Surprising PTSD Findings: Why Western Assumptions May Be Wrong

ASU scientists are the first to study the relationship between hormones and 3.9% of the global population has experienced post-traumatic stress disorder (PTSD) at some point in their lives. In the United States, this prevalence is higher, reaching about 6%.

PTSD can develop after an individual experiences or witnesses a traumatic event, with symptoms lasting for months or even years. However, much remains unknown about the condition.

Researchers from Arizona State University and the Naval Postgraduate School, including anthropologists, social scientists, and veterans, are the first to study the connection between the hormones cortisol and testosterone and PTSD within a non-industrialized society.

This new study sheds more light on the PTSD puzzle.

Homing in on hormones

Previous studies about PTSD and hormones have focused only on people living in Western or European industrialized societies. They included people who suffered from different types of trauma like car crashes, assault and multiple deployments, according to Ben Trumble, a research scientist at the Institute of Human Origins and associate professor at the School of Human Evolution and Social Change.

The studies showed the majority of people diagnosed with PTSD had very little change in their cortisol levels throughout the day. Instead, the results showed “blunted” levels of cortisol and not the normal rise and fall patterns.

“In healthy men, hormones like testosterone and cortisol follow a pattern throughout the day,” Trumble said. “Hormone levels are the highest just after waking up, and then decline rapidly. Levels are low throughout the day, and rise again at night.”

The big question Trumble and colleagues wanted to answer was, would they see this same pattern in a non-industrialized population with people who suffered from the same type of trauma?

“Our study is the first to examine associations between hormones (cortisol and testosterone) among the Turkana,” Trumble said. “Turkana pastoralists experience a high degree of combat exposure, and 28% of men have symptoms of PTSD. Because nearly everyone gets exposed to combat, we can see if there are biological differences in hormones for those with PTSD and those without PTSD. So, in this case we can compare apples to apples and not apples to oranges.”

What the ASU scientists found was surprising.

“We did not find any difference in cortisol for Turkana warriors with a provisional PTSD diagnosis versus those without PTSD,” said Michael Baumgarten, an Institute of Human Origins-affiliated graduate student and Army Ranger veteran. “Both groups of warriors had nearly identical cortisol patterns. Interestingly, Turkana men with PTSD had lower testosterone when they woke up compared to those without PTSD.”

“A more applied takeaway is to look at the results of this study and either retain or increase the level of skepticism one has of narratives that claim to have a crystal-clear picture of how human physiology responds to the stresses of combat — especially if they are trying to sell you something,” he said.

Why the Turkana?

Being a livestock farmer, or pastoralist, in Kenya near South Sudan can be dangerous and deadly.

The Turkana are mobile pastoralists and engage in cattle raiding, said Matthew Zefferman, an assistant professor at the Naval Postgraduate School and U.S. Air Force veteran.

Zefferman spent half a year in the field with the Turkana during his postdoctoral fellowship at ASU.

“The Turkana in our study area, who raid other pastoralists, typically do so across the disputed border with South Sudan,” he said. “They travel by foot, often over 60 miles and engage in small and large raids. They are also raided by members of other pastoral groups. These raids can result in firefights and the death of family members, and the loss of animals. About half of adult male deaths in the study area is due to raiding.”

Turkana warriors experience similar trauma from combat exposure during cattle raids. They also share similar cultural backgrounds and are the same gender. This differs from previous studies conducted where trauma and cultural background are different.

“It is interesting to see how the physiological response to trauma exposure can differ based on cultural environment,” said Sarah Mathew, a research scientist at the Institute of Human Origins and associate professor at the School of Human Evolution and Social Change. “It suggests that we can’t answer basic questions about human biology by only studying industrialized populations.”

Mathew’s relationship with the Turkana since 2007 led to this project and many others, providing valuable information about non-industrialized cooperation, cultural norms, and warfare.

While the study answers questions about hormonal regulation, there is still the question of why are the Turkana cortisol levels “normal” in those diagnosed with PTSD compared with Western populations?

The study cites many possible reasons including physical activity and cultural differences. The scientists say more research is needed.

A previous publication by Zefferman and Mathew stated that, unlike soldiers of nation-state societies, “Turkana warriors are strongly endorsed by the whole community, have elevated status, perform culturally sanctioned rituals after raids, and are deeply integrated with their corresponding civilian community.

“These longstanding cultural traditions of warriorhood may buffer them from some of the negative physiological responses to combat trauma.”

Mathew and the others emphasize the importance of sharing their findings with the Turkana. The researchers have engaged with the community over several years, and discuss findings from this and other ongoing studies and what these findings mean for future research.

“We can only do this research because of the support and help of the people we do the research with — the Turkana,” Zefferman said. “We acknowledge that their willingness to work with us is what has allowed us to do this research with potential benefits to our society.

“We go there at the grace of the people we work with.”

Reference: “Little evidence that posttraumatic stress is associated with diurnal hormone dysregulation in Turkana pastoralists” by Matthew R Zefferman, Michael D Baumgarten, Benjamin C Trumble and Sarah Mathew, 17 February 2025, Evolution, Medicine, and Public Health.
DOI: 10.1093/emph/eoaf004