This study is one of a series of RAND reports that examine evidence relating to the possible link between exposure to a host of conditions and exposures experienced by U.S. military participants in that conflict and Gulf War illnesses.
This paper evaluates the available evidence concerning the link between stress and health problems in general, and the role of stress in the health problems experienced by Gulf War veterans in particular. The general scientific literature indicates that stress can have myriad health consequences, although no single health problem or set of symptoms is distinctively characteristic solely of stress, with the exception of posttraumatic stress disorder.
Health problems can stem from either disease or illness. While disease and illness overlap, they are distinct constructs. Disease refers to constellations of symptoms that define a diagnosable physical or psychiatric disorder; illness refers to the subjective experience of poor health. Illness manifests itself as somatic (bodily) or psychological symptoms, but may stem from multiple sources--including cognitive and social processes--and may or may not reflect the presence of an underlying disease. The relationship of illness to disease is complex. A person may experience ill health with no underlying disease. Conversely, the person may suffer from an underlying disease without perceiving himself or herself as ill.
In certain circumstances and for certain individuals, stressful experiences can contribute to health problems. For the purpose of this review, we define stress as a real or perceived imbalance between environmental demands required for survival and an individual's capacity to adapt to these requirements. Circumstances that individuals perceive as stressful trigger an integrated series of responses--physiological, behavioral, and psychological--to adapt to the environmental demands. Although these responses may have short-term benefits, over time they may act in concert with other host and environmental risk factors to increase the likelihood of psychological or somatic symptoms.
Physiological mechanisms implicated in illness and disease include the autonomic nervous system and neuroendocrine mediators that influence immune, gastrointestinal, neuromuscular, and cardiovascular reactions. Acute activation of these systems is known to precipitate short-term adaptive changes (e.g., rapid heart rate, increased perspiration, gastrointestinal motility) that may be experienced as symptomatic of ill health. Chronic activation of these systems is believed to enhance vulnerability to cardiovascular, metabolic, immune-related, and other diseases. Behavioral responses to stress can also heighten risk of illness. Individuals under stress are more likely to engage in behaviors with significant ramifications for health, including poor eating and sleeping habits and consumption of alcohol and other substances. Psychological mechanisms have been implicated as influencing health in at least two ways. First, patterns of thinking about oneself and one's world may place individuals at heightened risk for various forms of psychopathology, including depression and anxiety. Second, under stress, psychological factors may heighten an individual's perception of himself or herself as sick.
The general literature indicates that stress may be associated with a range of illnesses and diseases, but evidence of this linkage varies across problems. Little definitive evidence indicates that the stress of combat or war-zone exposure per se contributes to actual physical disease, although a number of epidemiological studies suggest that such exposure is associated with greater prevalence of self-reported chronic health conditions, poorer self-ratings of health, and higher levels of help-seeking behavior.
Members of the military are not alone in self-reporting health complaints in the absence of objectively verifiable disease; the empirical literature reports this as relatively common in the general population. Some evidence suggests that stress exposure and perceived stress may contribute to both medical help-seeking behavior and the experience of oneself as ill, even in the absence of objective evidence of disease.
Finally, evidence in the general literature suggests that virtually no stressful event or set of stressful circumstances produces health problems in every exposed individual. Certain persons may be more vulnerable to the potentially negative health consequences of stress exposure by dint of genetic or biological predisposition, prior life experiences, or personal and social coping resources as well as other factors.
Although these exposures were not reported to be stressful by all personnel, large numbers reported experiencing moderate to high levels of perceived stress resulting from various experiences. These findings were consistent across most studies and over time (e.g., two to three years following the Gulf War). The data were also consistent across male and female veterans, with few differences found in self-reported stress between the two groups.
In comparison to active-duty personnel, members of reserve component units--as a group--appear to have experienced somewhat higher levels of perceived stress, perhaps because of different expectations about military obligations, different levels of preparedness or training, or problems in the way they were utilized (e.g., units split apart and individual reservists assigned to other than their parent organization), among other factors.
What was stressful? As might be expected, actual combat topped the list. Other stressors included witnessing the death or disfigurement of American, coalition, or enemy forces, prolonged anticipation of the risk of serious injury or loss of life due to impending air and ground assaults, as well as to possible chemical-biological warfare and SCUD missile attacks. Iraq's past use of chemical and biological weapons heightened apprehension about possible attacks and raised concerns regarding the effectiveness of defensive suits. The possible side effects of required prophylactic drugs were also a concern. The media predicted that U.S. forces would suffer 20,000 to 50,000 casualties, further intensifying the pre-battle anticipatory stress. The threat of random SCUD missile attacks was theater-wide.
Low-level stressors came from many sources. Deployment itself was deemed stressful. The unexpected and rapid nature of the deployment created personal and family hardships, especially for members of reserve-component units. Once in theater, military personnel said they confronted a myriad of stress points: crowded or austere living conditions, long work days, a harsh climate, confinement to base camps with little opportunity for customary recreational outlets, separation from loved ones, and nearly total isolation from indigenous populations. Uncertainty about the length and nature of the mission compounded these hardships. Domestic worries, including concerns regarding separation from family and family-related problems, were another important source of stress reported by many Gulf War veterans.
A final source of stress reported by veterans stems from widespread and unrelenting concerns about the possible negative health effects of Gulf War service. Even before the war ended, efforts began to examine potential health problems associated with Gulf War service. Ambiguity concerning the origins of health problems reported by some Gulf War veterans continues to this day, with media accounts and conflicting reports contributing to an ongoing, stress-provoking climate of distrust, recrimination, and suspicion of government cover-ups and obstruction.
Gulf War and Posttraumatic Stress Disorder (PTSD). All fifteen studies that evaluated this relationship found evidence of a positive--albeit modest--relationship between stress exposure and PTSD symptoms. However, these studies were methodologically flawed. They relied on self-report measures or retrospective reporting of exposures, they contained little data from representative samples of deployed personnel, and they did not generally attempt to rule out other etiologic factors. As a result, these studies provide evidence--albeit suggestive--of a link between stress exposure and PTSD.
Gulf War and Non-PTSD Mental Health Problems. Ten studies reported on the relationship between stress exposure and other mental health problems. Although differing in numerous respects, including sample sizes and the operational definition of both stress exposure and mental health, most of these studies provided evidence of a relationship between stress exposure and psychological distress. These associations tended to be modest.
Like the PTSD studies, nearly all of these studies relied on veterans' self-reports of symptoms using symptom checklists, rather than diagnostic interviews. They also suffer from the same methodological problems. As a result, drawing definitive conclusions about the role of stress in non-PTSD mental health problems of Gulf War veterans is difficult.
Gulf War and Somatic Health Problems. Few studies were designed or reported in a manner that permits us to draw firm conclusions concerning the relationship between stress exposure and actual physical disease. We identified only four studies that directly report on the relationship between stress and bodily symptoms. These studies yielded mixed findings. In addition, they generally assessed physical symptoms using self-reports, which do not necessarily indicate an underlying organic cause and may merely reflect psychological distress. As a result, we found the Gulf War literature that evaluated a link between stress exposure and physical health to be quite limited.