WEDNESDAY, April 27 (HealthDay News) -- If you suffer a heart attack in the morning, it is likely to be more severe than having one at any other time of day, a Spanish research team reports.
In fact, if the heart attack happens between 6 a.m. and noon, it is likely to damage about 20 percent more heart muscle than a heart attack occurring in the afternoon or evening, the researchers added.
"It is well-known for several decades that the incidence of heart attack is variable across the time of the day, with higher incidence in the early morning hours," said lead researcher Dr. Borja Ibanez, from the National Center for Cardiovascular Research in Madrid.
It has been speculated, though not proven, that the body's circadian clock triggers the release of substances into the bloodstream that make the heart more prone to a heart attack at certain times of the day, he added.
"What was completely unexplored was the effect of the time of the day of onset of the heart attack on the extent of heart muscle death," Ibanez said. "This is the very first examination showing that the human heart has a variable tolerance to ischemia according to the time of the day."
The report was published in the April 27 online edition of Heart.
For the study, Ibanez's group collected data on 811 patients who had heart attacks between 2003 and 2009. Specifically, they looked at the amount of heart muscle damage in relation to the time the heart attack occurred.
The researchers found the most damage happened when the heart attack occurred between 6 a.m. and noon, compared with those whose attack occurred between 6 p.m. and midnight.
Ibanez's team determined the amount of damage done to the heart muscle by looking at the amount of two enzymes released during the attack -- creatine kinase and troponin-l. People whose heart attack occurred in the morning had 21 percent high
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