Heart attack, stroke, aortic aneurysm, heart failure and other circulatory problems are more common during the early hours of the morning than at other times of the day. The risk appears to be highest just before waking, and during the first three hours afterwards. The incidence also spikes during the cold winter months.
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Early morning heart attack and stroke
A study in the British Medical Journal found the most common time to have a stroke was during sleep and during a morning peak between 08.00 hours and 10.00 hours. Another study from Greece found two peaks for stroke, one between 08.00 and 10.00 in the morning and another, lower peak between 16.00 and 18.00. This second peak was also associated with sleep, however, due to the traditional Greek habit of taking an afternoon siesta.
Analysis of circadian timing in over 11,800 strokes showed that, overall, the risk of stroke rises around 6am in the morning, with a 49% increase in strokes of all types between 6am and noon compared with other times of the day.
The onset of abnormal heart rhythms and heart attack is also more common in the early morning, rising to a peak frequency between 10.00 and 11.00 am. As a result, one in every 11 acute heart attacks and 1 in every 15 sudden cardiac deaths has been attributed to the early morning excess incidence.
Other studies have found that heart failure, pulmonary embolism (clot on the lung) and rupture or dissection of aortic aneurysms do not occur randomly through time, but also increased during winter, in December, on a Monday, and in the morning around 6am.
Why morning is such a dangerous time
Many biological processes have a natural variation throughout the day and night, known as your circadian rhythm. These include variations in blood pressure, heart rate, activity of the autonomic nervous system, secretion of hormones and blood clotting factors, blood vessel reactivity and even the oxygen requirements of your heart muscle cells.
Researchers believe there are two important circadian clocks involved in the onset of cardiovascular events: one in the brain, known as the central clock (found in the suprachiasmatic nucleus) and another molecular clock that is activated within individual cells, and is known as the peripheral clock.
These clocks are partly set by environmental cues, including exposure to light and the length of night and day. They regulate many body functions including hormone secretion, sleep, heart rhythm, blood pressure and heart rate.
The increase in heart attacks and stroke seen during the morning may partly relate to surging blood levels of the stress hormone, cortisol, and the resulting rise in blood pressure that occurs just before you wake.
Blood pressure surges in the early morning
The normal 24-hour variation in blood pressure is shown on the following graph. Blood pressure should remain below 140/80 mmHg (and ideally below 120/80 mmHg) during both the day and night, apart from a normal excursion upwards during exercise. Blood pressure should naturally fall during sleep, typically to below 100/60 mmHg, then rapidly rises just before you wake.
Typical 24 hour blood pressure variation in blood pressure
In someone with untreated high blood pressure, or poorly controlled hypertension, their blood pressure remains above 140/80 mmHg for most of the day and night, even during sleep, and surges to potentially dangerous levels just before and after waking.
Typical 24 hour blood pressure variation with untreated high blood pressure
This surge in someone with poorly controlled high blood pressure puts a significant stress on the heart and circulation, and causes microdamage (tears) to artery walls. This damage triggers blood vessel inflammation and the activation of blood cells involved in blood clotting and repair.
These natural defence systems also respond to your circadian clocks and influence the way your cells respond to circulatory damage at different times of the day. For example, over-activation of white blood cells and platelets could account for the increased risk of blood clots, heart attacks and strokes that occur in the early hours of the morning.
Blood clotting protection decreases in the morning
Researchers from Queen Mary University, London, recently found that people with cardiovascular disease have lower blood levels of a whole family of protective molecules in the morning. These protective substances (eg resolvins, protectins, lipoxins, maresins) are derived from omega-3 essential fatty acids, such as those obtained from oily fish. Low levels of these protective substances increase the risk of early morning blood clotting and increase the risk of cardiovascular events such as heart attack, stroke and pulmonary embolus.
The researchers collected blood at different times of day from 7 healthy volunteers and 16 people with cardiovascular disease.
In healthy people, blood levels of protective molecules increased during the early morning hours to prevent over-activation of white blood cells and platelets.
In those with cardiovascular disease, however, the production of protective molecules was significantly impaired. They found a marked morning increase in blood cell activation, and the clustering of white blood cells and platelets.
These changes are associated with increased blood stickiness, unwanted blood clots and blood vessel inflammation. Together with the circadian increase in heart rate just before getting out of bed, they could account for the increased risk of heart attack and stroke in the morning.
The researchers hope their discovery of the importance of these protective compounds could lead to new ways to diagnose, treat and prevent cardiovascular disease.
Suggested actions to help reduce morning risks
- Increase your intake of oily fish, or consider taking fish oil supplements
- If you have cardiovascular disease, talk to your doctor about the risks and benefits of taking mini-aspirin to reduce unwanted blood clots
- As an alternative to aspirin, consider taking a tomato extract called Fruitflow, which has been found to prevent unwanted blood clots as well as lowering blood pressure
- Ensure you maintain good control of your blood pressure throughout the day and night – monitor it before going to bed, on waking and during the day to see how it changes.
- If your blood pressure is not well-controlled throughout your waking hours, talk to your doctor about making any necessary changes to your medication; you may need to take one antihypertensive drug in the morning and another in the evening, for example.
- Explore all the different natural remedies for high blood pressure of which at least 45 are covered on this website.