Traumatic experiences from early childhood go on to negatively affect adults well into middle age, reports a new study published in Proceedings of the National Academy of Sciences (PNAS). Much of the connection between childhood stress and adult health is indirect, linked to unhealthy behaviors like smoking and drinking and weighs on body mass index and even socioeconomic status. However, there may still be a direct biological relationship between childhood trauma and adult health, which the scientists are still pursuing.

"These results come from a wider program of research where we're examining what we call the social and psychosocial environment," Michelle Kelly-Irving, a scientist at the French Institute of Health and Medical Research who co-authored the study, told The Verge. "So, how the social and psychosocial environment get under our skin from the earliest moments of life and lead us along health trajectories, which can explain health inequalities all across the life course."

There is already a growing body of work concerning childhood stress and how trauma can affect people as they develop, and today's study helps reinforce that literature. In the mid-1990s, the CDC and Kaiser Permanente HMO conducted the seminal Adverse Childhood Experiences (ACE) Study, which gathered information from more than 17,000 adults about their past experiences with abuse, neglect, and family dysfunction. The study found that negative childhood experiences can lead to alcoholism and chronic illnesses like heart disease in adulthood. Multiple studies have added to the ACE Study's findings in the years since.

The relationship between early-life trauma and stress later in life is mostly, but only in part, expressed through unhealthy behaviors, BMI, and socioeconomic status, the researchers say. Whether or not there is a direct biological link is plausible but unclear right now, though some research suggests that stress may have lasting effects on the nervous, endocrine, and immune systems. More work needs to be done to determine if that link definitively exists.

"I think this study is an important step forward," said Jamie Hanson, a postdoctoral fellow at the Center for Developmental Science at the University of North Carolina, Chapel Hill. Hanson co-authored a study published in Biological Psychiatry last year on how early life stress impacts parts of the brain. "We know that stress is related to negative health outcomes. Now, we can say adversity at [age] five can affect decisions made at 25, and that might be contributing to stroke risk at 50."

The researchers now hope that today's results provide reason for more research to take place in new contexts, like in developing nations, to better understand trauma's effects. From a public health standpoint, the study's findings might also be used in concert with the research already being published to help enact policies that can help intervene in abusive environments.