ciations between herbicide exposure and the health outcomes, but the lack of adequate exposure data on Vietnam veterans themselves makes it difficult to estimate the degree of increased risk of disease in Vietnam veterans, as a group or individually. Thus, quantification of the actual risks experienced by veterans exposed to the compounds of interest during the Vietnam War is not possible.
Because of those limitations, only general assertions can be made about risks to Vietnam veterans, depending upon which category of the association has been attributed to a given health outcome. When there is “limited or suggestive evidence of no association” between herbicide exposure and a health outcome, the evidence suggests that there is no increased risk of the outcome among Vietnam veterans that is attributable to exposure to the compounds of interest, but that conclusion is limited to the conditions, exposures, and lengths of observation covered by the studies reviewed by the committee. Even qualitative estimates are not possible when there is “inadequate or insufficient” evidence of an association. For outcomes categorized as having “sufficient” or “limited or suggestive” evidence of an association with herbicide exposure, the lack of exposure information for Vietnam veterans prevents calculation of precise risk estimates.
IOM has been asked to make recommendations concerning the need, if any, for additional scientific studies to resolve continuing scientific uncertainties about the health effects of the herbicides and their contaminants used in Vietnam.
Great strides have been made over the past several years in understanding the health effects of exposure to TCDD and to the herbicides used in Vietnam and in elucidating the mechanisms that underlie those effects, but there are still important gaps in our knowledge. On the basis of its review of the epidemiologic evidence and consideration of the quality of exposure information available in existing studies, especially of Vietnam veterans, the present committee concludes that continuation of epidemiologic studies of veterans could yield valuable information.
Another population that has been understudied is the Vietnamese, including those who served in the military during the war and civilians. Anecdotal evidence and studies published in non-English-language journals suggest an array of long-term health effects that could potentially be related to the chemicals used by US troops in Vietnam. Although the explicit purpose of the newly established exposure database was to determine exposures of US service personnel who spent time in Vietnam, the possibility of using it to identify study populations among Vietnamese residents should be considered.