WASHINGTON—A new evaluation of existing scientific studies has found "limited or suggestive" evidence to link servicemen’s wartime exposures to herbicides in Vietnam with the development of acute myelogenous leukemia (AML) in their children. However, the Institute of Medicine (IOM) committee that reported the finding emphasized that the evidence for the association is not conclusive.
"No firm evidence links exposure to the herbicides with most childhood cancers, but new research does suggest that some kind of connection exists between AML in children and their fathers’ military service in Vietnam or Cambodia," said committee chair Irva Hertz-Picciotto, PhD, professor of epidemiology, University of North Carolina, Chapel Hill. "Additional studies are needed," she said.
The new report is one of a continuing series of evaluations of the effect of herbicides on human health. Many of the herbicides used in Vietnam, particularly the defoliant known as Agent Orange, contained dioxins.
AML accounts for 8% of all childhood cancers. Previous IOM reports cited "inadequate or insufficient" evidence to show an association between a father’s exposure and AML or other cancers in the children of Vietnam veterans.
According to the IOM, labeling the link "limited or suggestive" means the association is not conclusive enough to preclude that the finding was the result of chance or other factors, or that the studies reviewed failed to isolate all the variables that could have affected the outcome. "Inadequate or insufficient" means the available studies lacked scientific rigor, consistency, or statistical power to reach even tentative conclusions.
Some of the studies reviewed by the committee involved US Air Force and Army personnel who worked with the herbicides. Most of the studies, however, report the effects of herbicides on civilians who were exposed to the chemicals on their jobs or in industrial accidents.
Two major studies published in 2000 support the new AML finding. The two studies lack direct exposure measurements, but they provide persuasive evidence for several reasons, the IOM committee said.
Researchers conducting both studies used Vietnam veterans and specifically examined the risk of AML—not all childhood cancers—in their offspring. Moreover, in both studies, the strongest link was found in children diagnosed at the youngest ages, "a pattern that suggests that the cause of a disease stems from a parent," the IOM said.
A third study reviewed by the committee found that AML was more likely to develop in the children of men who were exposed to pesticides or herbicides in their work.
The report also reaffirmed earlier IOM findings. It found, for example, sufficient evidence to link herbicide exposure in Vietnam to the development in veterans of soft tissue sarcoma, non-Hodgkin’s lymphoma, Hodgkin’s disease, and chloracne.
Moreover, the committee said, studies continue to provide "limited and suggestive" evidence of a tie between herbicide exposure and several other diseases in veterans. These diseases include type 2 diabetes, respiratory cancers, prostate cancer, and multiple myeloma, as well as spina bifida in veterans’ children.
