It’s pretty well-established at this point that having friends is good for you — over the years, study after study has found that social support is a significant predictor of a long, healthy life. The word friend, though, can mean so many things in so many different contexts: your work spouse, the old college pal you call when you feel like reminiscing, that person on the edge of your social circle that you always chat with at parties. Maybe you use “friend” to refer to a broad swath of people you enjoy hanging out with; maybe you reserve it for the few people you’d feel comfortable spilling your guts to.

According to one of the newest studies of the bunch, that last type of friendship may be one of the most valuable when it comes to your well-being: In a paper published last month in the journal Child Development, a team of researchers found that having a childhood best friend can play a significant role in a person’s mental health well into adulthood.

The study drew from a data set that tracked the mental health of 169 racially, ethnically, and socioeconomically diverse adolescent participants at three points: age 15, age 16, and age 25. For the first two rounds, subjects also identified the person they considered to be their best friend, and the study authors interviewed both members of the duo (the label of “best friend” didn’t have to be mutual, the authors noted, and participants didn’t necessarily have to name the same person both years).