This research is based on ­something I was unaware of and that is people are more likely to have potentially fatal heart rhythm disturbances when they wake after a night’s sleep. Until now we haven’t known why this happens.

Turns out these abnormal heart rhythms are linked to the natural surge of cortisol, the stress hormone, which spikes in our blood first thing in the morning.

Thing is, cortisol binds to a specific receptor in heart cells which regulates heart beats. As a result, the heart becomes much more vulnerable, and it becomes easier for the regular ­electrical impulses that drive regular heart beats to break down into chaotic heart muscle activity, in other words, arrhythmia.

Cortisol is regulated by a 24-hour body clock and is affected by sleep. That’s why there’s a surge in cortisol just minutes before a person wakes.

The discovery of this link with cortisol also raises the prospect of new treatments for early morning ­arrhythmias. Dr Alicia D’Souza and colleagues from Imperial College London went on to show the injection of a drug that inhibits the cortisol receptor and prevents the morning vulnerability to heart rhythm ­disturbances.

This initial research was done in mice but nevertheless it’s important to human beings. Lead researcher Dr D’Souza from Imperial’s National Heart and Lung Institute (NHLI) points out: “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.”

By way of explanation, Professor James Leiper, Associate Medical Director at the British Heart ­Foundation, has 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 arrhythmias, so we can take action to prevent them.”

He goes on to emphasise the exciting implications of this research for the future development of ­treatments and preventatives.

“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.”