"Hooking up" and depression

Do attachment-free sexual encounters increase or decrease depression? Let me quote from this abstract:

"Young adults who reported more depressive symptoms and feelings of loneliness at Time 1 and subsequently engaged in penetrative hook ups reported fewer depressive symptoms and lower feelings of loneliness at Time 2 as compared to young adults who did not hook up. However, young adults who reported fewer depressive symptoms and were less lonely at Time 1 and engaged in penetrative hook ups over the 4 month period reported more depressive symptoms and greater feelings of loneliness at Time 2 as compared to young adults who did not hook up."

Holy regression to the mean, batman!