Summary

Military personnel may be exposed to many environmental and occupational hazards during deployment to a combat zone, including emissions from fuel and exhaust from jet and diesel engines, airborne dust and sand, solvents, radiation, and open burn pits. They have reported health problems after returning from deployments; they have also expressed concerns that these issues may arise from exposures during deployment. Studies have shown that some of these health problems are linked to deployment exposures, but most of this research has focused on physical health effects. Less is known about the relationship between environmental and occupational exposures during deployment and mental, behavioral, and neurologic conditions.

As directed in Section 507 of PL 117-168, Sergeant First Class Heath Robinson Honoring our Promise to Address Comprehensive Toxics Act of 2022 (PACT Act), the Department of Veterans Affairs (VA) contracted with the National Academies of Sciences, Engineering, and Medicine to convene an ad hoc committee to assess possible relationships between environmental and occupational exposures during military service and mental, behavioral, and neurologic health conditions and chronic multisymptom illness (CMI). The committee was tasked with conducting an independent scientific assessment using information from Veterans Health Administration (VHA) health care records and other administrative records, which Congress directed VA to provide to the committee. At VA’s request, the report includes findings and conclusions but no recommendations. Box S-1 provides the complete Statement of Task.

The committee held three information-gathering sessions. The first focused on input on its Statement of Task. The second was held to learn about potential VA and Department of Defense (DoD) data sources. At the third, the committee heard from veterans, advocates, and mental health providers to learn about veterans’ mental health problems, CMI, and concerns about military exposures. These sessions were immensely helpful in informing the committee’s deliberations around identifying and defining relevant exposures and outcomes and appropriate sources of data for its analyses.

Consistent with the focus of the PACT Act, VA asked the committee to focus its assessment on veterans who deployed to the Southwest Asia Theater of Operations¹ or Afghanistan and served in post-9/11 conflicts;² thus, the committee interpreted “toxic exposures” to refer to military-related environmental and occupational exposures during deployment to this region after September 11, 2001. In civilian settings, environmental exposures are generally low-level, long-term hazardous exposures encountered in daily life, whereas occupational exposures are hazardous exposures experienced at or while doing work. Because service members live and work in the same or nearby locations during deployment, exposures experienced during military deployment combine these two types of exposures.

The committee investigated 16 health outcomes, of which 10 were specified in the Statement of Task (see Box S-1). VA directed the committee to focus on new diagnoses in its assessment and not on symptom severity or exacerbation. For the category of neurocognitive disorders, the committee included dementia and added amyotrophic lateral sclerosis (ALS), Parkinson’s disease, and multiple sclerosis (MS), which can include changes in cognition. In addition to attention-deficit/hyperactivity disorder (ADHD), the committee added attention-deficit disorder (ADD),³ since attention disorders often present without hyperactivity in adults, to create a group of attention disorders. The committee requested but did not receive data on suicide deaths, but it was able to investigate nonfatal suicide attempts and intentional self-harm. The committee added anxiety disorders, adjustment disorders, sleep disorders, and substance use disorders (SUD) to the

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¹ This includes Iraq, Kuwait, Saudi Arabia, the neutral zone between Iraq and Saudi Arabia, Bahrain, Qatar, the United Arab Emirates, Oman, the Gulf of Aden, the Gulf of Oman, the Persian Gulf, the Arabian Sea, the Red Sea, and the airspace above these locations.

² These operations include Operation Enduring Freedom (October 7, 2001–December 28, 2014); Operation Iraqi Freedom (March 19, 2003–August 31, 2010); Operation New Dawn (September 1, 2010–December 15, 2011); Combined Joint Task Force–Operation Inherent Resolve (October 17, 2014–present [as of August 2025]); and Operation Freedom’s Sentinel (January 1, 2015–August 31, 2021).

³ ADD was removed in prior versions of the Diagnostic and Statistical Manual of Mental Disorders and is no longer used for diagnosis. However, it is still used in common parlance and International Classification of Diseases, Tenth Revision (ICD)-10 codes for both ADHD and ADD are included in the analyses.

10 mandated outcomes because of known or perceived interest in their etiology among post-9/11 veteran communities. Although traumatic brain injury (TBI) is included in the committee’s charge, because it is defined as resulting from an external force, the committee included TBI as a covariate in stratified analyses to understand the likelihood of developing a specific condition among those with and without a TBI diagnosis.

