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Background Since the 1990–1991 Persian Gulf War, there has been persistent concern that U.S. war veterans may have had adverse health consequences, including higher-than-normal mortality.
Methods We conducted a retrospective cohort study of postwar mortality according to cause among 695,516 Gulf War veterans and 746,291 other veterans. The follow-up continued through September 1993. A stratified, multivariate analysis (with Cox proportional-hazards models) controlled for branch of service, type of unit, age, sex, and race in comparing the two groups. We used standardized mortality ratios to compare the groups of veterans with the general population of the United States.
Results Among the Gulf War veterans, there was a small but significant excess of deaths as compared with the veterans who did not serve in the Persian Gulf (adjusted rate ratio, 1.09; 95 percent confidence interval, 1.01 to 1.16). The excess deaths were mainly caused by accidents (1.25; 1.13 to 1.39) rather than disease (0.88; 0.77 to 1.02). The corresponding rate ratios among 49,919 female veterans of the Gulf War were 1.32 (0.95 to 1.83) for death from all causes, 1.83 (1.02 to 3.28) for accidental death, and 0.89 (0.45 to 1.78) for death from disease. In both groups of veterans the mortality rates were significantly lower overall than those in the general population. The adjusted standardized mortality ratios were 0.44 (95 percent confidence interval, 0.42 to 0.47) for Gulf War veterans and 0.38 (0.36 to 0.40) for other veterans.
Conclusions Among veterans of the Persian Gulf War, there was a significantly higher mortality rate than among veterans deployed elsewhere, but most of the increase was due to accidents rather than disease, a finding consistent with patterns of postwar mortality among veterans of previous wars.
Some 700,000 U.S. troops were deployed in the Persian Gulf area between August 1990 and the end of Operation Desert Storm in 1991. Among the potential health risks associated with military service during that conflict, infectious diseases, oil-well fires and hazards associated with other petroleum products, insecticides and pesticides, sand particles, the possible use of chemical and biologic warfare agents, anti–nerve gas agents, and multiple vaccinations have often been suggested as putative risk factors.3,4 Furthermore, the psychological stress involved in deployment to the Persian Gulf and exposure to combat has been well documented.5,6,7
On the basis of previous studies, we expected that veterans of the Gulf War would have increased mortality due to external causes, including motor vehicle accidents and accidents of other types, suicide, and homicide. Among Vietnam veterans, an elevated risk of traumatic deaths, including deaths due to motor vehicle accidents, has been often reported.8,9,10
We conducted a retrospective cohort study of mortality in which we compared the postwar mortality of Gulf War veterans with that of veterans from the era of the Gulf War who did not serve in that conflict. This study complements the study by the Department of Defense of non–battle-related deaths among Gulf War troops who remained on active duty.11
Methods
Study Subjects
The study subjects were all 695,516 military personnel who served in the Persian Gulf from August 1990 to April 1991 ("Gulf War veterans"). They were identified from a roster provided by the Defense Manpower Data Center. A control group of 746,291 military personnel consisted of a stratified random sample of approximately half of all personnel on active duty, in the National Guard, and in the military reserves who served from September 1990 to April 1991 but did not go to the Persian Gulf. The number of controls and the number of Gulf War veterans in each type of unit in each branch of the armed forces were approximately equal. In the case of controls serving in reserve and National Guard units, equal numbers were selected from units that were activated but sent to places other than the Persian Gulf area and units that were not activated at all. Personnel sent to the Persian Gulf area after the war were not included in the control group.
Available demographic information and data on military service included the veteran's date of birth, race, sex, military rank, branch of service, and deployment date, and the type of unit (active, reserve, or National Guard).
Determination of Vital Status and Collection of Death Certificates
We determined the vital status of each Gulf War veteran from the date the veteran left the Persian Gulf area. The follow-up of controls began on May 1, 1991. The follow-up period ended either on the veteran's date of death or on September 30, 1993, whichever came first. (The reporting of vital status after that date was expected to be incomplete in the national data bases available for matching in May 1994.) Vital status was determined with a data base of the Department of Veterans Affairs known as the Beneficiary Identification and Records Locator Subsystem (BIRLS). Veterans were also matched against a file of deaths reported to the Social Security Administration. In a recent study of 4300 deaths of veterans ascertained independently from states, the Veterans Affairs BIRLS data base, used in conjunction with the Social Security Administration file, reported 97 percent of deaths of Vietnam-era veterans.12
Death certificates were requested first from the Veterans Affairs regional offices and the Federal Records Centers identified in the BIRLS data base. Death certificates not found at these locations were requested from state vital-statistics offices. Causes of death were coded by a qualified nosologist who used the International Classification of Diseases, 9th Revision (ICD-9), without knowing the subject's deployment status.13
The degree of completeness of the combined data sources (the BIRLS data base and the files of the Social Security Administration) used in the determination of vital status was evaluated by matching a random sample of 15,000 Gulf War veterans and 15,000 other veterans with the National Death Index, which includes all deaths reported to the National Center for Health Statistics by state vital-statistics offices, beginning in 1979.
