Most Service members are familiar with sleep as part of a healthy lifestyle. The recommended amount of sleep each night is between 7 and 9 hours and is considered adequate for most individuals (Watson et al. 2015). Achieving adequate nightly sleep has been shown to be important for mental health in the civilian population (Scott et al. 2021; Oftedal et al. 2019; Zhai et al. 2015).
Military-specific research has also investigated the contribution of sleep to Service member mental health. These studies, as well as a thorough review investigating 29 studies of both U.S. and non-U.S. military members (Farhadian et al. 2022), consistently identify adequate sleep as an important contributor to Service member mental health and well-being.
Nightly Sleep Duration and Service Member Mental Health
There is strong support for an association of inadequate sleep with depression, anxiety disorder, and post-traumatic stress disorder (PTSD; Hruby et al. 2021; Bigg et al. 2020; Osgood et al. 2019; Armenta et al. 2018; Taylor et al. 2014; Gehrman et al. 2013; Luxton et al. 2011). In most studies, sleeping less than 6 hours each night increased the likelihood that Service members would report having mental health disorder symptoms as compared with sleeping more than 6 hours each night (Hruby et al. 2021; Osgood et al. 2019; Taylor et al. 2014; Gehrman et al. 2013; Luxton et al. 2011). One study also suggested that for
each hour by which nightly sleep was reduced, the likelihood of reporting depression, anxiety, and PTSD symptoms was increased (Hruby et al. 2021). Moreover, even one night of shorter sleep was reported to worsen the severity of Service members' PTSD symptoms the next day (Bigg et al. 2020). Shorter sleep has also been suggested to play a role in cases where PTSD symptoms do not improve over time (Armenta et al. 2018). Unfortunately, there are few interventional studies designed to examine how changing Service members' sleep behaviors to help them achieve adequate nightly sleep might affect their mental health symptoms. Studies like this would clarify how improving nightly sleep duration might help Service members coping with mental health disorders.
In addition to the role that sleep may have in mental health disorders, studies have also suggested that inadequate sleep may negatively affect mental well-being by increasing emotional exhaustion (Mantua et al. 2021) and decreasing motivation (Ritland et al. 2019). However, additional research investigating associations between sleep duration and mental well-being are needed to confirm the benefit of adequate sleep on these outcomes specific to Service members.
Nightly Sleep Duration, Service Member Deployment, and Mental Health
Studies suggest that inadequate sleep may be one link between deployment and poor mental health. Service members who have deployed (Seelig et al. 2010) and/or experienced combat while deployed (Luxton et al. 2011) have been reported to sleep fewer hours each night. In one study of Soldiers surveyed approximately 90 to 180 days after returning from deployment, Soldiers who reported sleeping fewer than 6 hours per night were more likely to report symptoms of depression, PTSD, panic syndrome, and suicide attempts, even when combat exposure was considered as a contributing factor (Luxton et al. 2011). In another study of Service members both before and after deployment, inadequate sleep 30 days before deployment predicted a greater likelihood of PTSD after deployment (Gehrman et al. 2013). Short sleep has also been identified as a
moderator (a factor that influences the relationship between two other factors) of the relationship between combat exposure and mental health disorder. Researchers reported that sleeping fewer than 6 hours per night strengthened the relationship between combat exposure, mental health disorders, and poor or risky health behaviors in Soldiers who returned from a 9-month deployment (Osgood et al. 2019). Together, these studies suggest that deployment can influence Service members' sleep, and those who regularly sleep 6 hours or fewer each night may have worse mental health outcomes after deployment as compared with Service members who report sleeping more than 6 hours each night.
Potential Bi-directional Relationships between Sleep Duration and Mental Health
Research also suggests that mental health may influence the amount of nightly sleep reported by Service members (Biggs et al 2021; Seelig et al. 2010), and at least one study provides evidence of
bi-directional associations between sleep and mental health disorders (Hruby et al. 2021). In a bi-directional association, instead of one factor influencing another factor in one direction (factor “A" affects factor “B"), the two factors influence
each other (factor “A" affects factor “B" AND factor “B" affects factor “A"). In the 2021 study by Hruby and colleagues, inadequate sleep increased the likelihood that Service members would report mental health disorder symptoms,
and reporting mental health disorder symptoms increased the likelihood that Service members would report less time sleeping. This type of relationship could promote a cycle of inadequate sleep and poor mental health. Another study suggested a similar relationship between sleep and depressive symptoms (Bravo et al. 2018) but did not assess hours of nightly sleep, specifically. Additional longitudinal studies examining the relationship between sleep duration and mental health in the U.S. Military population would provide further support for these findings.
