From the Research
Most thrombotic strokes occur in the early morning hours, between 3 AM and 6 AM, due to physiological changes that happen during sleep, as supported by a study published in 2005 1. The study found that the greatest portion of strokes (32.5%) occurred between 03:00 and 06:00 a.m., with nearly one half of the strokes occurring in the very early- to mid-morning hours. Some key factors that contribute to the increased risk of thrombotic strokes during these hours include:
- Increased platelet aggregation and blood viscosity in the early morning, making blood more prone to clotting
- Sympathetic nervous system activation, leading to surges in catecholamines like epinephrine and norepinephrine, which can trigger vasoconstriction and further increase blood pressure
- Low fibrinolysis activity, creating an environment where clots are more likely to form and less likely to be broken down
- Dehydration that occurs during sleep, which can further concentrate blood components and increase stroke risk
- Repeated oxygen desaturation events throughout the night in individuals with sleep apnea, which can damage blood vessels and promote clotting These combined factors create a "perfect storm" for thrombotic events in the predawn hours, particularly in individuals with underlying vascular risk factors, as discussed in a study published in 2020 2. It's also worth noting that hypertension is a major risk factor for stroke, and the prothrombotic state associated with hypertension can be reversed to some extent by antihypertensive treatment, as mentioned in a study published in 2003 3. However, the exact mechanisms underlying the increased risk of thrombotic strokes in the early morning hours are complex and multifactorial, involving various physiological and pathological processes, as discussed in studies published in 2010 4 and 2020 5.