On November 30, 1939, 450,000 Soviet troops stormed across the Finnish border, setting off nearly five years of brutal conflict. The cities of Finland were strafed by bombers; severe food rationing was put into effect; roughly 2.5 percent of the population was killed. To protect Finnish children from the war, about 70,000 of them were evacuated to temporary foster homes in Sweden and Denmark.

At first glance, it seems like evacuating children from a war zone is the responsible choice. Nevertheless, multiple studies have found that those Finnish children who were sent away have had to deal with the more severe long-term consequences. They might have avoided the acute stress of war, but they had to cope with the chronic stress of separation. A 2009 study found that Finnish adults who were separated from their parents between 1939 and 1944 showed an 86 percent increase in deaths due to cardiovascular illness compared to those who had stayed at home. Although more than sixty years had passed since the war, these temporary orphans were also significantly more likely to have high blood pressure and type 2 diabetes. Other studies have documented elevated levels of stress hormone and increased risk of severe depressive symptoms among the wartime evacuees.

What explains these tragic correlations? The Finnish studies build on decades of research showing that disruptions to our early attachment relationships—such as separating young children from their parents during wartime—can have a permanent impact on our health.

The latest evidence in support of early attachment and adult medical outcomes comes from a new paper in PNAS by the scientists Michael Murphy, Sheldon Cohen, Denise Janicki-Deverts and William Doyle. But these researchers didn’t look at wartime evacuations – they looked at divorce. While parental divorce during childhood has been statistically linked to an increased risk for various physical ailments, from asthma to cancer, these studies have tended to rely on self-reports. As a result, it’s been difficult to determine the underlying cause of the correlations.

To explore this practical mystery, Murphy et al. came up with a clever experimental design. They quarantined 201 healthy adults and gave them nasal drops containing rhinovirus 39, a virus that causes the common cold. They carefully monitored the health of the subjects over the next five days, tracking their symptoms, weighing their mucus, and collecting various markers of immune response and inflammation.

The first thing the scientists found is that not all divorces are created equal. This accords with a growing body of evidence showing that the quality of the parents’ relationship with each other after separation may be more important in predicting the adjustment of their children than the separation itself. This led the scientists to ask their subjects whose parents lived apart if their parents spoke to each other after the separation. As the scientists note, “having parents who are separated and not on speaking terms suggests high levels of acrimony in the childhood family environment.” Such conflict can be extremely stressful for children.

How did these bitter separations during childhood impact the response of the adult subjects to a cold virus? The results were clear. Those adults whose parents lived apart and never spoke during their childhood were more than three times as likely to develop a cold than adults from intact families or those whose parents separated but were still on speaking terms. What’s more, the differences persisted even after the scientists corrected for a raft of possible confounding variables, such as demographics, childhood SES, body mass index, etc.

PLANS = Parents that Lived Apart and Never Spoke

There are two possible explanations for this increased risk. The first is that a bitter divorce weakens the immune system, making those subjects more vulnerable to the rhinovirus, even decades later. The second possibility is that divorce heightens the inflammatory response post-infection, thus triggering the annoying symptoms (mucus, sore throat, mild fever, etc.) associated with the common cold.

The evidence strongly favors the second explanation. For one thing, there was no statistical relationship between divorce and viral infection: everyone was equally likely to show antibodies to the virus in their blood. However, there was a large difference in how the body responded to the infection, with those from non-speaking divorced households being much more likely to exhibit symptoms of illness. (This increased risk was mediated by measurements of inflammatory cytokines.) Although it’s still unclear why an ugly divorce might alter our response to viral infection, one intriguing hypothesis is that the chronic stress of having parents who never stop fighting can cause immune cells to become desensitized to the very hormones that help suppress the inflammation response. In other words, an ugly parental separation can mark our stress response for life, an invisible wound we never get over.

This research is an important reminder of attachment’s long reach: even the most basic aspects of our physical health, like resistance to the common cold, are shaped by emotional events that happened decades before. But it’s also a demonstration that not every rupture of attachment leaves lasting scars; different kinds of divorce can have a very different impact on children. According to this data, the key element might be finding some way to constructively communicate with our former spouse, at least in matters relating to childcare. While intervention studies are needed to directly test this possibility, it seems likely that a little civility can help buffer the fallout of living apart.

Murphy, Michael LM, et al. "Offspring of parents who were separated and not speaking to one another have reduced resistance to the common cold as adults." Proceedings of the National Academy of Sciences (2017)