Using extensive nationwide data, Danish researchers have found that the severely stressful life event of losing a partner is followed by an increased risk of atrial fibrillation, lasting for 12 months.

Atrial fibrillation is an abnormal heart rhythm connected with increased risk of stroke and heart attack.

The study, led by Simon Graff at Aarhus University, found that the overall risk of developing atrial fibrillation within 30 days of a bereavement was 41 per cent higher than the control group.

This was consistent over gender, time of year, pre-existing cardiovascular disease and diabetes.

What was most surprising from the research was that this risk was increased in those under the age of 60. These people faced a greater than 50 per cent chance of developing atrial fibrillation.

Those whose partners were relatively healthy in the month before death were 57 per cent more likely to develop atrial fibrillation, the study found.

The Heart Foundation in Australia says that the symptoms of atrial fibrillation include a "fluttering" heartbeat, an irregular pulse, weakness, tiredness and dizziness.

There is already evidence that stressful life events are linked to higher chances of heart attack, but this is the first widespread study that links such events to arrhythmic heart beat.

In 2014 The Journal of the American Medical Association published a study that found a doubling in risk of heart attack in individuals who had lost a partner within the past 30 days (from eight in 10,000 to 16 in 10,000).

The Danish study published on Wednesday used Denmark's extensive medical records from 1995 to 2014 with access to details of 5.6 million inhabitants.

The researchers collected information on 88,612 people newly diagnosed with atrial fibrillation and 886,120 healthy people.

Professor Garry Jennings, chief executive of the Heart Foundation in Australia, said the findings did not surprise him but "the strength of population data provides powerful evidence" for what we suspected anecdotally.

He said that atrial fibrillation was a "sleeper in the community" and that it was "probably the cause of a third of all strokes in Australia".

The health researchers in Denmark stressed the observational nature of their study.

"The underlying causal mechanisms for the association between the loss of a partner and atrial fibrillation is unclear," they reported.

Dr Graff told the Herald: "We are very excited about the study but of course cautious about making a direct causal link between atrial fibrillation caused by bereavement.

"However, between 7 and 10 per cent of atrial fibrillation cases are due to unknown causes, studies show. This is called lone-atrial fibrillation: it is not age-related or caused by heart disease or from excessive alcohol consumption," he said.

"This small amount has not been fully accounted for, so we may have found some of the percentages through this novel study."

The study is published on Wednesday in Open Heart, of the British Medical Journal.