Veterans and Agent Orange Update 2008 (2009) / Chapter Skim
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1 Introduction
1 Introduction
Pages 13-26
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From page 13... ...
The results of the original committee's work were published in 1994 as Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam, hereafter referred to as VAO (IOM, 1994)
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From page 14... ...
associated with parental exposure to any of the chemicals of interest; 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)
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From page 15... ...
When the first Veterans and Agent Orange committee received its charge from VA, service in the Republic of Vietnam was defined in Subsections a and f of Section 1116 of Title 38 of the United States Code as including military personnel who served in "the inland waterways of such Republic, the waters offshore of such Republic, and the airspace above such Republic." Using that definition, the original and later Veterans and Agent Orange committees routinely considered any research material pertaining to veterans from any of the armed forces who served in the Vietnam theater as relevant to its charge. It has recently come to the committee's attention that the definition of a qualifying exposure in VA's manual for processing veterans' applications was modified in 2002 and now limits presumption of exposure to Vietnam veterans
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From page 16... ...
There is limited or suggestive evidence of an association between exposure to the chemicals of interest and the following health outcomes: Laryngeal cancer Cancer of the lung, bronchus, or trachea Prostate cancer Multiple myeloma AL amyloidosis (category change from Update 2004) Early-onset transient peripheral neuropathy Porphyria cutanea tarda Hypertension (category change from Update 2004)
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From page 17... ...
By default, any health outcome on which no epidemiologic information has been found falls into this category. Limited or Suggestive Evidence of No Association Several adequate studies, which cover the full range of human exposure, are consistent in not showing a positive association between any magnitude of exposure to the herbicides of interest and the outcome.
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From page 18... ...
Chapter 2 provides details of the committee's approach to its charge and the methods it used in reaching conclusions. 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, and Update
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From page 19... ...
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. Science is principally concerned with causal relationships, and the committee's objective of statistical association is an intermediate (less well-defined)
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From page 20... ...
Experimental data supporting biologic plausibility strengthens evidence for an association, but is not a prerequisite. The original committee found sufficient evidence of an association between exposure to herbicides and three cancers -- soft-tissue sarcoma, non-Hodgkin's lymphoma, and Hodgkin's disease -- and two other health outcomes, chloracne and porphyria cutanea tarda (PCT)
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From page 21... ...
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 multiple myeloma.
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From page 22... ...
Health Outcomes with Limited or Suggestive Evidence of No Association The original Veterans and Agent Orange committee defined this category for health outcomes on which several adequate studies covering the "full range of human exposure" were consistent in showing no association with exposure to herbicides at any level 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 at the levels of exposure studied can never be excluded.
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From page 23... ...
Most of the evidence on which the findings regarding associations are based, therefore, comes from studies of people exposed to TCDD or herbicides in occupational and environmental settings rather than from studies of Vietnam veterans. 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.
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From page 24... ...
Even if one accepts an individual veteran's serum TCDD concentration as the optimal surrogate for overall exposure to Agent Orange and the other herbicide mixtures sprayed in Vietnam, not only is the measurement nontrivial but the hurdle of accounting for biologic clearance and extrapolating to the proper timeframe remains. The committee therefore believes that it cannot accurately estimate the risk to Vietnam veterans that is attributable to exposure to the compounds associated with herbicide spraying in Vietnam.
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From page 25... ...
Chapter 4 summarizes the toxicology data on the effects of 2,4-D, 2,4,5-T and its contaminant TCDD, cacodylic acid, and picloram; the data contribute to the biologic plausibility of health effects in human populations. Chapter 5 presents the relevant new epidemiologic literature identified in this update period, an overview of populations repeatedly studied by publications reviewed in the series of VAO reports with discussion of the exposure assessments conducted on the major cohorts, and design information on the epidemiologic studies that are newly covered in this update and investigated those populations or that report multiple health outcomes.
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From page 26... ...
2004. Veterans and Agent Orange: Length of Presumptive Period for Association Between Exposure and Respiratory Cancer.
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