The death of a life partner may trigger an irregular heartbeat, itself potentially life-threatening, said new research Wednesday into the risk of dying from a broken heart.

A trawl of data on nearly a million Danes showed an elevated risk, lasting about a year, of developing a heart flutter. Under-60's whose partners died unexpectedly were most in peril.

The risk was highest "8-14 days after the loss, after which it gradually declined," said a study published in the online journal Open Heart.

"One year after the loss, the risk was almost the same as in the non-bereaved population."

Much research has focused on explaining the observed phenomenon of people dying soon after their life partner.

Several studies have shown that grieving spouses have a higher risk of dying, particularly of heart disease and stroke, but the mechanism is unclear.

The latest study asked specifically whether bereaved partners were more likely than others to develop atrial fibrillation, the most common type of irregular heartbeat and a risk factor for stroke and heart failure.

Researchers in Denmark used population data collected between 1995 and 2014 to search for a pattern.

Of the group, 88,612 people had been newly diagnosed with atrial fibrillation (AF) and 886,120 were healthy.

"(T)he risk of developing an irregular heartbeat for the first time was 41 percent higher among those who had been bereaved than it was among those who had not experienced such a loss," said the study.

Younger people, those under 60, were more than twice as likely to develop problems, and those whose partners were relatively healthy in the month before death, thus not expected to die, were 57 percent more at risk.

The team cautioned that no conclusions can be drawn about cause and effect, as the study was merely an observational one, looking at correlations in data.

Several factors that could throw the findings out of whack, such as the bereaved group's diet, exercise regime, or predisposal to AF, were not known.

The loss of a partner is considered one of the most stressful life events.

It can lead to mental illness symptoms such as depression, and can cause people to lose sleep and appetite, drink too much and stop exercising — all known health risks.