Potentially lethal heart rhythm disturbances – ventricular arrhythmias – are more likely to occur in the morning, when people awake after a night’s sleep, because of a surge in the stress hormone cortisol, research has concluded.
A study by Imperial College London found that ventricular arrhythmias are linked to a surge in cortisol, which peaks in the blood first thing in the morning.
The research, which was funded by the charity the British Heart Foundation, studied mice and found that cortisol binds to a specific protein on the surface of heart cells.
The protein then moves to a different part of the cell, where it influences genes that control how easily the heart cells carry the electrical signals that tell them to beat
As the activity of the genes change, electrical impulses to the heart become less regular and more chaotic, leading to the abnormal heart rhythms, or arrhythmia, the team found.
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Cortisol’s circadian rhythm is affected by sleep, with an increase in cortisol happening just minutes before an individual wakes up.
Lead researcher Alicia D’Souza, a BHF fellow at Imperial’s National Heart and Lung Institute, said: “Our hearts are effectively different organs at different times of the day. They are more vulnerable first thing in the morning because of ancient circadian rhythms, which have evolved over millions of years.
“All species have this in common, so although our study is in mice, we believe this is directly applicable to human and mammalian hearts,” she added.
The discovery of the link raises the prospect of new treatments in this field. Dr D’Souza and colleagues went on to show that, in mice, the injection of a drug that blocks the cortisol receptor can prevent the morning changes in so-called ion channels – and so also the morning vulnerability to heart rhythm disturbances.
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Professor James Leiper, BHF associate medical director, said: “Ventricular arrhythmias can strike at any time and, if left untreated, can lead to a loss of consciousness, sudden cardiac arrest, and death. It is crucial we continue to investigate the causes of these arrythmias, so we can take action to prevent them.
“This intriguing study in mice reveals a possible solution to the mystery of why ventricular arrhythmias are more common in the morning. Identifying a rise in cortisol as the culprit could allow us to explore new treatment options that could reduce arrhythmias in those most at risk. Further research will be necessary to establish whether these findings are also seen in humans,” he added.
