Heart attacks more common in the morning

Heart attacks are five to six times more likely to occur in the early morning hours between 1 and 5 a.m., and studies have shown that morning heart attacks tend to be more severe than those that happen later in the day.

Though it has often been assumed that this is partly due to the stress associated with going to work in the morning, a new study finds a more biological basis for the peak.

The study, published in the journal Nature, has identified a link between your circadian rhythm and the rise in early morning heart attacks.

Experts have known that the type of heart attack that tends to occur in the morning is called ventricular fibrillation, caused by a rapid irregular heart beat (rather than a heart attack caused by slowed heart rates).  The study, performed on mice, discovered events on the molecular level that can lead to these more rapid irregular heartbeats.

Levels of a protein called KLF15 vary throughout the day, following the lead of the circadian clock, which governs hormonal rhythms in your body.  The study found that having too low or too high levels of KLF15 set off a cascade of events that change the potassium current, affecting the electrical recovery time of heart muscle cells.

“This time interval is critical,” explains one of the study’s authors Dr. Xander Wehrens, professor of medicine in the department of cardiology at Baylor College of medicine in Houston, Texas.  “Too long or too short of an interval can result in abnormal heart rhythms called arrhythmias. As the heart loses the regularity of the beat, it cannot pump blood efficiently and a person can die suddenly."

The research needs to be repeated in humans to see if KLF15 is as important. If it is, it could lead to medications that target arrhythmias.

“Our work suggests that drugs that would fine tune electrical activity of the heart could perhaps prevent sudden cardiac death in the morning, but this remains to be studied,” says Wehrens.

For now, there is some evidence that the early morning increase in heart attacks is related to stress and a spike in stress hormones and blood pressure, so managing your stress would certainly be helpful, as would lowering all your risk factors for heart disease.

But this study suggests that the morning peak in heart attacks may be more biological than behavioral.