© Springer Science+Business Media LLC 2018Eric Vermetten, Anne Germain and Thomas C. Neylan (eds.)Sleep and Combat-Related Post Traumatic Stress Disorderdoi.org/10.1007/978-1-4939-7148-0_4
4. Gender Differences in Sleep and War Zone-Related Post-traumatic Stress Disorder
Department of Psychiatry, San Francisco VA Medical Center and UCSF, San Francisco, CA, USA
The number of women currently entering the US Armed Forces and the scope of their involvement in combat operations are unprecedented. Women comprise 14.5% of active duty and 18% of National Guard and Reserve personnel . In addition to their increasing numbers, women are now eligible to serve in all positions within the military, including combat occupations, which put them at greater risk for exposure to combat and other military-related stressors. The mental health impact of serving in a war zone, particularly the development of post-traumatic stress disorder (PTSD), has been widely studied among male combat veterans. However, the increasing number and variety of roles among female military personnel serving in Operation Enduring Freedom (OEF, principally in Afghanistan), Operation Iraqi Freedom (OIF, principally in Iraq), and Operation New Dawn (OND, principally in Iraq)  allows a more comprehensive examination of gender differences in mental health outcomes related to serving in a war zone.
Numerous individual and environmental risk factors may influence whether exposure to trauma results in PTSD or other mental health problems. Although women in the general population have higher prevalence rates of PTSD than men , studies among military personnel and veterans report mixed results in the rates of PTSD and associated mental health outcomes [4–8]. Further examination of specific differences in symptom presentation among men and women exposed to traumatic events may reveal underlying mechanisms associated with the development of PTSD.
Studies among men and women exposed to civilian traumas (e.g., motor vehicle accidents, natural disasters, and terrorist attacks) indicate men and women respond differently immediately following a traumatic event [9–12]. Individual and trauma-related characteristics such as cognitive appraisal of traumatic events, neurobiology of stress response, and coping styles following traumatic events have been hypothesized to contribute to gender differences seen in PTSD . Gender differences in executive functioning and verbal memory following trauma have significant PTSD treatment implications.
In this chapter, we will review the types and extent of trauma exposure military personnel face in the war zone and associated mental health outcomes. We will also examine how men and women differ in the development of specific post-traumatic stress disorder symptoms, particularly sleep disruption, following a traumatic event. Biological, cognitive, and social mechanisms of these gender differences will be explored, and implications for PTSD treatment will be discussed.
Exposure to War Zone Stressors
Exposure to combat stressors places military personnel at risk of developing PTSD and other mental health problems following deployment to a war zone [14–16]. Although direct combat (e.g., being attacked or ambushed, being fired on or firing upon enemies) is most commonly associated with war zone stressors, there are several other stressors encountered during deployments including exposure to the aftermath of battle (e.g., handling remains), perceived threat (e.g., incoming mortar, IED explosions), and difficult living and working environment (e.g., heat exposure, sexual harassment or assault). Historically, men have reported significantly higher rates of exposure to combat stressors than women [3, 17]. However, trends in combat exposure among military personnel are changing as women assume a greater number and variety of roles in combat . Preliminary studies among OEF/OIF/OND cohorts demonstrate a closing gender gap in overall level of exposure, as well as significant gender differences among specific combat stressors experienced [5, 8, 19].
Level of Exposure
On average, women deployed to Iraq and Afghanistan experience less combat exposure than their male counterparts [3, 20, 21]. Nonetheless, women serving in OEF/OIF/OND conflicts experience substantial levels of combat exposure. A recent study among women deployed to Iraq found that 29% reported experiencing low combat exposure, 12% reported experiencing moderate combat exposure, and 3% reported experiencing high levels of combat . Another study found that approximately three-quarters of women deployed to Iraq experienced at least one or more combat experiences , which is comparable with studies conducted with primarily male samples . Consequently, women are facing more dangerous situations in combat, which is reflected in recent findings that to date, 1,027 women have been wounded in action and 166 killed while deployed in support of OEF/OIF/OND .
