In recent decades, mental health providers began screening for "adverse childhood experiences" -- generally defined as abuse, neglect, violence, family dissolution and poverty -- as risk factors for later disorders.
But what if other things are just as damaging?
Researchers who conducted a large study of adults in Denmark, published Wednesday in the journal JAMA Psychiatry, found something they had not expected: Adults who moved frequently in childhood have significantly more risk of suffering from depression than their counterparts who stayed put in a community.
In fact, the risk of moving frequently in childhood was significantly greater than the risk of living in a poor neighborhood, said Clive Sabel, a professor at the University of Plymouth and the paper's lead author.
"Even if you came from the most income-deprived communities, not moving -- being a 'stayer' -- was protective for your health," said Sabel, a geographer who studies the effect of environment on disease.
"I'll flip it around by saying, even if you come from a rich neighborhood, but you moved more than once, that your chances of depression were higher than if you hadn't moved and come from the poorest quantile neighborhoods," he added.
The study, a collaboration by Aarhus University, the University of Manchester and the University of Plymouth, included all Danes born between 1982 and 2003, more than 1 million people. Of those, 35,098, or around 2.3 per cent, received diagnoses of depression from a psychiatric hospital.
As expected, adults who grew up in the poorer neighborhoods were more likely to suffer from depression, with increased risk of 2 per cent for each drop in neighborhood income level.
More surprising was the increased risk for adults who moved more than once between ages 10 and 15: They were 61% more likely to suffer from depression in adulthood compared with counterparts who had not moved, even after controlling for a range of other individual-level factors, the researchers found.
The study did not try to find reasons for this association, but Sabel speculated that moving was disruptive to children's social networks, requiring them to replace their friend groups, athletic teams and religious communities, all forms of what he calls "social capital."
"It's at a vulnerable age -- at that really important age -- it's when children have to take a pause and recalibrate," he said. "We think our data points to something around disruption in childhood that we really haven't looked at enough and we don't understand."
Losing Connection
Another surprise was that the negative impact of a move was not mitigated by moving to a more affluent area; adults who had moved from the poorest quintile of neighborhoods to the richest quintile had a 13% higher risk than counterparts who did not move. Those who moved from the richest to the poorest, by comparison, had an 18% higher risk than counterparts who did not move.
Sabel said this underlined the importance of social capital that develops within a settled community. Young people in disadvantaged neighborhoods are still "embedded in that community," he said. Moving to a wealthier neighborhood, he said, "you have all the disadvantage" of a poorer upbringing, in addition to the stigma of not fitting in.
One clear policy application, Sabel said, is for the management of children in state care. The data suggests that, for this vulnerable group, frequent moves between foster homes or residential care should be avoided, he said. It was more difficult to advise parents, he said, but he advised that, when contemplating a move, parents should consider its impact on children.
"The literature does clearly point to having stability in childhood, especially early childhood, is really, really important," he said.
It is unclear whether the Danish findings are applicable to Americans, who have high geographical mobility and tend to make longer-distance moves. The US Census estimates that an average American can expect to move 11.7 times in their lifetime; lifetime mobility in most of Europe is a fraction of that.
Shigehiro Oishi, a professor of psychology at the University of Chicago and the author of a 2010 study on the long-term effects of frequent moves in childhood, said that the negative effect of moves within the United States might be greater than within Denmark, since the differences in curriculum and quality of instruction would most likely be greater.
He called the paper "a landmark study" and "very, very methodologically strong." He said the authors could have looked more closely at the causal mechanisms, or at moderating factors that might explain why some children, but not others, were negatively affected by frequent moves.
Oishi's own study, which followed 7,018 adults for 10 years, found that the impact of moving frequently in childhood was worse among introverts, who reported lower well-being and life satisfaction and had a greater risk of death during the course of the study.
Oishi said the parents of introverted children should be warned about the long-term risks of moving in childhood. While moving is generally counted among the 40 most stressful life experiences, he said, his research suggests it ranks higher for children, in the top 5 or 10.
He added that, because residential mobility is not a disease, the study of it received little in the way of research funding.
A 2018 research study was able to establish causality by following families in public housing who were divided into two groups, one that remained in public housing, and one that used rental subsidy vouchers to move into better-off neighborhoods.
The study, which followed 2,800 young people in five US cities, found that mobility led to greater delinquency among boys between ages 13 and 16, though not for younger boys or for girls, suggesting that middle adolescence is a particularly sensitive period.