After the dawn comes heart risk
The period after you wake up is the time of day when you run the greatest risk for cardiac events.
During the night, your cardiovascular system is "sleeping," characterized by low pressure and heart rate. But when your body wakes up, chemicals begin coursing through it with different effects on your circulation. For this reason you're at greater risk. Perhaps this is counterintuitive because you might think cardio distress would peak at times such as after a lot of daytime activity — say in the late afternoon.
But no. Because of the working of hormones and blood while you're asleep and the stress that can boil up from the subconscious during sleep, that's the time when you're at greatest risk for heart attack, aneurysms of the aorta and stroke. Harvard researchers estimated that the added risk of having a heart attack between 6 a.m. and noon was 40 percent — but they calculated that that relative risk tripled when taking into account just the first three hours after waking.
Waking and getting your motor running requires more myocardial (heart muscle) oxygen support, which triggers a peak in the production of the adrenal hormone cortisol, causing a hike in blood-pressure and blood-sugar levels. Hormonal spiking at this time of day also narrows vessel size, reducing blood flow to your coronary vessels. So you have competing issues: An increase in the body's oxygen need while holding out the prospect of decreased myocardial oxygen supply.
The early morning is also bad timing because of the stress that might be left over from REM (rapid eye movement) sleep, when it is thought most dreaming occurs. You have probably had the experience of waking up in a sweat from your last vivid dream of the night. That's stress on your system. You sometimes wake at dawn and aren't sure where you are— and you are trying to get reoriented, unfortunately, at the same time as your cardio system is going through what I described above.
Keep these circadian rhythms in mind if you're prescribed for hypertension drugs, and ask your doc whether it has 24-hour coverage.
