estimate exposures to sarin and cyclosarin, but it is difficult to incorporate intelligence information, meteorologic data, transport and dispersion data, and troop-unit location information accurately (see Volume 4, Chapter 2, Exposures in the Persian Gulf). Extensive efforts have been made to model and obtain information on potential exposures to DU, smoke from oil-well fires, and other agents. Although modeling efforts are important for discerning the details of exposures of Gulf War veterans, they require external review and validation. Furthermore, even if there were accurate troop location data, the location of individual soldiers would be very uncertain. Because of the limitations in the exposure data, it is difficult to determine the likelihood of increased risk for disease or other adverse health effects in Gulf War veterans that are due specifically to biologic and chemical agents.

Although many studies have assessed military personnel exposures to various preventive agents including PB and pesticides during the Gulf War, these studies have been based on individuals’ recall of the measures they received or took, frequently under stress situations, and have rarely been verified by in situ measurements or records. This potential for recall bias also contributes to the difficulty in identifying specific causes of the veterans’ health problems.

Individual Variability

Differences among people in their genetic, biologic, psychologic, and social vulnerabilities add to the complexities in determining health outcomes related to specific agents. People with increased sensitivity to some agents will have different health outcomes than people who are less sensitive. For example, a person who is a poor metabolizer of a particular substance, depending on his or her genetic makeup, might be at higher or lower risk for specific health effects if exposed to the substance. For example, researchers are investigating the genotypes that code for two forms of an enzyme that differ in the rate at which they hydrolyze particular organophosphates (including sarin) (Costa et al., 1999). Lower hydrolyzing activity would mean that despite identical exposure to sarin, more sarin would be bioavailable in people who are poor metabolizers and could result in increased anticholinesterase effects. See Appendix A for a discussion of the metabolism of chemical agents.

VOLUME 4 CONCLUSIONS

In Gulf War and Health, Volume 4 (IOM, 2006b), no associations were found between being deployed to the Gulf War and any health effects, nor were any associations found between specific exposures that may have occurred during deployment and health effects. The committee that prepared that volume, however, did report that Gulf War veterans, regardless of the country they served, consistently reported higher rates of nearly all symptoms examined than their nondeployed counterparts. This was true for veterans from the United States, the United Kingdom, Canada, Australia, and Denmark. The Volume 4 committee found that the majority of studies of Gulf War veterans relied on self-reports of symptoms and medical conditions. Fewer studies used objective measures or diagnostic medical tests to confirm the veterans’ reports. The committee recognized that many of the veterans symptoms were subjective—for example, headache, joint pain—and could not be evaluated other than by self-report, but other symptoms and medical conditions—for example, fibromyalgia, irritable bowel syndrome—had diagnostic criteria or laboratory tests that could be used to make or verify a diagnosis. Therefore, the Volume 4 committee grouped the health effects in Gulf War veterans on the basis of whether the



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