Studying more than 4,700 pairs of identical and fraternal twin brothers who served during the Vietnam War, the researchers found that combat played only a minor role in health problems, such as hypertension, respiratory difficulty and gastrointestinal disorders. The findings, reported in the Sept. 23, 1998 issue of the journal Psychosomatic Medicine, show that inherited factors and environmental experiences not related to combat explain more than 90 percent of reported health problems.

Past studies that have suggested an association between combat and physical health lacked adequate control groups, according to principal investigator Seth A. Eisen, M.D. He points out that while it is relatively easy to find subjects exposed to substantial psychological stress from combat, it is difficult to find an appropriate control group, individuals who are very similar yet lack combat exposure.

"Everything about the characteristics of people is explained by some combination of inherited factors and environmental experiences," explained Eisen, associate professor of medicine at Washington University School of Medicine and staff physician for the Department of Veterans' Affairs. "Twins provide a wonderful way to better understand this because if we find differences between twin siblings, those differences must be due to influences from outside of the family." Because the twins in this study were raised in the same households, they are as similar to each other as possible prior to entering military service. Identical twins have exactly the same genes, and fraternal twins share about half of their genes, so this sample also allowed the investigators to separate inherited factors from the influences of growing up in the same household environment.

Surveying identical and fraternal twins allowed the investigators to weigh the genetic and environmental factors that make up the mix of influences related to particular health problems. And because of the sample size, the odds are good that those influences will be true for all Vietnam veterans, not just the twins surveyed for this study.

Less than 9 percent of the Vietnam veterans suffered from hypertension, for example, but for identical twins, the odds were greater than 50 percent that if one twin had high blood pressure, so did his brother. Among fraternal twins, the overall rate of hypertension was 9.5 percent, and if one brother had it, his twin had a 34 chance percent of having it as well. Since the primary difference between pairs of identical and fraternal twins is the extent to which they share genes, this result suggests that inherited factors partially explain the development of hypertension.

Overall, the investigators found that, for the entire group of twins, inherited factors explained about 54 percent of the report of hypertension, while combat exposure explained less than one percent. For joint disorders such as arthritis, genetics accounted for 37 percent while combat exposure explained only 2.6 percent.

In all, combat experiences explained no more than 10 percent of the health problems reported by veterans. By contrast, Eisen and colleagues found that inherited factors and environmental experiences other than combat were much more important in determining whether health problems developed.

The researchers gathered data from the twins either by mail or telephone, using a 30-page questionnaire. When the original survey was conducted in 1987, the mean age of the twins/veterans interviewed was 38, and the average participant had been inducted into the service 19 years earlier.

"Frankly, one of the limitations of our study is that the individuals were surveyed while still relatively young," Eisen said. "It's quite possible that combat experiences and the persistent emotional problems that commonly result may eventually effect the veterans" physical health, but at this relatively young age, there's not yet any evidence that it had a significant effect."

The investigators, who also included researchers from the University of Illinois, St. Louis University, Boston University and Harvard Medical School, focused on several potential health problems. Those included hypertension, respiratory problems, skin conditions, gastrointestinal disorders, joint problems and hearing difficulty. Combat exerted the biggest influence on hearing.

"We know from previously published research that military personnel who have been exposed to loud artillery or combat noises end up having more hearing problems. Our study certainly supports this," Eisen said. "And the fact that our analyses found the expected results about the relationship between combat and hearing lends validity to our results with other health problems."

The only other health difficulty associated with combat involved the skin. Eisen is uncertain why combat veterans report a higher incidence of dermatologic problems, but he says it raises the issue that further study is needed.

The study also suggests to Eisen that if emotional distress from combat contributes to the development of physical illness in Vietnam veterans, it may be years before evidence of the link becomes clear. He suggests it would be worthwhile to survey the veterans again in a few years to evaluate both their psychological and their physical health status. He points to this summer's movie hit Saving Private Ryan as an example of the emotional impact of combat memories.

"Although the evidence is only anecdotal, when World War II veterans spoke to the press about their response to Private Ryan, it was clear how emotional these individuals became, even about events that occurred more than 50 years ago. I think that's just one recent example of a long-term psychological consequence of combat," Eisen says.

As the Vietnam veterans age, he says they may develop more problems with hypertension, heart disease or other difficulties that could result from many years of emotional distress that has its roots in their combat experiences.

"If individuals do have low levels of persistent psychological turmoil, they may have difficulties after a period of years because many of these diseases develop over decades," he explains. "That's why our observation that men in their later 30s don't have these health problems, while reassuring, does not preclude the possibility that they will develop problems later on."

Note: If no author is given, the source is cited instead.

• Chronic Illness
• Mental Health Research
• Teen Health

• PTSD
• Child Psychology
• Child Development

• Twin
• Heritability
• Multiple birth
• Gulf War syndrome
• Psychological trauma
• Post-traumatic stress disorder