longer be fully evaluated after this update. It is unlikely, given the age of the Vietnam veteran cohort, that any newly published data on those two outcomes will provide additional information that would be directly relevant to that cohort. However, if new research suggests that the two outcomes may be influenced by epigenetic changes, their relevance to transgenerational effects will be assessed in future updates.

To reduce repetition throughout the report, Chapter 5 presented design information on new studies that report findings on multiple health outcomes. To provide context for publications that present new results on study populations that were addressed in publications reviewed in earlier updates, Chapter 5 also discussed the overall characteristics of those populations with details about design and analysis relevant to individual publications. Design information on new studies that report only reproductive health outcomes and are not revisiting previously studied populations is summarized in this chapter with results.

This chapter’s primary emphasis is on the potential adverse reproductive effects of herbicide exposure of men because the vast majority of Vietnam veterans are men. However, about 8,000 women served in Vietnam (H. Kang, US Department of Veterans Affairs, personal communication, December 14, 2000), so findings relevant to female reproductive health are also included. Whenever the information was available, an attempt was made to evaluate the effects of maternal and paternal exposure separately. Exposure scenarios in human populations and experimental animals studied differ in their applicability to our population of concern according to whether the exposed parent was a male or female veteran. In addition, for published epidemiologic or experimental results to be fully relevant to evaluation of the plausibility of reproductive effects in Vietnam veterans, whether female or male, the timing of exposure needs to correspond to the veterans’ experience (that is, it must have occurred only before conception). With the possible exception of female veterans who became pregnant while serving in Vietnam, pregnancies that might have been affected occurred after deployment, when primary exposure had ceased.

BIOLOGIC PLAUSIBILITY OF REPRODUCTIVE EFFECTS

This chapter opens with a general discussion of factors that influence the plausibility that TCDD and the four herbicides used in Vietnam could have adverse reproductive effects. There have been few reproductive studies of the four herbicides in question, particularly picloram and cacodylic acid, and those studies generally have shown toxicity only at very high doses, so the preponderance of the following discussion concerns TCDD, which outside of controlled experimental circumstances usually occurred in a mixture of dioxins (dioxin congeners in addition to TCDD).

Because TCDD is stored in fat tissue and has a long biologic half-life, internal exposure at generally constant concentrations may continue after episodic,



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