Post-Traumatic Stress Disorder (PTSD) is a complex mental health condition that affects millions of people worldwide, often emerging after an individual has experienced or witnessed a traumatic event. According to the World Health Organization (WHO), approximately 3.9% of the global population has had PTSD at some point in their lives. This percentage is even higher in the United States, where about 6% of the population experiences PTSD. While PTSD is typically linked to trauma such as combat, assault, or car accidents, much remains unknown about how the body biologically responds to the stresses of trauma.
A significant breakthrough in PTSD research has come from a study conducted by anthropologists, social scientists, and veterans from Arizona State University (ASU) and the Naval Postgraduate School. This team of researchers conducted an in-depth analysis of how the hormones cortisol and testosterone affect PTSD in a non-industrialized society, specifically focusing on the Turkana people, a group of pastoralists living in Kenya near the South Sudan border.
The Uncharted Territory of PTSD Research
Most PTSD research thus far has been limited to individuals from Western or European industrialized societies. These studies typically involve people who have experienced trauma related to events such as car crashes, violent assaults, or multiple military deployments. For example, prior studies have shown that people diagnosed with PTSD tend to exhibit blunted cortisol levels throughout the day. Normally, cortisol levels fluctuate in a predictable rhythm—rising sharply in the morning and gradually decreasing over the course of the day, reaching their lowest point in the evening. However, individuals with PTSD often show little variation in these cortisol levels, leading scientists to believe that PTSD might disrupt the normal hormonal patterns.
But, what if these findings do not hold true for non-industrialized societies where the experience of trauma may differ in fundamental ways? This was the core question addressed by the research conducted by Ben Trumble, a research scientist at the Institute of Human Origins and associate professor at ASU. Trumble, alongside his colleagues, sought to examine how cortisol and testosterone levels manifest among the Turkana people, who, unlike participants in Western studies, lead a non-industrialized, pastoral lifestyle, facing unique and consistent traumas, particularly related to cattle raids and combat exposure.
Why the Turkana?
The Turkana people, residing primarily in the arid regions of northern Kenya, are pastoralists whose livelihoods are closely tied to livestock farming. This way of life involves significant risks, including exposure to violent conflict and trauma. The Turkana, especially the warrior class, frequently engage in cattle raids—often violent encounters with neighboring tribes over resources like water and pasture. These raids can involve intense firefights and result in the death of family members or the loss of livestock, both of which are critical to their survival. As a result, nearly 28% of Turkana men report symptoms of PTSD, making them an ideal group for studying the physiological effects of trauma exposure in a non-industrialized society.
One of the most significant advantages of studying the Turkana is their relatively homogenous exposure to trauma. Nearly every adult male Turkana warrior faces a similar degree of trauma, making it possible to compare individuals with PTSD to those without it, based on their shared experiences and cultural backgrounds. This is a stark contrast to previous studies where trauma exposure varies widely among participants, complicating the identification of consistent patterns of hormonal or physiological responses.
Hormones and PTSD: What the Study Found
In their study, the researchers primarily focused on two key hormones: cortisol and testosterone. These hormones play crucial roles in the body’s response to stress. Cortisol, often referred to as the stress hormone, is produced by the adrenal glands and is involved in regulating a range of bodily functions, including metabolism, immune responses, and the fight-or-flight reaction. Testosterone, on the other hand, is widely recognized for its role in muscle growth, reproductive function, and the regulation of mood, among other functions.
Previous studies in Western societies have shown that PTSD is associated with an abnormal cortisol pattern, where cortisol levels fail to exhibit the typical rise and fall throughout the day. The researchers at ASU and the Naval Postgraduate School wanted to test if the same hormonal disruptions would be found in the Turkana warriors who have PTSD.
The results were both surprising and significant. According to Michael Baumgarten, a graduate student at ASU and an Army Ranger veteran, the research team found that Turkana warriors with a provisional PTSD diagnosis exhibited no significant difference in cortisol patterns compared to those without PTSD. Both groups showed nearly identical cortisol fluctuations, challenging the idea that PTSD in this non-industrialized group leads to the same disruption in cortisol rhythms observed in Western populations.
Interestingly, however, the study revealed that Turkana men with PTSD had significantly lower testosterone levels upon waking compared to those without PTSD. This finding adds a new layer to the understanding of how trauma may affect the hormonal system, suggesting that while cortisol levels may remain relatively stable, trauma exposure in the form of PTSD could be linked to changes in testosterone levels.
Cultural and Environmental Factors
Why did the Turkana exhibit such different hormonal responses to PTSD compared to those in Western populations? According to the researchers, there may be several reasons for these discrepancies, including physical activity, cultural practices, and the unique nature of combat exposure.
The Turkana warriors are deeply embedded in a culture that actively promotes their status within the community. Unlike soldiers in industrialized nations who may struggle with reintegration and face societal stigma, the Turkana warriors are highly respected and supported by their community. After returning from a raid, warriors often participate in culturally significant rituals that involve both psychological and physical healing, providing a buffer against the negative physiological effects of trauma. Additionally, their physical activity levels—often involving long treks over challenging terrain—might contribute to a more balanced hormonal regulation that prevents the disruption of cortisol levels commonly seen in other PTSD-affected populations.
Furthermore, the Turkana’s warrior culture may act as a protective mechanism against PTSD’s harmful effects. As noted by Sarah Mathew, a research scientist at ASU, their strong community support and cultural acceptance of combat may provide resilience against the negative physiological outcomes of trauma exposure. Such cultural factors could mitigate some of the hormonal disruptions that typically accompany PTSD.
Future Implications and Areas for Further Research
The study conducted by ASU and the Naval Postgraduate School provides a crucial step forward in understanding the biological mechanisms of PTSD, but much remains to be explored. One major area of interest is why the Turkana show normal cortisol patterns despite high levels of trauma exposure. The researchers have speculated that the combination of physical activity, social support, and cultural practices might help protect them from the physiological damage seen in other populations.
The findings also highlight the need for more research on non-industrialized societies and their responses to trauma. As Matthew Zefferman, an assistant professor at the Naval Postgraduate School, notes, the study demonstrates that PTSD and its physiological impacts are not universal and may vary significantly across cultures. Cultural environment appears to play a crucial role in shaping how individuals respond to trauma and how the body regulates stress hormones.
In conclusion, the study of Turkana pastoralists offers invaluable insights into the complex relationship between hormones and PTSD. It challenges previous assumptions and suggests that biological and cultural factors may interact in profound ways, leading to vastly different physiological responses to trauma. Moving forward, research must continue to explore these differences in depth, ensuring that future PTSD treatments are sensitive to the diverse ways in which human societies experience and cope with trauma.
Reference: Matthew R Zefferman et al, Little evidence that posttraumatic stress is associated with diurnal hormone dysregulation in Turkana pastoralists, Evolution, Medicine, and Public Health (2025). DOI: 10.1093/emph/eoaf004