Type of Exposure
As the number of women serving in war zones has increased, researchers have examined gender differences among specific types of stressors experienced. Findings from a large sample of active duty men and women deployed to Iraq suggest that men are more likely to report being in fire fights (47% versus 36%, respectively) or report shooting or directing fire at the enemy (15% versus 7%). Conversely, 38% of women reported being involved in handling human remains compared to 29% of men, likely as a result of more female serving in medical roles . Similarly, a recent study found that men were more likely than women to endorse exposure to direct combat as part of a post-deployment screening . Although men reported higher rates of direct combat exposure, 31% of women reported exposure to death, 9% reported witnessing killing, 7% reported injury in the war zone, and 4% reported killing in war.
Military Sexual Trauma
In addition to combat stressors , female military personnel may be at increased risk for military sexual trauma (MST ) during deployment, including experiences of sexual harassment and sexual assault. While men are also exposed to MST, women generally confer a much higher risk of exposure to these types of interpersonal traumas during their military service [18, 24]. For example, Maguen and colleagues found that among active duty soldiers returning from deployment, 12% of women reported experiencing MST as compared to 1% of men . This is consistent with rates reported by Kimerling and colleagues, who found that among OEF/OIF/OND veterans seeking care at a VA medical facility, 15% of female veterans reported experiencing MST whereas less than 1% of male veterans seeking care reported MST .
Evidence suggests that exposure to sexual assault while in the military poses a greater risk for negative mental health outcomes as compared with nonsexual trauma in the military or sexual trauma as a civilian. Kang and colleagues found that among a sample of Gulf War veterans, experiences of combat exposure and sexual assault during deployment were both strong predictors of PTSD; however, sexual assault emerged as a stronger predictor . Another study found that sexual trauma experienced during military service was more strongly associated with adverse mental health outcomes like PTSD than was sexual trauma experienced before or after military service . MST has also been associated with greater risk for development of anxiety disorders, depression, and substance use disorders [25, 28, 29].
Additional Risk Factors for PTSD
There is a growing body of literature examining risk and resiliency factors associated with interpersonal relationships in the development of PTSD and other mental health problems among OEF/OIF/OND veterans [14, 18, 30]. Researchers have examined primarily three areas including (1) relationships prior to military service such as childhood family environment, (2) relationships between service members while deployed such as unit cohesion, and (3) relationships following military such as intimate relationships, parenting, and general social support. Additionally, multiple deployments to a war zone has become increasingly common among US military troops, which introduce a unique set of stressors that OEF/OIF/OND veterans have been facing such as personnel turnover within combat units between deployments and long periods of time away from family and friends over the span of several years. There are significant differences in how men and women in the US military are exposed to and manage these risk factors.
Research with military populations has demonstrated that the experience of multiple traumatic events across the life span can have a cumulative negative effect on veteran’s post-deployment adjustment and well-being . In their review of studies examining premilitary trauma, Zinzow and colleagues (2007) found that women were more likely than men to endorse trauma prior to military service, with 81–93% of female veterans reporting a history of at least one lifetime trauma. Nearly half of female veterans report a history of childhood physical or sexual abuse . It has been well established among general population samples that early childhood adverse events, often within the family environment, can lead to the development of poor coping skills and difficulties with emotion regulation . Given the high rate of interpersonal trauma experience by women entering the military, they may be at higher risk for revictimization or more likely to make internalized attributions as to why they have experienced military-related trauma which may place them at higher risk for developing PTSD .