Statistical Analysis
The data were analyzed in three stages. In stage 1, for each Gulf War veteran the number of person-years at risk of dying were counted from the date the veteran left the Persian Gulf area to the veteran's date of death or September 30, 1993. For the controls, this period at risk began on May 1, 1991. The relative frequency of death overall, as well as death due to specific causes, was compared between the Gulf War veterans and the controls on the basis of the number of person-years at risk. Unadjusted rate ratios were calculated from the crude death rates.
In stage 2, the Cox proportional-hazards model was used to account for possible confounding and the effect of selected covariates on the risk of a veteran's dying from a specific cause, according to the time since that veteran's entry into the cohort.14 The covariates considered in the model included age at the start of follow-up, race, sex, service branch, and type of unit.
In stage 3, the cause-specific mortality of Gulf War veterans and other veterans was compared with the number of deaths expected in the overall U.S. population after adjustment for age, sex, race, and year of death. The results were expressed as standardized mortality ratios15 expressing the ratio of observed deaths among veterans to the expected number of deaths in the general population.
Results
Characteristics of the Two Groups
The demographic and military characteristics of the Gulf War veterans were similar to those of the controls with the exception of the year of birth, sex, and type of unit (Table 1). The Gulf War veterans were slightly younger than the controls (age in May 1991, 28.4 vs. 30.2 years), included more troops serving in active units, and included fewer women (7.2 percent vs. 13.3 percent). Among reservists and members of the National Guard who did not take part in the Gulf War, the characteristics of 106,840 veterans who were mobilized and 115,478 veterans who were not were similar.
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Cause-Specific Mortality
As Table 2 shows, after we controlled for potential confounders (age, sex, race, and military variables), the Gulf War veterans had significantly higher mortality from all causes than the other veterans. The excess deaths were entirely attributable to external causes (rate ratio, 1.17; 1317 deaths observed vs. 1126 expected), including all types of accidents and motor vehicle accidents specifically. There was no observed excess of suicides, homicides, or deaths from disease-related causes. The risk of death from infectious and parasitic diseases was significantly lower among the Gulf War veterans than among the other veterans.
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Cause-Specific Mortality According to the Time of Deployment to the Persian Gulf
Troops sent to the Persian Gulf before March 1, 1991, would have been subjected to most of the potential risk factors previously described. Troops deployed after the war ended (that is, after March 1, 1991) would not have taken anti–nerve gas agents (pyridostigmine bromide) or received vaccinations against anthrax and botulinum toxins. Nor would they have been subjected to the threats of Scud missile attacks, chemical and biologic warfare, or combat-induced stress. There was no significant difference among Gulf War veterans in the risk of death from any of the underlying causes studied according to period of deployment.
Effect of Mobilization
We studied the effect of being mobilized without being actually sent to the Persian Gulf area in 222,318 veterans assigned to units in the reserves and the National Guard. Mobilization without subsequent deployment to the Persian Gulf did not appear to affect the overall mortality or the risk of death from external causes, even after adjustment for the type of unit (reserve or National Guard), age, sex, race, and branch of service.
Comparison with the General Population
As compared with the general population of the United States, the Gulf War veterans and the non–Gulf War veterans both had significantly lower cause-specific standardized mortality ratios (Table 4). Deaths among both groups of veterans occurred at a rate no more than half that expected in the U.S. population after adjustment for age, sex, race, and year of death.
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Being mobilized without actually serving in the Persian Gulf area appears to have affected the mortality rates of women more than those of men. Among 31,814 female study subjects who served in the reserves or the National Guard and who did not serve in the Gulf War, 17,270 were mobilized and deployed somewhere (for example, in Germany), and 14,544 were not mobilized at all. Women who were deployed somewhere had a higher, but not a significantly higher, rate of death from all causes than nonmobilized women (rate ratio, 1.94; 95 percent confidence interval, 0.92 to 4.07), a higher rate of death from external causes (1.81; 0.73 to 4.5), and a higher rate of death from accidents (3.0; 0.6 to 15) after adjustment for the type of unit, age, race, and branch of service.
Female Gulf War veterans had a higher (but not significantly higher) risk of death from external causes, including accidents, than their female peers in the general U.S. population (Table 4). The rate of death due to motor vehicle accidents among the female Gulf War veterans was 43 percent higher than expected, whereas among other female veterans the risk was 31 percent lower than expected.
Discussion
The purpose of this study was to assess the effect of service in the Persian Gulf War on mortality among veterans of U.S. military service. Gulf War veterans have had a significantly higher mortality than other veterans who served during the same period. Accidental deaths accounted for most of this increase. Neither the suicide rate nor the homicide rate was elevated among Gulf War veterans. Mortality due to illness was not higher in Gulf War veterans than in other veterans. Of the 10 deaths attributed to infectious or parasitic disease, none were reported as due to leishmaniasis or other infectious diseases endemic to the Middle East, or as due to the effects of biologic warfare agents. If there are excess illnesses due to Persian Gulf service, they do not appear to have been life-threatening.
