date 1998 (IOM, 1999), Update 2000 (IOM, 2001), Update 2002 (IOM, 2003), and Update 2004 (IOM, 2005). In 1999, VA asked IOM to convene a committee to conduct an interim review of type 2 diabetes; that effort resulted in the report Veterans and Agent Orange: Herbicide/Dioxin Exposure and Type 2 Diabetes, hereafter referred to as Type 2 Diabetes (IOM, 2000). In 2001, VA asked IOM to convene a committee to conduct an interim review of childhood acute myelogenous leukemia (AML) associated with parental exposure; its review of the literature, including literature available since the review for Update 2000, was published in Veterans and Agent Orange: Herbicide/Dioxin Exposure and Acute Myelogenous Leukemia in the Children of Vietnam Veterans, hereafter referred to as Acute Myelogenous Leukemia (IOM, 2002). Also in 2001, Congress (PL 107-103) directed the Secretary of Veterans Affairs to ask NAS to review “available scientific literature on the effects of exposure to an herbicide agent containing dioxin on the development of respiratory cancers in humans” and to address “whether it is possible to identify a period of time after exposure to herbicides after which a presumption of service-connection” of the disease would not be warranted; the result of that effort was Veterans and Agent Orange: Length of Presumptive Period for Association Between Exposure and Respiratory Cancer, hereafter referred to as Respiratory Cancer (IOM, 2004).
In conducting their work, the committees responsible for those reports operated independently of VA and other government agencies. They were not asked to and did not make judgments regarding specific cases in which individual Vietnam veterans have claimed injury from herbicide exposure. The reports were intended to provide scientific information for the Secretary of Veterans Affairs to consider as VA exercises its responsibilities to Vietnam veterans.
In accordance with PL 102-4, the committee was asked to “determine (to the extent that available scientific data permit meaningful determinations)” the following regarding associations between specific health outcomes and exposure to TCDD and other chemical compounds in herbicides:
whether a statistical association with herbicide exposure exists, taking into account the strength of the scientific evidence and the appropriateness of the statistical and epidemiological methods used to detect the association;
the increased risk of the disease among those exposed to herbicides during service in the Republic of Vietnam during the Vietnam era; and
whether there exists a plausible biological mechanism or other evidence of a causal relationship between herbicide exposure and the disease.
The committee notes that both its congressional mandate and the statement of task are phrased with the target of evaluation being “association,” not “causal-