July 25 -- FRIDAY, July 24 (HealthDay News) -- Exposure to Agent Orange and other herbicides that were sprayed far and wide by the U.S. military during the Vietnam War might put veterans at increased risk for heart disease and Parkinson's.
An Institute of Medicine report released Friday finds "suggestive but limited" evidence of an elevated risk for these two conditions among soldiers who served in that conflict.
Agent Orange is made up of compounds known to be contaminated with a type of dioxin -- tetrachlorodibenzo-para-dioxin (TCDD) -- during manufacture. The chemical, named for the color of the barrel it was stored in, was one of the "broad-leaf defoliants" used in Vietnam to destroy vegetation to make enemy activity easier to spot.
Between 1962 and 1970, more than 20 million gallons of herbicides were sprayed in the jungles of Vietnam so that American forces could fight more effectively; Agent Orange was the herbicide used most often to accomplish this goal. The International Agency for Research on Cancer reclassified TCDD a group 1 carcinogen in 1997, a classification that also includes arsenic, asbestos and gamma radiation, according to background information in the study.
The IOM's report is the seventh update in a series requested by the U.S. Department of Veterans Affairs and mandated by Congress.
Parkinson's and heart disease were in the category of "inadequate or insufficient evidence until this report," said Richard A. Fenske, chair of the committee that compiled the report and a professor in the School of Public Health at the University of Washington in Seattle. "Those two have been moved to the limited or suggestive evidence of an association, and those are the only two that have been changed."
The "upgrade" of Parkinson's did not surprise Deborah Cory-Slechta, a professor of environmental medicine at the University of Rochester Medical Center in New York, but she said the outcome could have gone either way.
"It seems like it was on the fence a little bit," she said. "There are people who would argue the evidence is not very compelling at the current time."
Relationships between herbicides and Parkinson's disease have been noted in the epidemiologic literature, she said. "How close these are to herbicides of interest in this case is certainly more controversial," she added.
"Herbicides, yes. These specific cast of characters, I waffle about how strong that evidence is at this time," she said. "The committee recognized this, and I agree with their statement that this should be followed in some of the cohorts."
Recent studies have also suggested links between Agent Orange and aggressive forms of prostate cancer and high blood pressure.
Other committee findings, some confirming previously reported information, follow:
The committee noted there had been little or no follow-up on previous, similar recommendations.
More connections between exposure to these herbicides and different health problems are likely to come to light in the future, experts predicted.
"As we grow older, we become more fragile, and problems may not show up until we get more fragile," said Keith A. Young, vice chair for research at the Texas A&M Health Science Center College of Medicine, in the department of psychiatry and behavioral science. He is also neuroimaging and genetics core leader at the VA Center of Excellence for Research on Returning War Veterans at the Central Texas Veterans Health Care System.
"Differences tend to accumulate, and diagnoses get more sure and valid," he said. "As time goes on, the underlying pathology starts to break through, and we're able to see it more clearly. The chemical exposure did some damage that starts to be expressed as our bodies become more fragile."
The evidence "certainly point to the value of collecting lots of data on lots of different conditions to understand the effects of the environment on our bodies," Young said.
The Institute of Medicine has the full report.
SOURCES: Richard A. Fenske, Ph.D., associate chair, Environmental and Occupational Health Sciences, School of Public Health, University of Washington, Seattle; Deborah Cory-Slechta, Ph.D., professor, environmental medicine, University of Rochester Medical Center; Keith A. Young, Ph.D., vice chair, research, Texas A&M Health Science Center College of Medicine, department of psychiatry and behavioral science, neuroimaging and genetics core leader, VA Center of Excellence for Research on Returning War Veterans at the Central Texas Veterans Health Care System; July 24, 2009, Institute of Medicine report