Twin studies of veterans and adults suggest that approximately 30–46% of the variance in post-traumatic stress disorder (PTSD) is attributable to genetic factors. The remaining variance is attributable to the non-shared environment, which, by definition, includes combat exposure. This study used a gene by measured environment twin design to determine whether the effects of genetic and environmental factors that contribute to the etiology of PTSD are dependent on the level of combat exposure.

The sample was drawn from the Vietnam Era Twin Registry (VETR) and included 620 male–male twin pairs who served in the US Military in South East Asia during the Vietnam War era. Analyses were based on data from a clinical diagnostic interview of lifetime PTSD symptoms and a self-report measure of combat exposure.

Biometric modeling revealed that the effects of genetic and non-shared environment factors on PTSD varied as a function of level of combat exposure such that the association between these factors and PTSD was stronger at higher levels of combat exposure.

Combat exposure may act as a catalyst that augments the impact of hereditary and environmental contributions to PTSD. Individuals with the greatest exposure to combat trauma were at increased risk for PTSD as a function of both genetic and environmental factors. Additional work is needed to determine the biological and environmental mechanisms driving these associations.

Interest in the mental health of women deployed to modern military campaigns is increasing, although research examining gender differences is limited. Little is known about experiences women have had on these deployments, or whether men and women respond differently to combat exposure.

The current study used data from a representative sample of UK Armed Forces personnel to examine gender differences among those deployed to Iraq and Afghanistan (n=432 women, n=4554 men) in three measures of experience: ‘risk to self’, ‘trauma to others’ and ‘appraisal of deployment’. We examined the impact of such experiences on post-deployment symptoms of post-traumatic stress disorder (PTSD), symptoms of common mental disorder (CMD) and hazardous alcohol use.

After adjustment, men reported more exposure to ‘risk to self’ and ‘trauma to others’ events and more negative appraisals of their deployment. Among both genders, all measures of combat experience were associated with symptoms of PTSD and CMD (except ‘risk to self’ events on symptoms of CMD among women) but not with alcohol misuse. Women reported higher scores on the PTSD Checklist – Civilian Version (PCL-C) among those exposed to lower levels of each experience type but this did not hold in the higher levels. Women reported greater symptoms of CMD and men reported greater hazardous alcohol use across both levels of each experience type. Examining men and women separately suggested similar responses to exposure to adverse combat experiences.

The current findings suggest that, although gender differences in mental health exist, the impact of deployment on mental health is similar among men and women.