It's called the widowhood effect: the increased chance of death, particularly in older couples, when a person loses their spouse.

Now, scientists have discovered new evidence for why broken hearts and widowhood are in themselves a deadly danger to the recently bereaved – decoding hidden biological markers associated with severe cases of the grieving process.

A team led by psychoneuroimmunology researcher Chris Fagundes from Rice University examined 99 people who had recently become bereaved; they had lost their spouses, on average, less than three months prior.

A recent study by Fagundes had shown that widows and widowers are more likely to exhibit risk factors linked to cardiovascular illness and death, and here the team wanted to more deeply examine the culprit implicated: inflammation markers.

"Previous research has shown that inflammation contributes to almost every disease in older adulthood," Fagundes says.

"We also know that depression is linked to higher levels of inflammation, and those who lose a spouse are at considerably higher risk of major depression, heart attack, stroke and premature mortality."

In the new study, the researchers conducted interviews with each of the participants, classifying the level of grief they showed.

The team also took blood samples from the cohort, to examine whether elevated levels of depressive symptoms in bereavement correspond with higher levels of inflammation.

In their analysis, the researchers found bereaved individuals with a higher grief severity exhibited higher levels of various pro-inflammatory proteins called cytokines.

These signalling proteins – specifically the cytokines IFN-γ, IL–6, and TNF-α – saw the widows and widowers who displayed elevated grief symptoms experience up to 17 percent higher levels of inflammation.

Participants in the top one-third of that group exhibited a 53.4 percent higher level of inflammation than the bottom one-third of the group who did not exhibit severe grief symptoms.

While the previous findings already told us pro-inflammatory cytokines were higher in those who were recently bereaved, the new work gives us a clearer understanding of the associations and what they can mean.

"This is the first study to demonstrate that inflammatory markers can distinguish those who are widowed based on grief severity such that those who are higher on grief severity have higher levels of inflammation compared with those who are lower on grief severity," the authors write in their paper.

While it's early days, these links between grief severity, pro-inflammatory markers, and cardiac illness are starting to put together a picture that could help researchers design potential tools and treatments to identify and assist those at the greatest risk from the physical toll of bereavement.

"Now that we know these two key findings, we can design interventions to target this risk factor in those who are most at risk through behavioural or pharmacological approaches," Fagundes says.

It also goes to show that people experiencing the worst grief when they lose loved ones aren't just going through emotional hardship – their loss is so severe it's measurably impacting their own health and biological markers.

Helping people in those dark situations will never be as simple as just identifying their cytokine counts, but that knowledge could be what helps doctors prevent even further loss of life.

The findings are reported in Psychoneuroendocrinology.