Unit cohesion and positive appraisals of military service have been found to decrease the odds of developing PTSD post-deployment [4, 30], as has the perception of support from fellow service members and confidence in military leadership . In a sample of service members deployed to the Gulf War, women reported lower perceptions of social support from fellow service members [24, 33]. Among OEF/OIF/OND cohorts, sexual and gender-based harassment while deployed has been associated with higher risk for developing depressive symptoms . Perception of support from fellow military personnel may be particularly critical, when strong unit cohesion has been found to engender confidence and promote adaptive problem solving when under attack . Preliminary evidence in this area suggests that among women deployed to war zones, exposure to combat trauma may be exacerbated by the perceived lack of support from colleagues. A more comprehensive examination of working relationships among military personnel deployed to a war zone is warranted to further understand the potential protective effects of group cohesion, support, and strong leadership in the deterrence of negative mental health outcomes.
Post-deployment Interpersonal Functioning
Long months of separation from family and loved ones while deployed can create significant additional stress for men and women serving in war zones. Concerns about family and relationship problems are more strongly associated with post-deployment mental health for women service members than their male counterparts . Although similar proportions of women (38%) and men (44%) in the military are parents, women are three times more likely to be a single parent and five times more likely to be married to another service member who is also eligible for deployment . Previous research has shown that women who are single parents are more likely to report depressive symptoms and poor family functioning than women who are partnered in the period following deployment .
The presence of a supportive intimate partner may play a crucial role in coping with post-deployment stressors. Skopp and colleagues found that women who perceived greater decrements in intimate relationship strength were more likely to screen positive for PTSD, given higher levels of combat exposure . However, the same interaction was not found among women with lower combat exposure or men regardless of combat exposure level suggesting that the perceived loss of relationship intimacy may exacerbate PTSD associated with high combat exposure among women. Another recent study found that while the presence of post-deployment stressors increased the risk of post-traumatic stress disorder symptoms among both men and women, post-deployment social support mediated the relationship between post-deployment stressors and the development of PTSD among women . Taken together, it appears that interpersonal relationships following deployment may be particularly influential in the development of mental health symptoms among women.
Gender Differences in Mental Health Outcomes
The reported prevalence of mental health disorders, including PTSD, following deployment to a war zone varies widely across studies . Ramchand and colleagues found significant differences in overall prevalence rates based on sample selection (treatment seeking vs. nontreatment seeking) and how PTSD and other mental health disorders were operationally defined . Estimates of PTSD among active military personnel returning from combat deployment in Iraq and/or Afghanistan range from 4.6% to 24.5% using a four-item screen [5, 15, 23] and 6.2–31% using a 17-item self-report checklist assessing whether DSM-IV diagnostic criteria is met [4, 7, 16, 38–40]. Among OEF/OIF/OND veterans enrolled in the VA healthcare system, approximately 13–21.8% received a diagnosis of PTSD [41–43]. Despite the growing literature on the prevalence of PTSD among OEF/OIF/OND veterans post-deployment, few studies have examined gender differences.
Studies that have included women have found elevated rates of mental health disorders, including PTSD, yet results have been mixed. A nationally representative, longitudinal study of OEF/OIF/OND service members found that baseline rates of PTSD and other anxiety disorders were higher in females than males, whereas substance use disorders were more prevalent in males . Another large study of OEF/OIF/OND veterans found that females were more likely to screen positive for PTSD and depression than male veterans . A third study of OEF/OIF/OND veterans enrolled in VA care found that female veterans received depression diagnoses more frequently than male veterans, who were more frequently diagnosed with PTSD and substance use disorder diagnoses . These findings are supported by a fourth study among UK troops  that also found men were much more likely to endorse substance abuse and women were more likely to endorse depressive symptoms following deployment. However, some studies have found that female personnel were more likely than were their male counterparts to report depression, but no gender differences were found in the prevalence of PTSD [4, 5].
