Although most studies of social support deal with PTSD, particularly in Vietnam veterans, the same findings are applicable to major depression and other stress-related illnesses (Boscarino 1995; Fontana et al. 1997; Green et al. 1990b). Those studies all showed that low social support increased the risk of depression and other psychiatric disorders, such as generalized anxiety disorder.

Most findings regarding social support come from studies of homecoming support, whether given by family, friends, or community. A perceived lack of family cohesion has also been associated with PTSD in Gulf War veterans (Sutker et al. 1995b). Few studies have specifically investigated social support during the period of deployment to a war zone. In one such study of Vietnam-theater and Vietnam-era veterans (Stretch 1985), social support during and after deployment was found to be a major factor in development of PTSD symptoms (social support accounted for 12% of explained variance).

The lack of studies of the role of social support during deployment is an important gap because U.S. military personnel consistently report “being away from family” as a leading deployment stressor, according to several periodic DoD surveys of more than 12,000 active-duty military personnel serving in Iraq (MHAT 2006). The committee notes that it is difficult to determine whether low social support leads to mental-health sequelae, psychiatric problems reduce social support, or the relationship is indirect with other variables, such as the association of personality with both social support and other psychopathology.

Combat Exposure

One of the major risk factors for PTSD is exposure to combat. Combat as a deployment-related stressor was discussed in Chapter 3.

PTSD appears to be associated with intensity and length of combat exposure. Studies of veterans from the Vietnam War and the Gulf War have confirmed a dose-response relationship between level of combat exposure and likelihood of PTSD. A study of 641 Australian Vietnam veterans conducted 20-25 years after the war found a dose-response relationship between exposure to combat and PTSD (O’Toole et al. 1996). The prevalence of lifetime combat-related PTSD was 20.9% with the Australian version of the SCID and 11.7% with the DIS; the prevalence of current (1-month) PTSD was 11.6% with the SCID. When the prevalence of lifetime or current PTSD (based on the SCID) was compared with responses to a 21-item combat index, there was a linear dose-response relationship with increasing combat exposure. The OR for each combat-score quartile for lifetime PTSD was 1.00, 3.03, 5.36, and 9.18; for current PTSD, the OR was 1.00, 2.11, 6.97, and 10.33 for each quartile increase in combat exposure.

Dohrenwend et al. (2006) used NVVRS data on 1200 Vietnam-theater veterans to assess exposure to war-zone stressors. A diagnosis of PTSD was based on the SCID. A dose-response relationship between PTSD and exposure to war-zone stressors was established. Current (as of 1988) war-related PTSD was diagnosed in 0.3% of low-exposure veterans, 14.4% of moderate-exposure, 27.0% of high-exposure, and 28.1% of very-high-exposure.

Longer and more intense combat exposure is associated with a greater prevalence of current PTSD. One study of male twins discordant for serving in Vietnam found more PTSD symptoms in the Vietnam veterans than in their twins who did not serve in Vietnam, even 15 years after the war (Goldberg et al. 1990). Roy-Byrne et al. (2004) also compared PTSD in twins, of whom one had substantial combat exposure in Vietnam and the other had low or no combat exposure or did not serve in Vietnam. Over the 10-year followup, the number of PTSD

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