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Columbia University researchers, reporting in the Nov. 15 issue of the American Journal of Respiratory and Critical Care Medicine, found that those who suffered the most from PTSD were more than twice as likely to have asthma.
"This is very good data," said Keith A. Young, co-director of the Central Texas Veterans Health Care System Neuropsychiatry Research Program. "One of the things that is very clearly delineated by this study is that there truly is an association. This association has been seen with other anxiety disorders before, and there were some hints with PTSD, but this is the best. This kind of sets it in stone."
The challenge now is to find out whether this is a cause-and-effect relationship.
Previous studies have indicated a more general link between anxiety disorders and asthma, but this study focused specifically on PTSD, a disorder that involves nightmares, flashbacks and panic attacks linked to "triggers" that develop after exposure to combat or other extremely disturbing events.
This study looked at 3,065 male twin pairs listed in the Vietnam Era Twin Registry.
The twins were either identical (meaning they shared all the same genetic material) or fraternal (sharing only half their genetic material). Such twin studies are useful to science, because they can help tease out genetic and environmental influences.
The twins in this study had all lived together as children and had all served on active military duty in Vietnam. There were no significant differences in history of combat exposure or cigarette smoking. The overall prevalence of asthma was 6 percent and was about the same in identical and fraternal twins.
Twins who suffered from the most PTSD symptoms were 2.3 times more likely to have asthma when compared with those who suffered from the least PTSD symptoms. The increased risk was about the same for both fraternal and identical twins, suggesting an environmental underpinning rather than a genetic one.
"If there had been a strong genetic component to the link between asthma and PTSD, the results between these two types of twins would have been different, but we didn't find any substantial differences between the two," lead researcher Renee D. Goodwin, an assistant professor of epidemiology at the Mailman School of Public Health at Columbia University in New York City, said in a statement.
No one knows what the mechanisms are behind the association. It's possible that some sort of traumatic stress could trigger both PTSD and asthma, or one condition could contribute to the other.
"In my mind, the most likely thing that would relate these two is childhood stress," Young said. "It's very well-known that children who are a under a lot of stresses can grow up to have a different mental health outcome than their twin."
According to the study authors, understanding the association better may help PTSD prevention efforts by suggesting ways to modify environmental risk factors.
SOURCES: Keith A. Young, Ph.D., associate professor, psychiatry and behavioral science, Texas A&M Health Science Center College of Medicine, and co-director, Central Texas Veterans Health Care System Neuropsychiatry Research Program, Waco and Temple; Nov. 15, 2007, American Journal of Respiratory and Critical Care Medicine
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