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Women are twice as likely to develop posttraumatic stress than men. It is not exactly clear yet why, but the female sex hormone, estrogen, appears to play a role.
Chemical structure of estradiol, the major estrogen sex hormone in humans. Image from Wikipedia By NEUROtiker – Own work, Public Domain.
Most of us (80-90%) will be exposed at least once in our lifetime to a traumatic event, which might range from dealing with an actual death or threatened by it, to serious injury and/or sexual assault. About 7% develop PTSD, or posttraumatic stress disorder, and about 30% will suffer from some of the same symptoms.
PTSD symptoms include:
- re-experiencing the trauma through flashbacks and nightmares
- Becoming emotionally numb and avoiding reminders of the trauma (e.g. people, places, etc.)
- Troubles relaxing and arousal: difficulty sleeping and concentrating; being overly alert; constantly watching out for signs of danger
Read more about PTSD here.
Trauma vulnerability
As many factors play a role in one’s vulnerability to traumatic events (more on genetic effects in an earlier blog), one factor seems to be gender. Women appear to be more vulnerable. This gender difference may be caused by social factors (e.g. what type of trauma you are likely to experience), or biological factors (e.g. differences in sex hormones). Studies have shown that the female sex hormone estrogen plays a role in one of the fundamental problems in PTSD, namely fear learning (how we learn/unlearn to fear something).
What is estrogen?
Estrogen is the primary female sex hormone and is responsible for the development and regulation of the female reproductive system. The most important naturally occurring form of estrogen is estradiol which regulates the estrous and menstrual female cycle. Next to these effects, it plays also a role in many other tissues, including bone, fat, skin, liver, and the brain. While estrogen levels are significantly lower in males compared to females, estrogen nevertheless has important effects in males.
Estradiol and fear learning
A study in rodents and later also in humans showed differential responses in women with high and low levels of estradiol. They found that high levels of estradiol in females, facilitate the learning process that a previously threatening event is no longer threatening anymore (we call this type of learning: fear extinction). Whereas, in contrast, females with low estradiol levels had problems unlearning that the previous event was no longer threatening and continued to fear the event. This was found in women with a normal hormone cycle (so not taking hormonal birth control).
To link these results to PTSD vulnerability, a study looked at estradiol levels in traumatized women, comparing women that suffered from PTSD and those without PTSD symptoms. Similar to the previous studies, they found that only traumatized women with PTSD and low estradiol levels, as opposed to traumatized women with PTSD and high estradiol levels, had problems with fear extinction. These women failed to suppress their fear to the event that was no longer threatening, unlike the traumatized women without PTSD symptoms.
In conclusion, we can say that estradiol plays a role in fear extinction learning in women. These results are of course difficult to generalize to men. Finally, it is an interesting question what this would mean for woman taking hormonal birth control, which generally suppresses natural estradiol levels. More research is needed to look further into this factor.
