A study of children evacuated from Finland during World War II and their siblings who remained behind found the descendants of women who were evacuated were much more likely to be hospitalized for mental illness. The research, published Wednesday in JAMA Psychiatry, adds to a small but growing body of research that suggests the impacts of trauma may be passed down across generations.Why it matters: "Our study's inter-generational findings demonstrate, yet again, that mental health is a 'life course' issue," study author Stephen Gilman tells Axios — and one that could affect multiple lives. This is particularly important because today's refugee crises don't just span years, they can last entire lifetimes, notes Gilman.

What they did: Past research has shown the 50,000 children who were evacuated from Finland during WWII were more likely to experience mental illness than those who were not. To control for pre-existing genetic tendencies towards mental illness, the researchers looked at the rates of hospitalization among the descendants of first cousins: 3,000 children who were descended from evacuees, and over 90,000 who were descended from siblings who stayed.

What they found: Daughters of women who were evacuated were four times more likely to be hospitalized for mental illness compared to their first cousins who stayed. This trend held true regardless of whether or not their mothers had been hospitalized for mental illness but was not true for male offspring or the descendents of men.

Take note: Because the study is retrospective, it's impossible to capture all the possible variables impacting the children. And since the study looks at hospitalizations for mental illness, it may be underestimating the scope of the problem, since mental illnesses are often underreported, particularly in men. Still, the large sample size and strong associations help account for some of these challenges.

The researchers weren't able to determine the cause for this trend, but they suggest two possibilities:

The experience of being evacuated may have impacted the parenting behaviors of the subjects in the study, or that stories of experienced trauma influenced the mental health of their children.

Or, intriguingly, this could be due to epigenetics — sometimes-inheritable changes in which genes are activated. Essentially, cells control which genes are "turned on" in a cell by attaching or detaching a molecule that can prevent the piece of DNA from being read. Past research has shown a physiological response to famine can be passed down across generations. One study found that the descendants of Holocaust survivors have different hormonal responses to stress, and another study from the same lab suggested epigenetics may explain why.

Go deeper: Rachel Yehuda, an author on both papers on multi-generational mental health impacts in Holocaust survivors, notes the gender trends could indicate something epigenetic is at work. Past research has shown mothers can pass on certain epigenetic changes while pregnant.

The bottom line: Epigenetics is a fledgling field, and the epigenetics of mental health is even younger. But, notes Yehuda, "Data like these really help make the argument that the effects of war are devastating well beyond the actual exposure and potentially for generations after," whether it be genetic or otherwise.