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1 Introduction
Pages 14-29

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From page 14...
... . Successor committees formed to fulfill the requirement for updated reviews produced Veterans and Agent Orange: Update 1996 (IOM, 14
From page 15...
... . In PL 107-103, passed in 2001, Congress 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)
From page 16...
... (The current committee has not modified the criteria used by previous VAO committees to assign categories of association to particular health outcomes but will henceforth state the object of its evaluation to be "scientifically relevant association" in order to clarify that the strength of evidence evaluated, based on the quality of the scientific studies reviewed, was a fundamental component of the committee's deliberations to address the imprecisely defined legislative target of "statistical association.") Following delivery of the committee's charge by a VA representative at the first meeting, the open session continued with brief presentations by other members of the public.
From page 17...
... Spina bifida in offspring of exposed people Inadequate or Insufficient Evidence to Determine an Association The available epidemiologic studies are of insufficient quality, consistency, or statistical power to permit a conclusion regarding the presence or absence of an association. For example, studies fail to control for confounding, have inadequate exposure assessment, or fail to address latency.
From page 18...
... Cancers at other and unspecified sites Infertility Spontaneous abortion (other than after paternal exposure to TCDD, which appears not to be associated) Neonatal or infant death and stillbirth in offspring of exposed people Low birth weight in offspring of exposed people Birth defects (other than spina bifida)
From page 19...
... CONCLUSIONS OF PREVIOUS VETERANS AND AGENT ORANGE REPORTS Health Outcomes VAO, Update 1996, Update 1998, Update 2000, Update 2002, Update 2004, Type 2 Diabetes, Acute Myelogenous Leukemia, Respiratory Cancer, Update 2006, Update 2008, and Update 2010 contain detailed reviews of the scientific studies evaluated by the committees and their implications for cancer, reproductive and developmental effects, neurologic disorders, and other health effects. The original VAO committee addressed the statutory mandate to evaluate the association between herbicide exposure and individual health conditions by assigning each of the health outcomes under study to one of four categories on the basis of the epidemiologic evidence reviewed.
From page 20...
... In accord with the court ruling, the committee was not seeking proof of a causal relationship, but any information that supports a causal relationship, such as a plausible biologic mechanism as specified in Article C of the charge to the committee, would also lend credence to the reliability of an observed association. Understanding of causal relationships is the ultimate objective of science, whereas the committee's goal of assessing statistical association is an intermediate (less well-defined)
From page 21...
... In response to a request from VA, the committee for Update 2008 affirmed that hairy-cell leukemia belonged in the category of sufficient evidence of an association with the related conditions CLL and chronic B-cell lymphomas. Health Outcomes with Limited or Suggestive Evidence of an Association In this category, the evidence must suggest an association between exposure to herbicides and the outcome considered, but the evidence can be limited by the inability to rule out chance, bias, or confounding confidently.
From page 22...
... The committee for Update 2000 was reconvened to re-evaluate the previously reviewed and new literature regarding AML, and it produced Acute Myelogenous Leukemia, which reclassified AML in children from "limited or suggestive evidence of an association" to "inadequate or insufficient evidence to determine an association." After reviewing the data reviewed in previous VAO reports and recently published scientific literature, the committee responsible for Update 2006 determined that there was limited or suggestive evidence of an association between exposure to the herbicides used in Vietnam or the contaminant TCDD and hypertension. AL amyloidosis was also moved to the category of "limited or suggestive evidence of an association" primarily on the basis of its close biologic relationship with MM.
From page 23...
... Health Outcomes with Limited or Suggestive Evidence of No Association The original VAO committee defined this category for health outcomes for which several adequate studies covering the "full range of human exposure" were consistent in showing no association with exposure to herbicides at any concentration and had relatively narrow confidence intervals. A conclusion of "no association" is inevitably limited to the conditions, exposures, and observation periods covered by the available studies, and the possibility of a small increase in risk related to the magnitude of exposure studied can never be excluded.
From page 24...
... The committees that produced VAO and the updates found that the body of evidence was sufficient for reaching conclusions about statistical associations between herbicide exposures and health outcomes but that the lack of adequate data on Vietnam veterans themselves complicated consideration of the second part of the charge. The evidence of herbicide exposure among various groups studied suggests that although some had documented high exposures (such as participants in Operation Ranch Hand and Army Chemical Corps personnel)
From page 25...
... The committee responsible for Update 2006 chose to eliminate the repetitive restatements in favor of the following general conclusion: "At least for the present, it is not possible to derive quantitative estimates of the increase in risk of various adverse health effects that Vietnam veterans may have experienced in association with exposure to the herbicides sprayed in Vietnam." The committee responsible for later updates and the current committee have opted to retain the modification in the formatting of the health outcomes sections. After decades of research, the challenge of estimating the magnitude of potential risk posed by exposure to the COIs remains intractable.
From page 26...
... The committee therefore believes that it is very unlikely that additional information or more sophisticated methods are going to become available that would permit any sort of quantitative assessment of Vietnam veterans' increased risks of particular adverse health outcomes attributable to exposure to the chemicals associated with herbicide spraying in Vietnam. Existence of a Plausible Biologic Mechanism or Other Evidence of a Causal Relationship Toxicologic data form the basis of the committee's response to the third part of its charge -- to determine whether there is a plausible biologic mechanism or other evidence of a causal relationship between herbicide exposure and a health effect.
From page 27...
... In addition to showing where the new literature fits into this compendium of publications on Vietnam veterans, occupational cohorts, environmentally exposed groups, and case-control study populations, it includes description and critical appraisal of the design, exposure assessment, and analysis approaches used. The committee's evaluation of the epidemiologic literature and its conclusions regarding associations between particular health outcomes that might be manifested long after exposure to the COIs are presented in the several chapters that follow.
From page 28...
... 2005. Comparison of the use of physiologically based pharmacokinetic model and a classical pharmacokinetic model for dioxin exposure as sessments.
From page 29...
... 2004. Veterans and Agent Orange: Length of Presumptive Period for Association Between Exposure and Respiratory Cancer.


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