The Adverse Childhood Experiences (ACE) Study is a massive, ongoing effort to understand the connections between what are generally labeled "adverse experiences" in childhood and their effects on adults decades later, even adults who don't remember or consciously acknowledge those experiences. You can go to their site and see how the ACE Score is calculated (pdf). And if you're brave enough, you can calculate your own score.
As the study's founder, Dr. Vincent Felitti, describes in a Big Think video, a score of six or more on this simple diagnostic is highly predictive of a wide range of adult diseases and behaviors, including dangerous obesity, IV drug use, attempted suicide, depression, and so on. The effect is not small - people with high scores on this assessment are 5000% more likely than the average for their age/gender/race/economic status to attempt suicide or have some form of eating disorder. Yes, that's five THOUSAND percent. The average life expectancy of the affected population goes down by 20 years.
Of course, discovering a massive effect is important but it's really only one step. Understanding the mechanisms is still a work in progress. Dr Felitti believes that in addition to the somewhat obvious (we engage in short-term pleasurable/long-term destructive behaviors in order to feel better) we also need to understand just how long-term, untreated stress affects every system in our bodies. In the past decade work has begun to emerge connecting untreated stress to subtle things like hormone production as well as its obvious effects on things like blood pressure.
Most sad for me is his final point, which is that he has come to believe that we cannot possible cope with the wide array of symptoms and diseases that crop up in people decades later - the only right solution is "primary prevention". In English, that means we have to treat our kids better, as a society. It's not enough to remove children from abusive situations and help them heal from it - we have to find ways to prevent that abuse. I'm sad because I don't even have the foggiest idea how to do that, or even what questions should be asked if we agree that's the goal we want to make progress against.
(For the record, my ACE score is exactly six.)