Limitations
Many of these studies were limited by use of potentially inaccurate self-reported data. For instance, study participants may have inaccurately estimated their nightly sleep duration. Future studies that measure sleep duration through use of wrist- or finger-worn activity or sleep trackers might further strengthen the evidence provided in these studies. Most mental health outcomes were also based on self-reported mental health symptoms, but it is unclear whether Service members who reported symptoms had ever been diagnosed with a mental health disorder by a healthcare professional. Moreover, self-reported health data may be subject to
social desirability bias. This type of bias occurs when study participants provide inaccurate information to cast themselves in a better light. For instance, some participants may have inaccurately reported sleeping more hours each night or experiencing fewer mental health symptoms to provide responses that made them appear healthier. This type of bias may be common in Service member populations since healthier lifestyle choices and better overall health are part of occupational requirements. Some studies were limited by cross-sectional design (data were only collected at one time-point). For this reason,
causality, the ability to know for certain that one factor caused another, cannot be determined; it is impossible to know if one factor occurred before another. However, the use of longitudinal and/or prospective study design (where data are collected from the same study participants more than once) by many of these studies strengthens this body of evidence. Finally, population characteristics (military branch, average age, pay grade, etc.) varied among studies, so some findings may not be broadly applicable to the U.S. Military. However, many studies were conducted with large populations of Service members across various branches of the U.S. Military, and relationships between sleep and mental health outcomes were consistent in most cases.
References and Brief Study Descriptions
This prospective cohort study was conducted to better understand the relationship between PTSD and various attributes of sleep, including sleep duration, from night to night and between weekdays and weekends. The study was conducted with a mixed population of 157 current and veteran Service members recruited from a large military treatment facility, of which 80 were identified as having possible PTSD and 77 did not meet the screening criteria for PTSD. In this study, participants answered questions about the duration and quality of their sleep each night for 15 days. Study participants with PTSD slept significantly less time each night as compared with participants who did not have PTSD. However, the variability of sleep duration, i.e., the measure of how participants’ time spent sleeping differed from night to night or between weekdays and weekends, was not different between Service members with PTSD and those without PTSD.
This cross-sectional, survey-based study was conducted to investigate whether there were relationships between self-reported hours of nightly sleep and self-reported symptoms of depression, anxiety disorder, or PTSD in U.S. Service members. In this study of more than 12,700 Army, Marine Corps, Navy, Air Force, and Coast Guard personnel, each hour by which nightly sleep was reduced significantly increased the likelihood of Service members reporting symptoms of depression, anxiety disorder, or PTSD. Moreover, when researchers compared the likelihood of any of the three mental health disorders between those who reported sleeping less than 7 hours each night and those who reported sleeping 7 hours or more each night, Service members who reported sleeping fewer than 7 hours each night were significantly more likely to report symptoms of depression, anxiety, or PTSD. When bi-directional relationships between sleep and any of the mental health disorders were investigated, the presence of self-reported depression, anxiety, and PTSD symptoms were all associated with Service members reporting significantly fewer hours of nightly sleep.
This longitudinal, prospective study was conducted to determine whether there was a relationship between sleep quality and/or quantity and indicators of occupational well-being, such as emotional exhaustion, role overload, or perceived stress. Specific to the topic of sleep duration, this study of 60 male Special Operations Soldiers found that shorter sleep duration 10 days prior to a 7-day training event was associated with greater emotional exhaustion after the 7-day training event. However, no other outcomes, including functional impairment, role overload, or perceived stress, were observed to be linked to sleep duration in this study. This finding suggests that shorter nightly sleep in the period leading up to physically and mentally demanding events may influence some, but not all, indicators of resilience and well-being.
This prospective study was performed to better understand how characteristics of nighttime sleep, including the amount of time spent sleeping, were related to PTSD symptoms the next day. The study included 61 current and former U.S. Service members diagnosed with probable PTSD. For 15 days, study participants answered questions about their nightly sleep, including sleep duration, and their daily PTSD symptoms. In this study, the amount of time an individual spent sleeping was predictive of the severity of their PTSD symptoms the next day such that less time spent sleeping was predictive of more severe PTSD symptoms the next day, even when multiple sleep characteristics, including trouble falling asleep and trouble staying asleep, were considered together.
This cross-sectional study was conducted to better understand how sleep quantity might predict associations between combat exposure and PTSD following return from a 9-month deployment to Afghanistan. Study participants were surveyed 3 months after their return from a 9-month deployment. Participants answered questions about their average nightly sleep duration during the most recent previous week and about combat exposures they experienced during deployment. In this study of 2,420 Soldiers, sleeping fewer than 6 hours per night was observed to influence the association of combat exposure and PTSD with adverse health behaviors such as alcohol consumption or risky behaviors. In other words, the associations between combat exposure, PTSD symptoms, and adverse health behaviors for Soldiers who reported sleeping fewer than 6 hours per night were significantly stronger as compared with Soldiers who reported sleeping more than 6 hours per night.
