third part of the statutory charge—to determine whether there is a plausible biologic mechanism or other evidence of a causal relationship between herbicide exposure and a disease. This information is summarized in general terms in separate toxicology chapters in previous reports: Chapter 4 of VAO and Chapter 3 of Update 1996, Update 1998, and this report. Specific findings for each health outcome are also given in the chapters that review the epidemiologic literature.


The IOM was also asked to make recommendations concerning the need, if any, for additional scientific studies to resolve areas of continuing scientific uncertainty concerning the health effects of the herbicides used in Vietnam. Based on its review of the epidemiologic evidence and a consideration of the quality of exposure information available in existing studies, especially of Vietnam veterans, the committee responsible for VAO concluded that a series of epidemiologic studies of veterans could yield valuable information if a new, valid exposure reconstruction model could be developed. The original committee also saw value in continuing the existing Ranch Hand study and expanding it to include Army Chemical Corps veterans. The committee’s research recommendations emphasized studies of Vietnam veterans, rather than general toxicologic or epidemiologic studies of occupationally or environmentally exposed populations. A substantial amount of research on the toxicology and epidemiology of herbicides and herbicide components is under way in the United States and abroad. Indeed, many of the studies on which the committee’s conclusions are based have been published since 1991. Although this research is not targeted specifically to Vietnam veterans, it probably will also contribute to the knowledge of potential health effects in this population.

The committees responsible for VAO, Update 1996, Update 1998, Type 2 Diabetes, and this report have also made observations on research needs and opportunities regarding specific health outcomes and have offered advice on the conduct of future studies. The reports detail the committees’ comments on these topics.


IARC (International Agency for Research on Cancer). 1977. Some Fumigants, the Herbicides 2,4-D and 2,4,5-T, Chlorinated Dibenzodioxins and Miscellaneous Industrial Chemicals. IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man, Vol. 15. Lyon, France: World Health Organization, IARC.

IOM (Institute of Medicine). 1994. Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam. Washington, DC: National Academy Press.

IOM. 1996. Veterans and Agent Orange: Update 1996. Washington, DC: National Academy Press.

IOM. 1999. Veterans and Agent Orange: Update 1998. Washington, DC: National Academy Press.

IOM. 2000. Veterans and Agent Orange: Herbicide/Dioxin Exposure and Type 2 Diabetes. Washington, DC: National Academy Press.

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