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. A conclusion of “no association” is inevitably limited to the conditions, exposures, and length of observation covered by the available studies. 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 herbicides of interest and the following health outcomes:

  • Spontaneous abortion after paternal exposure to TCDD, 2002

aHerbicides indicates the following chemicals of interest: 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and its contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), cacodylic acid, and picloram. The evidence regarding association was drawn from occupational, environmental, and veteran studies in which people were exposed to the herbicides used in Vietnam, to their components, or to their contaminant.

bEvidence of an association is strengthened by experimental data that support biologic plausibility, but its absence would not detract from the epidemiologic evidence.

SOURCE: Adapted from IOM (2009) and annotated to indicate the year of IOM finding and year of VA service connection.

linked to herbicide exposure in Vietnam and for which compensation is provided. Decisions regarding compensation are made by the VA, which takes both the VAO reports and other factors into consideration. For example, the VA recognizes non-Hodgkin’s lymphoma (NHL) as a service-related condition in Vietnam veterans, including Blue Water Navy veterans, but does not link it to Agent Orange exposure, although the VA website on these diseases does (http://www.publichealth.va.gov/exposures/diseases.asp).

In addition to reviewing previous VAO reports, the present committee heard from a number of veterans and is aware that many veterans attribute their illnesses to exposure to Agent Orange in Vietnam. The committee valued these accounts for descriptive purposes but did not have a way to use that information effectively in its study. Without an



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