Other studies have specifically examined gender differences in combat exposure and mental health outcomes following deployment. Women who experienced low levels of combat were more likely to screen positively for PTSD and depression than their male counterparts with low exposure [20, 44]. This is consistent with studies of female veterans from previous eras who had significantly less combat exposure . Interestingly, there were no differences in mental health outcomes between men and women in the medium combat condition, and there were too few women in the high combat condition to make meaningful comparisons . Skopp et al. found that female soldiers with higher combat exposure more likely to screen positive for PTSD, as compared with their male counterparts . Luxton et al. replicated and extended these findings; female soldiers with higher combat exposure were more likely to screen positive for both PTSD and depression than their male counterparts . However, Woodhead and colleagues found that among soldiers exposed to high levels of combat, there were no gender differences among PTSD . Similarly, in a large cohort study (N = 4,684 matched subjects) of US military members who were followed between 2001 and 2008, researchers found that 6.7% of women and 6.1% of men developed PTSD and that there were no significant gender differences for the likelihood of developing PTSD or for PTSD severity scores among women and men who reported combat experience and among those who did not .
Multiple studies suggest minimal gender differences in the expression of PTSD following deployment to a war zone [4, 21, 44]. Maguen and colleagues found that while male OEF/OIF/OND military personnel did report greater exposure to combat experiences, there were no gender differences with respect to PTSD symptoms . Similarly, another study found that male and female veterans did not differ in the association between combat-related stressors and several mental health outcomes . However, Maguen et al. found significant gender differences in types of combat-related stressors experienced among OEF/OIF/OND military personnel; men reported higher levels of direct combat experiences whereas women reported higher levels of exposure to MST .
Although exposure to MST puts both men and women at increased risk for developing PTSD [25, 28], evidence suggests a stronger association between MST and PTSD in female veterans. Gender differences regarding the association between MST and depression and MST and alcohol/drug abuse have been mixed [25, 28, 48]. However, one recent study found that female veterans with PTSD and MST were more likely to receive a comorbid diagnosis of depression, anxiety, or eating disorders, whereas male veterans with PTSD and MST were more likely to receive comorbid substance use disorder diagnoses .
What still remains to be investigated, however, is whether specific post-traumatic stress disorder symptoms are manifested differently in men versus women following specific traumatic events. Additional information about how men and women initially respond to trauma, and how those responses may predict subsequent outcomes, may be particularly helpful in tailoring treatment interventions.
Gender Differences in PTSD Symptomatology
In addition to understanding whether women are more or less vulnerable than men in developing combat-related PTSD following deployment, it may be valuable to examine whether women manifest PTSD symptoms differently than their male counterparts. Peritraumatic responses have been found to be strong predictors in whether people will go on to develop PTSD . Examining gender differences in initial responses to traumatic events may inform why existing literature among civilians finds women are more likely than men to develop PTSD following a traumatic event [3, 50]. In a broad review of the literature, we found five studies among civilian samples examining differences in post-traumatic stress disorder symptoms following motor vehicle accidents (MVAs), natural disasters, and terrorist attacks. Consistent with existing literature, women in the following studies reported higher overall level of distress and number of symptoms, including greater problems with initiating and maintaining sleep. However, findings regarding gender differences among specific post-traumatic stress disorder symptoms are mixed.
Civilian Traumatic Experiences
One study examining the development of PTSD following a MVA found that women did not differ from men in meeting the overall reexperiencing criterion for a diagnosis of PTSD . However, women were 4.7 times more likely than men to meet overall avoidance criteria and 3.8 times more likely to meet overall arousal criterion. Specific symptoms such as intense feelings of distress in situations similar to the MVA and physical reactivity to memories of the MVA were significantly more common in women. Similarly, avoiding thoughts and situations associated with the accident, loss of interest in significant activities, and a sense of foreshortened future, as well as trouble sleeping, difficulty concentrating, and exaggerated startle response were also more common among women. Interestingly, gender differences remained even after controlling for overall symptom severity, prior trauma, peritraumatic dissociation, major depression or other anxiety disorders beside PTSD, and passenger injury.
In a second study, Bryant and colleagues found that women were more likely than men to meet criteria for acute stress disorder (ASD ) immediately following a MVA . Furthermore, meeting criteria for ASD was better predictor of developing PTSD 6 months following the accident among women as compared with men (93% versus 57%, respectively). Specifically, women were more likely to endorse peritraumatic dissociative symptoms (27% versus 10%) and avoidance symptoms (48% versus 37%), which is consistent with the previous study. However, unlike the previous study, Bryant and colleagues found that women were also more likely than men to meet reexperiencing symptoms (55% versus 34%) and men were somewhat more likely to endorse arousal symptoms than women (80% versus 76%) .
