Veterans and Agent Orange Update 1996: Summary and Research Highlights (1997) / Chapter Skim
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EXECUTIVE SUMMARY
EXECUTIVE SUMMARY
Pages 1-14
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This IOM report presents the first updated review and evaluation of the newly published scientific evidence regarding associations between diseases and exposure to dioxin and other chemical compounds in herbicides used in Vietnam. For each disease, the IOM was asked to determine, to the extent that available data permitted meaningful determinations: 1)
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The committee was not asked to and did not make judgments regarding specific cases in which individual Vietnam veterans have claimed injury from herbicide exposure. Rather, the study provides scientific information for the Secretary of Veterans Affairs to consider as the DVA exercises its responsibilities to Vietnam veterans.
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Recent studies on the effects of TCDD and related substances on the immune system amplify earlier findings and suggest that these compounds affect primarily the T-cell arm of the immune response. Direct effects of TCDD on T cells in vitro, however, have not been demonstrated suggesting that the action of TCDD may be indirect.
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Since the publication of VAO, there has been considerable progress in the use of serum TCDD levels and/or quantitative exposure indices, as summarized in Chapter 5. There also has been progress in characterizing the TCDD body burdens in several groups, including the Ranch Hand cohort, Seveso residents, German herbicide production employees, and Vietnamese civilians (Michalek et
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From page 5... ...
Serum TCDD measurements may provide valuable information about past herbicide exposure under some conditions, and they are best used to detect differences in exposure levels among large groups in epidemiologic studies. This additional information on TCDD body burdens in specific groups and information on halflives allow more accurate comparisons of relative levels of exposure to TCDD among cohorts.
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For example, studies fail to control for confounding, have inadequate exposure assessment, or fail to address latency. There is inadequate or insufficient evidence to determine whether an association exists between exposure to herbicides and the following health outcomes: Hepatobiliary cancers Nasal/nasopharyngeal cancer Bone cancer Female reproductive cancers (cervical, uterine, ovarian)
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Neonatal/infant death and stillbirths Low birthweight Childhood cancer in offspring Abnormal sperm parameters and infertility Cognitive and neuropsychiatric disorders Motor/coordination dysfunction Chronic peripheral nervous system disorders Metabolic and digestive disorders (diabetes, changes in liver enzymes, lipid abnormalities, ulcers) Immune system disorders (immune suppression and autoimmunity)
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From page 8... ...
Because prostate cancer is one of the three cancer types of special interest to the DVA, a brief summary of the relevant scientific evidence is provided here. Because spine bifida, acute and subacute (transient)
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Thus, all three epidemiologic studies (Ranch Hand, VES, CDC Birth Defects Study) suggest an association between herbicide exposure and an increased risk of spine bifida in offspring.
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peripheral neuropathy. There are several published studies relevant to this health outcome, but they are primarily case histories from occupational studies and chemical reports following the Seveso accident, which describe transient symptoms of peripheral neuropathies in highly exposed intervals (Todd, 1962; Berkley and Magee, 1963; Goldstein et al., 1959; Boeri et al., 1978; Pocchiari et al., 1979; Filippini et al., 1981~.
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Because of its public health importance, breast cancer also receives attention. Several reproductive effects are classified in this category, including spontaneous abortion, birth defects other than spine bifida, neonatal/infant death and stillbirths, low birthweight, childhood cancer in offspring, and abnormal sperm parameters and infertility.
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From page 12... ...
Thus, there is inadequate/insufficient evidence to determine whether an association exists between exposure to herbicides and nasal/ nasopharyngeal cancer. There have been a few occupational studies, two environmental studies, and two veterans studies of breast cancer among women exposed to herbicides and/or TCDD.
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In response to the request from the DVA to explore latency issues related to herbicides used in Vietnam, the committee attempts in Chapter 8 to establish a methodology to address the timing of herbicide exposure and the risk of cancer. This chapter also reviews the literature on herbicide exposure and cancers classified in the "Sufficient Evidence of an Association" and "Limited/Suggestive Evidence of an Association" categories for results that describe how timing of exposure affects the relative risk due to exposure.
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From page 14... ...
For prostate cancer, the epidemiological literature was not informative on how long the effects of exposure last, the effect of the age at which the exposure was received, or whether the carcinogen acts at an early or late stage of the carcinogenic process. Increased Risk of Disease in Vietnam Veterans Although there have been numerous health studies of Vietnam veterans, most have been hampered by relatively poor measures of exposure to herbicides or TCDD, in addition to other methodological problems.
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