The committee used health outcome and other administrative data from VHA linked to exposure data from the Individual Longitudinal Exposure Record (ILER), a joint VA and DoD platform that compiles data from multiple sources to document a service member’s or veteran’s military exposure history, for its original data analysis. The exposure data include environmental monitoring data that are collected by environmental science and engineering officers and industrial hygiene data on workplace hazards. The linked data were composed of post-9/11 veterans who received a diagnosis at VHA during 2017–2023 and had a record in ILER. This dataset comprised 1,145,301 veterans, of whom 960,128 had records indicating exposure to at least one of the exposures of interest: burn pits (including burn pits, burn barrels, and burning landfills), dust and particulate matter (PM, also including specific pollutants), diesel and jet exhaust, diesel and jet fuels, incinerator emissions, metals (including aluminum, hexavalent chromium, lead, depleted uranium, and manganese), mold, radiation, and solvents. The majority had three distinct exposures. Compared to other veterans with VHA health encounters in the same period, the committee’s sample population was younger, was more racially and ethnically diverse, had higher rates of disability, and included more female veterans.

The committee used these data to conduct case-control studies on the possible relationship between each exposure and outcome. It selected this design because of the short outcome window and rare outcomes, it is more computationally efficient, and its statistical results are easily interpretable. Sample sizes for each case-control study depended on the number of cases and up to four controls matched on age at encounter, sex, and year enrolled in the Veterans Benefits Administration. Cases were defined as VA health care users who had an International Classification of Diseases (ICD)-10 recorded diagnosis of one of the outcomes of interest received in either inpatient or outpatient VA settings during 2017–2023. This approach is appropriate for the short and recent outcome window, because outcomes are rare and it is likely to capture all possible cases, which is consistent with the committee’s charge to broadly assess possible relationships. Additionally, diagnoses for some of these rare outcomes like schizophrenia are likely to be retained in a patient’s record after just one diagnosis because receiving a diagnosis requires relatively severe and persistent presentation. Controls were individuals with an ILER exposure record who used VHA health care in the same period but did not have the outcome diagnosis. The committee applied conditional logistic regression models to estimate

odds ratios among matched cases and controls. Numerous factors in addition to deployment-related environmental and occupational exposures can contribute to the risk of developing mental, behavioral, and neurologic health outcomes, such as demographics, genetic profile, adverse childhood experiences, and traumas experienced during military service like sexual or combat trauma. Some of these factors were incorporated into its analysis when data were available; for example, adjusted models accounted for race, ethnicity, and service branch in addition to the matching characteristics.

The committee recognizes many limitations inherent in its legislatively required analysis, which primarily arise from shortcomings in the quality and availability of the data it was required to use. The study sample only generalizes to the population of veterans who have a recorded exposure in ILER, separated from the military, and received VHA health care during 2017–2023. It does not generalize to all post-9/11 service members or veterans, including those who are still in the military. Other limitations relate to the measurement of exposure and outcome and data gaps. Limitations related to exposure measurement include only having data from ILER, which are incomplete, periodic, and inconsistent; mostly capture broad sources of exposure rather than specific measured toxicants; and do not contain reliable information on concentration, duration, and frequency. In addition, although ILER was developed to provide person-level exposure data, the data are recorded at the area level and assigned to individuals, which may misclassify a person as exposed or not and does not permit assessments of an individual’s risk of a condition. Limitations related to outcome measurement include misdiagnosis or inconsistent diagnosis in the electronic health records due to underdiagnosis, overdiagnosis, and differences in how diagnoses are coded. Data gaps include having no data on potential confounders such as preexisting conditions or trauma exposures that can influence the ability to observe the true relationships among the exposures and outcome. These limitations of the measures could magnify or attenuate the observed exposure–outcome relationship.

After considering multiple statistical measures and its assessment of the likelihood of the influence of random and systematic error on its confidence in its results, the committee chose to highlight outcomes with a point estimate threshold of 1.10 or greater in which the 95% confidence interval excluded 1.0 in the adjusted models. These criteria allow the committee to mitigate the possibility of erring when interpreting the analysis results due to the limitations of the underlying data while also allowing it to capture possible associations. Only positive (risk-conferring) associations that meet this threshold are discussed; statistically significant point estimates less than 1.0 are not described because the committee chose to focus on identifying signals of potentially meaningful risk-conferring relationships.

In recognition of the limitations of the data quality and availability and relying on any singular analysis and thus to facilitate a more holistic assessment of each possible relationship, the committee supplemented its original data analyses with a structured literature review limited to studies published in peer-reviewed, English-language journals in the last 10 years. This strategy was considered appropriate since the committee was not tasked with conducting a systematic review and weight-of-the-evidence assessment of the published literature. Rather, the literature review was used as supporting evidence to contextualize the statistical findings from its analyses.