In a third study among survivors of MVAs, Irish and colleagues collected both self-report and objective data (e.g., heart rate and urinary cortisol levels) assessing levels of distress in the hospital immediately following the accident, and again at 6 weeks and 6 months . Women reported higher levels of overall distress , specifically in the perception of threat at the time of the accident, which is consistent with the previous two studies [9, 10]. Also consistent with previous findings, women were more likely than men to report peritraumatic dissociation immediately following the accident, which was predictive of developing post-traumatic stress disorder symptoms 6 month later. As a result of higher overall level of distress immediately following the accident and a higher level of peritraumatic dissociation, women were more likely than men to develop post-traumatic stress disorder symptoms at 6 months following the MVA. Interestingly, no gender differences were found among objective measures of distress (e.g., heart rate and urinary cortisol levels), which poses the question whether certain symptoms are more or less influenced by biology (i.e., physiological response to threat) or culture (i.e., expression of emotion, behavior).
Gender differences in the expression of PTSD symptoms have been hypothesized to be influenced by culturally defined roles and rules of masculinity and femininity . In a study among hurricane survivors, Norris and colleagues hypothesized that participants from cultures that adopted more traditional views of masculinity and femininity would endorse greater differences in their report of PTSD symptoms . Data was collected 6 months following Hurricane Andrew (Miami; White n = 135; Black n = 135) in 1992 and 6 months following Hurricane Pauline (Acapulco; N = 200) in 1997. Gender differences were most prominent in the Mexican sample; women reported higher scores on overall level of PTSD, intrusive, avoidant, arousal, and remorse symptoms. White women reported higher scores on overall level of PTSD and all other scales except remorse. Gender differences were attenuated among the Black sample; women reported higher scores on overall level of PTSD, intrusive, and arousal symptoms. Interestingly, sex differences in arousal symptoms were equal in all three culture groups, which support the earlier hypothesis that arousal symptoms following trauma are more likely to be influenced by biological vs. cultural factors.
A study of traumatic responses to the Loma Prieta earthquake (California, 1989) found similar results; women are more likely than men to report higher levels of intrusions and avoidance following a traumatic event . Women also reported a higher level of distress at the time of the earthquake. When asked an open-ended question about how long the earthquake lasts, women reported significant longer periods of time than men. Items related to hyperarousal were not included in the measure of post-traumatic stress disorder symptoms used in this study (Impact of Events) , so it is unclear whether gender differences would have been found. However, similar to the previous study examining responses to hurricanes , it appears that women are more likely to express distress following a natural disaster and have a more distressed experience of the event itself.
Two studies have examined differences in how men and women respond to terrorist attacks [53, 54]. Following the 2001 terrorist attack on the Pentagon, Grieger and colleagues gathered self-report data from 77 active duty military and civilian employees in order to explore differences in how men and women initially responded to the attack and subsequent coping behaviors . Women were found to have more peritraumatic dissociation and lower perceived levels of safety and were 5.6 times more likely to develop PTSD following the attack. Similarly, a study following terror attacks that occurred during the Al-Aqsa Intifada among Israeli citizens found that women reported a higher number of trauma-related symptoms and greater occupational impairment from those symptoms. Women also reported a greater number of dissociative symptoms than men, which has been a consistent finding across studies [9, 10, 12, 51, 54].
Across civilian studies, women consistently report a greater number of post-traumatic stress disorder symptoms and higher levels of distress following traumatic incidents. Although women are more likely to report dissociative symptoms following exposure to trauma, gender differences among avoidant, hyperarousal, and remorse symptoms remain mixed [10–12, 51]. It is also unclear whether findings from primarily civilian samples could be applied to a military population.