The latest in a series of congressionally mandated biennial reviews of the evidence of health problems that may be linked to exposure to Agent Orange and other herbicides used during the Vietnam War found sufficient evidence of an association for hypertension and monoclonal gammopathy of undetermined significance (MGUS).
The committee concluded that there was sufficient evidence of an association between exposure to at least one of the chemicals of interest and MGUS, a newly considered condition. This finding is based on a recent study in which investigators found a statistically significant higher prevalence of MGUS in Vietnam veterans involved in herbicide spray operations than in comparison veterans. MGUS is a clinically silent condition that is a precursor to the cancer multiple myeloma, but only an estimated 1 percent of MGUS cases progress to multiple myeloma each year.
While some new studies suggest an association might exist between exposure to the chemicals of interest and Type 2 diabetes, the committee could not come to a consensus on whether this and the other available evidence continued to be limited or suggestive, or merited elevation to sufficient. Both newly and previously reviewed studies consistently show a relationship between well-characterized exposures to dioxin and dioxin-like chemicals and measures of diabetes health outcomes in diverse cohorts, including Vietnam veteran populations. The risk factors for diabetes, such as age, obesity, and family history of the disease, were controlled for in the analyses of most studies reviewed. However, some members of the committee believed that the lack of exposure specificity and the potential for residual uncontrolled confounding influences complicated attribution of the outcome to the chemicals of interest.
In addition, VA asked the committee to focus on three health outcomes: possible generational health effects that may be the result of herbicide exposure among male Vietnam veterans, myeloproliferative neoplasms, and glioblastoma multiforme. The evidence of association for exposure to the chemicals of interest and glioblastoma (and other brain cancers) remains inadequate or insufficient, the committee concluded. While it is appropriate for VA be mindful of the concerns raised about the possible association between Vietnam service and glioblastoma, the outcome is so rare and the information concerning herbicide exposures so imprecise, that it is doubtful that any logistically and economically feasible epidemiologic study of veterans would produce meaningful results regarding the association between exposures and the disease. For this reason, the committee recommended that VA should focus on fostering advancements to inform improved glioblastoma treatment options.
There are relatively few studies on the health effects of paternal chemical exposures on their descendants, and none address Vietnam veterans specifically. Therefore, the committee recommended further specific study of the health of descendants of male Vietnam veterans.
Myeloproliferative neoplasms and myelodysplastic syndromes are diseases of the blood cells and bone marrow. The committee’s search of epidemiologic literature yielded only one relevant paper on these diseases — a study of these cancers in Vietnam veterans that was reviewed in a previous update. Given this paucity of research, the committee recommended that investigators should examine existing databases on myeloid diseases to determine whether there are data available that would allow for an evaluation of myeloproliferative neoplasms in Vietnam veterans and others who have been exposed to dioxin and the other chemicals of interest.