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News from the National Academies
Date: April 19, 2001
Contacts: Saira Moini, Media Relations Officer
Kathi McMullin, Media Relations Assistant
(202) 334-2138; e-mail <news@nas.edu>

FOR IMMEDIATE RELEASE

New Review Suggests Possible Association
Between Agent Orange and Form of Childhood Leukemia

WASHINGTON -- New evidence supports the possibility of an association between chemicals used in herbicides during the Vietnam War and the development of a form of leukemia in veterans' children, but it stops short of establishing a direct connection, says a new report from the Institute of Medicine (IOM) of the National Academies. The report is the latest in a series examining the impact of Agent Orange on human health.

Using the most recent scientific data, the committee that wrote the report evaluated whether veterans' exposure to the chemical defoliant Agent Orange and other herbicides used in Vietnam, some of which contained dioxin, is linked with the development of several types of cancer and other health problems in veterans and their children. The evaluation revealed new "limited or suggestive" evidence of an association with acute myelogenous leukemia (AML) in veterans' children, but the finding is not conclusive. Previous IOM reports found "inadequate or insufficient" evidence to determine whether a link existed for AML or other cancers in the children of veterans.

Leukemia is the most common type of childhood cancer. Acute myelogenous leukemia is a rapidly spreading form that originates in certain bone marrow cells. The disease accounts for about 8 percent of all childhood cancers. Little is known about what causes such diseases in children, how parental chemical exposures affect their offspring, or potential environmental risk factors for kids, the report notes.

"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, professor of epidemiology, University of North Carolina, Chapel Hill. "Additional studies are needed to shed more light on the issue."

Classifying evidence as "limited or suggestive" means that while there is evidence suggestive of an association between exposure and disease, it is not conclusive enough to say definitively that chance or other factors did not influence the results of the studies that were evaluated, or that the studies have isolated all of the variables that could have affected the outcome. A classification of "inadequate or insufficient" indicates that available studies lack the scientific rigor, consistency, or statistical power necessary to draw even tentative conclusions.

The ability of researchers to pinpoint the health risks faced by veterans is hampered by inadequate information about exposure levels of troops in Vietnam. Some of the evidence reviewed by the committee came from evaluations of U.S. Air Force and Army troops who worked with herbicides. Most information, however, was from studies of civilians who were exposed to herbicides on the job or in industrial accidents. Although most veterans probably experienced lower levels of exposure than people who worked with the chemicals over long periods in occupational or agricultural settings, it is difficult to say precisely which troops may have been exposed to higher levels.

A review of current literature, which included two major studies published last year, supported the new finding about AML, the committee said. Although the two key studies lacked direct measures of exposure, the research was persuasive for several reasons. For example, both studies were conducted with Vietnam veterans, and the associations were specifically with AML -- and not other forms of childhood leukemia. In addition, the strongest link was seen in children diagnosed at the youngest ages, a pattern that suggests that the cause of a disease stems from a parent. A third study found that the development of AML was more likely in the children of men who used pesticides or herbicides in their work.

The committee's congressionally mandated report also reaffirms earlier findings. There is sufficient evidence of a link between exposure and the development of soft-tissue sarcoma, non-Hodgkin's lymphoma, Hodgkin's disease, and chloracne in veterans. Additionally, scientific studies continue to offer "limited or suggestive" evidence of an association with other diseases in veterans -- including Type 2 diabetes, respiratory cancers, prostate cancer, and multiple myeloma -- as well as the congenital birth defect spina bifida in veterans' children.

U.S. forces sprayed Agent Orange and other defoliants over parts of south Vietnam and Cambodia beginning in 1962. Most large-scale sprayings were conducted from airplanes and helicopters, but considerable quantities of herbicides were dispersed from boats and ground vehicles or by soldiers wearing back-mounted equipment. A 1969 scientific report concluded that one of the primary chemicals used in Agent Orange could cause birth defects in laboratory animals. The U.S. military therefore suspended the use of Agent Orange in 1970 and halted all herbicide spraying in Vietnam the following year.

The committee's work was sponsored by the U.S. Department of Veterans Affairs. The Institute of Medicine is a private, nonprofit institution that provides health policy advice under a congressional charter granted to the National Academy of Sciences. A committee roster follows.
Read the full text of Veterans and Agent Orange: Update 2000 for free on the Web, as well as more than 1,800 other publications from the National Academies. Printed copies are available for purchase from the National Academy Press Web site or by calling (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).


INSTITUTE OF MEDICINE
Board on Health Promotion and Disease Prevention

Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides

Irva Hertz-Picciotto, Ph.D. (chair)
Professor
Department of Epidemiology
School of Public Health, and
Fellow
Carolina Population Center
University of North Carolina
Chapel Hill

Margit L. Bleecker, M.D., Ph.D.
Director
Center for Occupational and Environmental Neurology
The Children's Hospital Center for Reconstructive Surgery
Baltimore

Thomas A. Gasiewicz, Ph.D.
Deputy Director
Environmental Health Sciences Center, and
Professor of Environmental Medicine
Department of Environmental Medicine
School of Medicine
University of Rochester
Rochester, N.Y.

Tee L. Guidotti, M.D., M.P.H.
Professor and Chair
Department of Environmental and Occupational Health
School of Public Health and Health Services, and
Director
Division of Occupational Medicine
Department of Medicine
School of Medicine
George Washington University
Washington, D.C.

Robert F. Herrick, Ph.D., C.I.H., Sc.D.
Lecturer on Industrial Hygiene
Department of Environmental Health
Harvard School of Public Health
Boston

David G. Hoel, Ph.D.*
Distinguished University Professor
Department of Biometry and Epidemiology, and
Associate Director
Hollings Oncology Center
Medical University of South Carolina
Charleston

Loren D. Koller, D.V.M., Ph.D.*
Professor
College of Veterinary Medicine
Oregon State University
Corvallis

Howard Ozer, M.D., Ph.D.
Eason Chair; Chief of the Hematology/Oncology Section;
Director of the Cancer Center; and Professor of Medicine
University of Oklahoma
Oklahoma City

John J. Stegeman, Ph.D.
Senior Scientist and Chair
Department of Biology
Redfield Laboratory
Woods Hole Oceanographic Institution
Woods Hole, Mass.

David S. Strogatz, Ph.D., M.S.P.H.
Associate Professor and Chair
Department of Epidemiology
School of Public Health
State University of New York
Albany, and
Adjunct Professor
Department of Epidemiology
University of North Carolina
Chapel Hill

INSTITUTE STAFF

David A. Butler, Ph.D.
Study Director


* Member, Institute of Medicine