The significant excess mortality from external causes among Gulf War veterans as compared with controls is similar to what has been observed in studies of veterans of other wars. Studies of Vietnam veterans repeatedly found an increased risk of traumatic deaths, mainly from accidents.8,9,10 The Department of Defense study of Gulf War veterans who remained on active duty found 225 non–battle-related deaths, including 183 deaths from injuries, through July 1991 (five months after the war began), whereas 202.7 and 118.6 deaths, respectively, were expected on the basis of the rates among other veterans serving at the same time.11
The underlying reasons for the excess of deaths due to external causes among war veterans are not well understood. One may speculate that survivors of war perceive the degree of risk in any given situation differently from others and may therefore engage in more risk-taking behavior. Another possibility is that those in combat may be at increased risk for post-traumatic stress disorder or other depressive disorders, which in turn contribute to the excess number of deaths due to trauma.5,6,7,16,17,18
That there were fewer deaths among veterans than were expected from mortality rates in the U.S. population is consistent with the findings of studies of many other military populations. This "healthy-soldier effect" is similar to a healthy-worker effect. Because of the initial physical screening for military service, requirements to maintain a certain standard of physical well-being, and better access to medical care during and after military service, a military cohort almost always has better survival rates than a comparable segment of the general population. A recent study of all soldiers in the U.S. Army who were on active duty in 1986 found that the mortality of soldiers was only half that of their civilian counterparts.19
Serious flaws in the design and execution of the study are an unlikely explanation for our findings. To minimize statistical variation due to sampling, the study included all Gulf War veterans and almost half of all military personnel who were not sent to the Persian Gulf. Given the large sample and the 2.4-year period of follow-up, the statistical power of the study would be about 80 percent to detect a 10 percent increase in overall mortality and almost 100 percent to detect a 20 percent increase (by a two-tailed test with a type I error of 0.05).20 In the analysis of deaths from all external causes combined, the power would be about 60 percent to detect a 10 percent increase, but 99 percent to detect a 20 percent increase. For accidental deaths, the statistical power would be about 90 percent to detect a 20 percent increase, and almost 100 percent to detect a 50 percent increase.
Because of the healthy-soldier effect, a moderate increase in the risk of death would not have been detected in a population of recent veterans, had we compared our findings only with the U.S. population. The results would be unlikely to change substantially if data from missing death certificates were added. Vital status was ascertained at an estimated rate of 89 percent (95 percent confidence interval, 83 to 97 percent) in relation to the National Death Index, with no significant difference between Gulf War veterans and other veterans in the proportion whose vital status was unknown. Among veterans who died, the cause of death was known for 93.7 percent of those who served in the Gulf War and 93.4 percent of those who did not.
The interpretation of the study findings is somewhat confounded by the possibility that military personnel who were seriously ill or recovering from major surgery would not have been deployed to the Persian Gulf area. How much this potential selection bias has contributed to the favorable outcomes with regard to mortality from disease-related causes in veterans of the Gulf War is unknown.
Another limitation of the study is our reliance on death certificates rather than medical records for information on causes of death. Death certificates dependably establish the fact of a person's death, but their accuracy in recording the cause is variable.21 However, in reporting external causes of death the agreement between medical records and death certificates has been reported to be good.8 A further possible limitation is the lack of data on potential risk factors, such as a history of smoking, a history of drinking, and preexisting mental disorders. Any such factors may have been present in equal degrees in the two groups, because the men and women were all accepted into the military before the war and in almost all instances deployment to the Persian Gulf was not voluntary.
The effect of the Gulf War on postwar mortality appears to be greater among female veterans. Both male and female veterans of the conflict had higher rates of mortality from external causes than the controls, but the increase was greater among women. In contrast, there was no excess of deaths from disease among either male or female Gulf War veterans. Mobilization without actual service in the Persian Gulf area had no substantial effect on the mortality of Gulf War veterans as a group. Among women, however, those who were mobilized had a higher risk of death from each category of external causes than those who were not mobilized, although the risk was not significantly higher.
More of the troops deployed to the Persian Gulf War were women (7 percent) than in any previous war. By contrast, women made up less than 0.5 percent of Vietnam veterans.10 The increase in the number of women in the military and their expanding role in combat-related activities mean that their health must be monitored carefully. Furthermore, a substantial portion of the women sent to the Persian Gulf area (45 percent) were married at the time, and some of them left small children at home to be cared for by others. The effect of this added psychological stress associated with deployment and redeployment warrants further study.
In summary, as compared with non–Gulf War veterans, veterans of the conflict in the Persian Gulf had significant excesses of death from external causes (mainly accidents) but not from disease-related causes. Their risk of death remained less than half that expected in their civilian counterparts. Our findings are consistent with the postwar mortality observed in veterans of previous wars.
Supported by funds from the Medical Research Service, Office of Research and Development, Department of Veterans Affairs.
We are indebted to Dr. Eula Bingham and the members of the Persian Gulf Expert Scientific Committee of the Department of Veterans Affairs for their review of the study protocol, and to Mr. Mike Dove and Ms. Sue Butler of the Defense Manpower Data Center for assistance with the identification and selection of study subjects.
Source Information
From the Department of Veterans Affairs, Environmental Epidemiology Service (135), 1120 20th St., NW, Washington, DC 20036-3406, where reprint requests should be addressed to Dr. Kang.
References
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