Veterans and Agent Orange Update 2014 (2016) / Chapter Skim
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1 Introduction
1 Introduction
Pages 19-36
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From page 19... ...
The NAS was also asked to recommend, as appropriate, additional studies to resolve continuing scientific uncertainties related to health effects and herbicide exposures and to comment on particular programs mandated in the law. The original legislation called for biennial reviews of newly available information for a period of 10 1 Despite loose usage of "Agent Orange" by many people, in numerous publications, and even in the title of this series, this committee uses "herbicides" to refer to the full range of herbicide exposures experienced in Vietnam, while "Agent Orange" is reserved for a specific one of the mixtures sprayed in Vietnam.
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From page 20... ...
. In PL 107-103, passed in 2001, Congress directed the Secretary of Veterans Affairs to ask the 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)
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From page 21... ...
In accordance with its charge, the committee examined a variety of indicators appropriate for the task, including factors commonly used to evaluate statistical associations, such as the adequacy of control for bias and confounding and the likelihood that an observed association could be explained by chance, and it assessed evidence concerning biologic plausibility derived from laboratory findings in cell culture or animal model systems. As such, a full array of indicators was used to categorize the strength of the evidence.
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From page 22... ...
The comments and information provided by the public were used to identify information gaps in the literature regarding specific health outcomes of concern to Vietnam veterans. THE CURRENT POPULATION OF VIETNAM VETERANS In this last update in the series of reports mandated by PL 102-4 and PL 107-103, the committee wanted to make note of the number of Vietnam veterans who are still living and thus still possibly at higher risk than the general public for health consequences arising from their potential herbicide exposure in Vietnam.
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From page 23... ...
aBLS could not specify any change in methodology between 1995 and 1999 that would account for the increases in the estimated totals for both deployed and non-deployed Vietnam-era veterans in the civilian population, so the committee assumes that the increase is due to a large number of retirements from the military during that period. bBecause of decreasing totals, age brackets were not calculated separately for deployed and non deployed Vietnam veterans.
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From page 24... ...
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, Update 2010, and Update 2012 contain detailed reviews of the scientific studies evaluated by the committees and their implications for cancers, 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.
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From page 25... ...
The committee regarded evidence from several studies that satisfactorily addressed bias and confounding and that showed an association that is consistent in magnitude and direction to be sufficient evidence of an association. Experimental data supporting biologic plausibility strengthen evidence of an association, but are not a prerequisite and are not enough to establish an association without corresponding epidemiologic findings.
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From page 26... ...
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 *
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From page 27... ...
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)
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From page 28... ...
In addition, the possibility of a very small increase in risk at the exposure studied can never be excluded. There is limited or suggestive evidence of no association between exposure to the herbicide component of interest and the following health outcome: Spontaneous abortion after paternal exposure to TCDD aThis change in wording was made to emphasize the scientific nature of the VAO task and proce dures and reflects no change in the present committee's criteria from those used in previous updates.
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From page 29... ...
After the release of Update 2000, the researchers for one of the reviewed studies discovered an error in their published data. 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.
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From page 30... ...
Skin cancers were moved into this category in Update 1996 when inclusion of new evidence no longer supported its classification as a condition with limited or suggestive evidence of no association. Similarly, the Update 1998 committee moved urinary bladder cancer from the category of limited or suggestive evidence of no association to this category; in that case, although there was no evidence that exposure to herbicides or TCDD was related to urinary bladder cancer, newly available evidence weakened the evidence of no association.
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From page 31... ...
Health Outcomes with Limited or Suggestive Evidence of No Association The original VAO committee defined the category "health outcomes with limited or suggestive evidence of no association" 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.
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From page 32... ...
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 the consideration of the second part of the charge.
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From page 33... ...
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 it nontrivial to make this measurement but the hurdle of accounting for biologic clearance and extrapolating to the proper timeframe remains. Prior committees have thought it unlikely that additional information or more sophisticated methods would become available to permit any sort of quantitative assessment of Vietnam veterans' increased risks of particular adverse health outcomes that are attributable to exposure to the chemicals associated with herbicide spraying in Vietnam.
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From page 34... ...
In VAO and its updates before Update 2008, a considerable amount of detail was provided about individual newly published toxicology studies; the current committee concurs with the decision made by the committee for Update 2008 that it is more informative for the general reader to provide integrated toxicologic profiles for the COIs by interpreting the underlying experimental findings. In addition, when specific toxicologic findings pertinent to a particular health outcome are available, they are discussed in the chapter reviewing the epidemiologic literature on that condition.
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From page 35... ...
A new feature adopted in Update 2012 was the placement of a summary of the finding for each health outcome at the beginning of the chapter. Chapter 7, the first of the chapters evaluating epidemiologic evidence concerning particular health outcomes, addresses immunologic effects and discusses the reasons for what might be perceived as a discrepancy between a clear demonstration of immunotoxicity in animal studies and a paucity of epidemiologic studies with similar findings.
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From page 36... ...
In this last update mandated by PL 102-4 and PL 107-103, the committee also discusses how best to monitor the possibility of additional health outcomes associated with herbicide exposure. In the interest of minimizing unnecessary repetition, for the first time in this series of updates, the citations for all chapters have been merged into a single reference list that follows all the chapters.
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