This prospective study was conducted to investigate whether the amount of nightly sleep had an impact on performance and motivation. Although this study was conducted with Reserve Officers’ Training Corps (ROTC) cadets, the findings may be reasonably applicable to Service members, keeping in mind the inherent differences and similarities between these two populations. In this study of 54 ROTC cadets, average nightly sleep time over 7 days was objectively measured using wrist-worn devices. When the association between nightly sleep time and motivation to perform was assessed, average total nightly sleep time predicted motivation to perform. Specifically, greater nightly sleep time predicted significantly higher levels of performance motivation.
This longitudinal study investigated factors, including sleep duration, related to persistent PTSD, which is PTSD reported by the study participants over the course of multiple years. The data collection time points consisted of a baseline data collection; a “first follow-up” data collection, which occurred 3 years after the baseline data collection; and a “second follow-up” data collection, which occurred 6 years after the baseline data collection. The number of participants at the first and second follow-up differed because only those participants who still reported PTSD symptoms (persistent PTSD) at the first follow-up were asked to participate in the second follow-up. Therefore, 2,409 active-duty Service members with probable PTSD provided information at the baseline and first follow-up. Subsequently, 822 Service members with probable PTSD at the baseline and first follow-up provided information at the second follow-up. Study participants answered questions about how long they slept each night and whether they had PTSD symptoms at baseline and again at each follow-up. Although sleep duration was not a significant predictor of persistent PTSD at the first follow-up, shorter nightly sleep predicted persistent PTSD at the second follow-up. In other words, shorter nightly sleep, in addition to other factors such as combat exposure, predicted the persistence of PTSD over the longer, 6-year term.
This cross-sectional study was conducted to investigate factors, including mental health, influenced by sleep disruption and inadequate sleep in Navy personnel serving in a combat zone. This study included 3,175 deployed active-duty and reserve U.S. Navy personnel who completed questionnaires about their sleep and mental health symptoms during Operation Enduring Freedom. The researchers reported that Service members who reported sleeping fewer than 6 hours each night had substantially higher likelihood of PTSD, anxiety disorder, and depression as compared with those who reported sleeping 6 hours or more each night.
This longitudinal study was conducted to understand whether there is a relationship between Service members’ reported nightly sleep duration prior to deployment and the development of mental health symptoms after their return from deployment. The study included more than 15,200 Service members who completed surveys both before and after deployment. Study participants with no mental health symptoms but who reported sleeping fewer than 6 hours per night in their initial, pre-deployment survey were more likely to report PTSD or anxiety symptoms in their follow-up survey, after returning from deployment. However, there were some differences in these associations between Service members who deployed between 2001 and 2006 and those who deployed between 2004 and 2008. Specifically, while the likelihood of reporting new-onset PTSD symptoms was higher for Service members who reported sleeping fewer than 6 hours per night regardless of when they deployed, the relationship between inadequate sleep and anxiety was only present in Service members who deployed between 2004 and 2008. This result suggests that there may be important, unaccounted for (in this study) differences among Service members who deployed at different times.
In this cross-sectional study, researchers were trying to better understand how often Soldiers who had recently returned from deployment reported inadequate sleep and how this lack of sleep might impact their mental health and the practice of “risky health behaviors.” Of the 2,738 Soldiers who participated in the survey-based study, inadequate sleep was frequently reported, as 72% reported sleeping 6 or fewer hours each night. Moreover, Soldiers who reported combat exposure during deployment were less likely to report sleeping more than 6 hours each night. Even when researchers considered the contribution of combat exposure to the likelihood of reporting symptoms of any mental health disorder and high-risk health behaviors, sleeping 6 hours or less each night increased the likelihood of reporting symptoms of depression, PTSD, panic syndrome, alcohol or tobacco product abuse, or suicide attempt.
This longitudinal study was conducted to better understand how deployment and return from deployment influenced various aspects of sleep, including nightly sleep duration. The study included 41,225 active-duty and reserve Service members from all branches of the U.S. Military who had never been previously deployed at the time of baseline survey data collection, between 2001 and 2003. During the first, or baseline, data collection, participants provided information about their nightly sleep characteristics during the previous month, including sleep duration and trouble sleeping. Participants also answered questions about any mental health disorder symptoms they may have experienced. A follow-up survey, which was sent to participants 3 years after they completed the baseline survey, asked the same questions about sleep and mental health disorder symptoms. For the analyses, researchers grouped participants into three different groups according to whether they had never deployed; had deployed but had been returned from deployment at least 2 weeks; or were currently deployed at the time of the follow-up survey. The researchers reported that deployment was a significant factor contributing to Service members’ sleep quality and duration. Additionally, study participants who reported PTSD or anxiety disorder symptoms at the time of follow-up were more likely to report significantly shorter nightly sleep duration at follow-up. However, mental health disorder symptoms reported during the baseline survey were not predictive of Service members’ reporting shorter sleep duration at follow-up.
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