A recent study published in Comprehensive Psychoneuroendocrinology provides insight into the biological mechanisms that may underlie post-traumatic stress disorder (PTSD). Researchers found that individuals diagnosed with PTSD showed reduced levels of the hormone oxytocin and elevated levels of vasopressin, a hormone involved in stress response. These findings suggest that an imbalance between these two hormones, particularly the ratio of vasopressin to oxytocin, could be a strong indicator of PTSD.
PTSD is a condition that can develop after someone experiences a traumatic event. It is well-known that traumatic experiences can have long-lasting effects on mental and physical health. While many studies have explored the psychological aspects of PTSD, researchers are still trying to fully understand the biological processes that contribute to the disorder. By identifying these processes, it may be possible to develop better diagnostic tools and treatments for people affected by PTSD.
In this study, the researchers focused on two key hormones, oxytocin and vasopressin, because both are involved in regulating stress and social behaviors. Previous studies have provided inconsistent findings regarding these hormones in people with PTSD, leading the researchers to conduct a more focused investigation. By comparing individuals with PTSD to two non-traumatized groups, they aimed to clarify the relationship between these hormones and the disorder.
“Trauma is, of course, one of the major problems in modern society,” said study co-author C. Sue Carter, a Distinguished University Scientist and Rudy Professor Emerita of Biology at Indiana University. “This study was a collaboration with a military officer, Major Alex Horn, who was completing a PhD in Biology. Dr. Horn’s study is unique in allowing comparisons with other types of stress, such as those experienced during an ultramarathon or SWAT team training. This work points us toward a different perspective on stress and could suggest novel approaches to managing and preventing PTSD.”
The study was carried out with a specific group of military veterans who had been diagnosed with PTSD, as well as two non-traumatized comparison groups: Special Weapons and Tactics (SWAT) trainees and endurance athletes.
The PTSD group consisted of 29 veterans, while the comparison groups included 11 SWAT trainees and 21 runners. All participants provided blood samples that were used to measure levels of oxytocin, vasopressin, and cortisol (another stress-related hormone) under resting conditions. Additionally, participants completed self-report questionnaires to assess their trauma exposure and PTSD symptoms.
For the PTSD group, hormone levels were measured multiple times during a two-week cognitive behavioral therapy (CBT) program. This allowed researchers to observe any changes in hormone levels in response to treatment.
The key finding of the study was that participants with PTSD had significantly lower levels of oxytocin and significantly higher levels of vasopressin compared to both the SWAT trainees and the endurance athletes. These differences were substantial—over twice the levels for each hormone. While cortisol levels did not significantly differ between groups, the ratio of vasopressin to oxytocin was particularly effective at distinguishing PTSD patients from the non-traumatized individuals.
“The differences in levels of oxytocin and vasopressin in PTSD were essentially categorical, and not seen in people exposed to other kinds of intense stress, but who did not experience the symptoms of PTSD,” Carter told PsyPost.
Additionally, as the PTSD patients went through their two-week CBT program, their oxytocin levels increased, and their vasopressin-to-oxytocin ratio decreased. However, the researchers did not find a strong correlation between these hormonal changes and the improvement in PTSD symptoms during the treatment period. This suggests that while the hormonal changes may be related to PTSD, they do not necessarily reflect the immediate effects of therapy.
“This study provides evidence that the oxytocin and vasopressin system should be a target for new therapeutic interventions for trauma victims and for prevention measures for anyone identified as having a high risk for stress-induced illness of any kind,” Horn said. “These hormonal systems, specifically the vasopressin system, have been overlooked by researchers and clinicians alike for decades. Our hope is that this study will increase awareness of the relevance of these peptides with regards to stress, trauma, and related disorders such as PTSD.”
But as with all research, there are some limitations. One limitation is that the study was conducted with relatively small sample sizes, particularly in the non-traumatized groups. Additionally, the participants in all groups were predominantly male, which limits the generalizability of the findings to women and other populations. Future research should include more diverse groups, both in terms of gender and trauma history, to see if these hormonal patterns hold true across different demographics.
Another limitation is that the study was observational, meaning that it cannot determine whether the changes in oxytocin and vasopressin levels caused PTSD or were a consequence of the disorder. Longitudinal studies that track individuals before and after trauma exposure could help clarify this relationship.
Moving forward, researchers will need to expand on this work by studying a wider range of populations and considering additional factors that could influence oxytocin and vasopressin levels. A better understanding of how these hormones interact with other systems in the body, such as the immune and nervous systems, could help clarify their role in PTSD. Additionally, researchers could explore whether treatments that specifically target oxytocin or vasopressin can help alleviate PTSD symptoms.
“This research supports the general hypothesis that oxytocin and vasopressin work as a system, capable of managing stress responses, as well as emotional and physical health,” Carter said. “We hope that this study will stimulate more research on this topic.”
The study, “Severe PTSD is marked by reduced oxytocin and elevated vasopressin,” was authored by Alexander J. Horn, Steve Cole, Hans P. Nazarloo, Parmida Nazarloo, John M. Davis, David Carrier, Craig Bryan, and C. Sue Carter.
