Contribution of emotionally traumatic events and inheritance to the report of current physical health problems in 4042 Vietnam era veteran twin pairs

Objective: To determine the contributions of psychological trauma (exposure to combat during the Vietnam War), genetic factors, childhood experiences shared by twin siblings, and unmeasured experiences not shared by twin siblings to the reporting of current physical health problems a mean of 19 years after military service. Methods: In 1987, a national sample of 2224 monozygotic and 1818 dizygotic male veteran members of the Vietnam Era Twin Registry participated in a survey of health. Genetic modeling was performed on cross-sectional physical health and combat exposure data derived from Registry twins. Results: Combat experiences explained a small proportion (0.7-8.4%) of the variance in the report of hypertension, respiratory conditions, persistent skin conditions, gastrointestinal disorders, joint disorders, and hearing problems. Childhood experiences shared by siblings are not clearly related to any health problem studied. By contrast, genetic factors explain 31 to 54% and noncombat experiences not shared by siblings explain 45 to 66% of the variance in current physical health status. Conclusions: Greater than 90% of the variance in reported current physical health problems in Vietnam era veterans is attributable to inherited factors and unmeasured environmental experiences not shared by twin siblings. The traumatic experience of combat makes only a small contribution to the report of current physical health problems. These results do not preclude the possibility that combat influenced the prevalence of illness shortly after military service or that combat may influence the development of illness in the future.