Further research into the biomarkers in prolonged grief disorder has been deemed necessary, however, since oxytocin is a hormone associated with social connection, bonding and attachment-style in general, the hormone may be a place to center future study. One study found that there were higher oxytocin levels in those with prolonged grief disorder in comparison to those with major depressive disorder. Prolonged grief disorder is characterized as a stress response disorder and as such, it is warranted to take a look into cortisol levels and immune activation. A few studies have been done on this that have discovered higher morning cortisol levels in those with prolonged grief disorder which indicates possible dysregulation of the hypothalamic-pituitary-adrenal axis. While there has not been a significant amount of research done on the topic, areas such as the biology of stress responses, attachment and reward are of interest for future research.