signs (most important, cohort, case–control, and cross-sectional) have strengths and weaknesses (see Chapter 2) that influence their potential to contribute evidence considered in the health-outcomes chapters.
The second part of this chapter provides design information on populations that are the subjects of multiple references in this and earlier VAO reviews, including new studies of populations that have been studied previously and studies of new populations with multiple health outcomes, to avoid repeating design information in multiple health-outcomes chapters. (The design information on studies of new populations that involve single health outcomes is provided in the various health-outcomes chapters.) For presentation of the background information, the study populations are arranged into the categories based on whether they are composed of Vietnam veterans, occupationally exposed workers, or environmentally exposed individuals or were assembled according to a case–control approach focused on particular health outcomes.
In addition to reviewing studies involving exposures to the specific chemicals of interest listed previously, this and earlier VAO committees have also considered studies that examined compounds chemically related to the herbicides used in Vietnam, such as 2-(2-methyl-4-chlorophenoxy) propionic acid, hexachlorophene, and chlorophenols, particularly 2,4,5-trichlorophenol. Some publications did not indicate the specific herbicides to which study participants were exposed or the magnitude of exposure; those limitations were considered when the committee weighed the relevance of each publication, as detailed in Chapter 2. The committee also considers studies of exposure to polychlorinated biphenyls (PCBs) and other dioxin-like compounds (DLCs) informative if their results were reported in terms of TCDD toxic equivalents (TEQs) or concentrations of specific congeners of DLCs. Available details of exposure assessment and use of the resulting data in analyses are discussed in Chapter 3, which follows the same sequence to categorize study populations.
The new epidemiologic publications reviewed by the committee for this update are listed in Tables 5-1, 5-2, and 5-3. The conditions listed in the “Health Outcomes reported” column are indicative of the chapters in which the new publications are considered. Note, however, that studies assessing the occurrence of various cancers following exposure scenarios temporally comparable to exposure during military service are discussed in Chapter 7, which addresses cancer outcomes in the veterans themselves. Studies of childhood cancers in relation to parental exposure to the chemicals of interest are discussed in Chapter 8, which addresses possible adverse effects in the veterans’ offspring. Cancer studies that consider only childhood exposure are not considered relevant to the committee’s charge.