The famous quote from the German philosopher Nietzsche, “That which does not kill us makes us stronger,” may not be true after all ― at least when it comes to mental health.
Results of a new study show that individuals who have a history of a stressful life events are more likely to develop posttraumatic stress disorder (PTSD) and/or major depressive disorder (MDD) following a major natural disaster than their counterparts who do not have such a history.
The investigation of more than a thousand Chilean residents ― all of whom experienced one of the most powerful earthquakes in the country’s history ― showed that the odds of developing postdisaster PTSD or MDD increased according to the number of predisaster stressors participants had experienced.
“We’ve learned that Nietzsche was wrong in this case and that the people who have had prior stressful and traumatic histories were more likely to develop PTSD and depression than those with fewer,” study investigator Stephen Buka, PhD, professor of epidemiology at Brown University, Providence, Rhode Island, told Medscape Medical News.
The study was published online June 11 in the British Journal of Psychiatry.
Stress Inoculation Hypothesis
The so-called stress inoculation hypothesis proposes that individuals who experience manageable stressors may be able to better cope with subsequent stressors, inasmuch as such experience affords them opportunities to practice effective coping skills and develop a sense of mastery over stressors.
It’s unclear whether the theory is true for individuals who are exposed to subsequent trauma, particularly with respect to such common mental health disorders as MDD and PTSD. Although less severe day-to-day stressors may be easier to cope with, major trauma can overwhelm an individual’s coping mechanisms.
Findings from previous research have been mixed. Some studies suggest that prior stressors can increase the risk of developing later psychiatric disorders. On the other hand, previous research has also shown that exposure to prior trauma alone does not predict subsequent PTSD.
Given these contradictions, the investigators wanted to determine whether a history of prior stressors was associated with psychiatric resilience among individuals who had no psychiatric history of MDD or PTSD.
“Only a small minority of people who have experienced a traumatic event go on to develop PTSD or MDD,” said lead author Cristina Fernandez, PhD, a psychiatric epidemiologist at the PAHO/WHO Collaborating Center for Research on Psychiatric Epidemiology and Mental Health, Warren Alpert Medical School of Brown University.
“So most people are resilient and move on without developing these disorders. But what is unique about this minority of individuals that makes them more susceptible to developing these disorders?” she continued. “It’s one of the most significant questions in the PTSD literature,” she added.
The analysis included data from 10 sites in the Chilean cities of Concepciόn and Talcahuano that had participated in the PREDICT investigation, a prospective cohort study that sought to predict mental health outcomes among primary care patients.
While the PREDICT study was being conducted, in February 2010, a major earthquake struck the coast of central Chile, killing more than 500 people and displacing 800,000. Concepciόn and Talcahuano experienced the most damage from the earthquake and its subsequent effects, including a tsunami that ravaged Talcahuano.
At baseline and 1 year after the disaster, all participants completed the Composite International Diagnostic Interview, which assesses for the presence of PTSD and/or MDD. Participants also completed the List of Threatening Experiences, a 12-item questionnaire that measures major stressful life events.
Of 3000 participants who initially agreed to take part in the trial, 1708 completed both the predisaster assessment in 2003 and the postdisaster assessment in 2011, 1 year after the earthquake and tsunami occurred. After excluding for a variety other criteria, 1160 individuals were included in the final analysis.
“As it turns out, it was a very natural experiment,” said Buka. “We had a group of people whose past traumatic experiences we knew about, and then they were all subjected to this terrible earthquake, and then we were able to look forward into time and see who did and didn’t develop PTSD and MDD.”
When the study began in 2003, none of the 1160 participants had a history of PTSD or MDD. After the 2010 earthquake, 9.1% of the survivors (n = 106) were diagnosed with PTSD, and 14.4% were diagnosed with MDD (n = 167).
Further analyses showed that prior disaster exposure was not a significant predictor of postdisaster PTSD. Nevertheless, for every unit increase in prior nondisaster stressors, the odds of developing postdisaster PTSD increased (odds ratio [OR], 1.21; 95% confidence interval [CI], 1.08 – 1.37; P = .001).
When categorizing predisaster stressors, the investigators found that individuals who had four or more predisaster stressors had a significantly greater chance of developing postdisaster PTSD than those with no predisaster stressors (OR, 2.77; 95% CI, 1.52 – 5.04).
Similar logistic regression analyses were performed for MDD, with comparable results. Although prior disaster exposure was not a significant predictor of postdisaster MDD, each one-unit increase in prior nondisaster stressors increased the odds of developing postdisaster MDD by 16% (OR, 1.16; 95% CI, 1.06 – 1.27; P = .001).
Categorization of these stressors revealed that experiencing any number of stressors significantly increased the odds of developing postdisaster MDD in a dose-response fashion.
In other words, every predisaster stressor ― even a single one ― increased an individual’s risk of developing postdisaster MDD, and each additional stressor further increased the risk.
Interestingly, the study also showed that the risk of developing both PTSD and MDD was particularly high among those who had experienced multiple predisaster stressors, such as serious illness or injury, death of a loved one, divorce, unemployment, financial struggles, legal troubles, or the loss of a valuable possession.
These findings, the researchers note, demonstrate that a history of stressors increases what they called “stress sensitization,” which may make individuals more vulnerable to the negative effects of subsequent stressors rather than more resilient.
As such, individuals who have experienced several stressors over the course of a lifetime are at higher risk of developing a psychiatric disorder.
This was the case with PTSD, in which exposure to at least four previous manageable stressors was associated with greater odds of developing postdisaster PTSD. For MDD, on the other hand, there was a distinct dose-response relationship between the number of manageable predisaster stressors and the risk for postdisaster MDD.
The investigators explain that these findings are particularly relevant in light of the COVID-19 pandemic and the current focus on racial and economic inequality in the United States. “The findings highlight the sectors of the population that are at greatest risk,” Buka said. “And those are the ones who’ve had more challenging and traumatic lives and more hardship.
“So it certainly calls for greater concentration of psychiatric services in traditionally underserved areas, because those are also areas that have greater histories of trauma.”
Commenting on the findings for Medscape Medical News, Patricia A. Resick, PhD, who was not involved in the study, said she found the research fascinating.
“The fact that they had preexisting data and then had the wherewithal to go back after the earthquake is quite amazing,” she said.
The findings came as little surprise to Resick, professor of psychiatry and behavioral sciences at Duke University Medical Center in Durham, North Carolina.
“I think most people are in agreement that the more stress you have, the more likely you are to get PTSD when you experience a traumatic stressor,” she said.
Treating these individuals remains a challenge, Resick noted, though knowing their history of stressors and traumas is an important starting point.
“We have to get a good history and figure out where to start treating them, because we always want to start with the event that causes the most PTSD symptoms,” she explained.
She also characterized the issue as being as much a public health concern as one for psychiatrists. “These are people you will want to have surveillance on and encourage them to get help,” Resick added.
“In the face of a disaster,” she said, “there needs to be more attention paid to vulnerable populations, because they likely don’t have the support they need.
“At the clinical level, these findings help the clinician know which patients are more likely to need more intensive services,” Buka added. “And the more trauma and hardship they’ve experienced, the more attention they need and the less likely they’re going to be able to cope and manage on their own.”
The study was funded by the US National Institute of Mental Health and FONDEF Chile. Fernandez, Buka, and Resick have disclosed no relevant financial relationships.
Br J Psychiatry. Published online June 11, 2020. Abstract