep apnea, arterial dilation follows a 24-hour rhythm with a deep trough around 3:00 a.m..
- Arterial dilation dropped about 82% from peak to trough, explaining increased nighttime cardiac events in apnea patients.
Circadian System, Not Behavior, Drives Night Risk
- A time-isolated sleep-lab protocol separated circadian biology from behavior to reveal intrinsic clock effects on vessels.
- The nighttime vascular impairment persisted after adjusting for sleep quality, blood flow, and apnea severity, implicating the circadian system itself.
Endothelium Dysfunction Tied To Clock Gene Disruption
- Flow-mediated dilation was used and normalized to remove blood flow differences, pointing to endothelial dysfunction rather than vessel size change.
- Repeated apnea events likely disrupt clock genes (BMAL1, PER1, CRY2), shifting metabolic and cardiovascular timing.