Due to the congressionally imposed timeline, the committee initiated its literature search before receiving the exposure data and completed the review in parallel to receiving and analyzing the data for efficiency. Therefore, the committee deliberated on potential search terms without knowing the exposure categories available in ILER. The exposures for the literature review were burn pits, PM, fuels, metals, mold, radiation, and solvents. The committee assessed exposure to dust and PM, exhaust, and incinerator emissions in its statistical analyses, but it relied on literature on PM, a component of these exposures, to complement its analytic results. It decided not to conduct additional searches on dust, exhaust, and incinerator exposure after accessing the ILER data for three reasons: (1) PM is a major component of these exposures, (2) the relative robustness of the literature on PM and the outcomes compared with what the committee anticipated would be available on those three exposures, and (3) time constraints after receiving the data.

Owing to the paucity of literature on military-specific and military-related exposures and the health outcomes of interest, the committee chose to include analogous literature on environmental exposures in general populations and on nonmilitary occupational exposures. The committee recognizes that this civilian literature may have limited relevance to military exposures because the chemical composition, intensity, frequency, and duration of military and civilian exposures may differ. Moreover, extrapolating literature from the general population to the military may not capture the complexity of the military experience, which may include exposure to chemical mixtures and unique stressors.

To draw overall conclusions about possible relationships between each exposure and outcome, the committee compared its analytic findings with the results of the literature review. Literature on PM was used to support analytic results on exposure to dust and PM, exhaust, and incinerator emissions. Therefore, literature refers to PM and data analyses refer to dust and PM. For each exposure–outcome association, the evidence from the epidemiologic literature may or may not align with the committee’s findings. The committee considered four possible hypothetical scenarios of consistency of findings between its original data analyses and the literature,

in terms of both strength and magnitude of the observed association, and determined whether a given exposure and outcome had a possible risk-conferring relationship, meaning that a link may exist between the exposure and developing the health outcome. For each scenario, the committee classified a possible relationship into one of two conclusions. The committee concluded that there was a possible risk-conferring relationship between a given exposure and a given outcome if (1) both the evidence from the analyses and the epidemiologic literature showed possible risk-conferring relationships; (2) the evidence from the analyses showed a possible risk-conferring relationship and the literature was mixed, unclear, or otherwise inconclusive; or (3) the evidence from the analyses did not show a possible risk-conferring relationship, but the literature offered suggestive evidence. The committee concluded there was inadequate or insufficient evidence of a possible risk-conferring relationship between a given exposure and outcome if both the analyses and the literature did not show evidence of a possible risk-conferring relationship.

Table S-1 summarizes the committee’s conclusions by health outcome and level of evidence. Conclusions relying on the data analyses alone or together with the literature refer to dust and PM, exhaust, and incinerator emissions, whereas conclusions that possible risk-conferring relationships exist relying solely on the literature refer to PM alone. The committee did not make conclusions about whether inadequate or insufficient evidence of a possible risk-conferring relationship exists based on the literature alone, so there are no conclusions of inadequate or insufficient evidence for PM alone. The committee concluded that possible risk-conferring relationships exist between dust and PM, exhaust, incinerator emissions, PM alone, or solvents and specific mental, behavioral, and neurologic outcomes and CMI. The committee concluded that evidence is inadequate or insufficient for a possible risk-conferring relationship between burn pits, fuels, metals, mold, or radiation and any examined outcomes. A possible risk-conferring relationship existed between at least one exposure and 12 outcomes (adjustment disorders, depression, posttraumatic stress disorder, a composite measure of schizophrenia and psychosis, sleep disorders, SUD, nonfatal suicide attempts and intentional self-harm, ALS, dementia, MS, Parkinson’s disease, and CMI). The Annex to this Summary lists the committee’s full conclusions comprehensively.

The committee was tasked with assessing possible relationships between mental, behavioral, and neurologic outcomes and CMI and toxic exposures experienced during post-9/11 military service. Based on its original analyses of DoD and VA data and a structured review of the literature on possible relationships between 135 pairs of exposures and outcomes, the committee concluded that possible risk-conferring relationships exist between 24 of these pairs. For the remaining exposures and outcomes, the committee

concluded that the evidence was inadequate or insufficient. The statistical analyses have key limitations related to the quality and availability of the data that influence the committee’s confidence in its findings and ability to generalize its results beyond service members and veterans who were deployed to the Southwest Asia Theater of Operations or Afghanistan after September 11, 2001, and received care through VHA. Person-level exposure data that are systematically collected include information on exposure frequency, duration, and concentration; health outcome data that include symptom-based measures and capture care beyond VHA; and data on potential confounding factors such as prior traumas or mental health conditions would allow for more precise and accurate estimates of the relationships between adverse military exposures and mental, behavioral, and neurologic outcomes and CMI.