The mental health of UK Gulf war veterans: phase 2 of a two phase cohort study

Introduction

Population based studies have consistently found that veterans of the 1990-1 Persian Gulf conflict report symptoms around two to three times more often than appropriate controls. 1 2 The symptoms reported are multisystem and non-specific such as fatigue, sleeping difficulties, and irritability, which at present are medically unexplained. Markers of serious physical morbidity, such as admission to hospital and mortality, are not increased in Gulf veterans, with the exception of accidents. 3 4 Complex multivariate statistical analyses have failed to identify a cluster of symptoms, conditions, or causal factors consistent with a new syndrome.5

Common psychiatric disorders also seem to be increased in Gulf veterans. Depression, tension headache, and post-traumatic stress disorder accounted for a major proportion of clinical diagnoses in voluntary registers, but these were likely to have been over-represented by veterans who perceived themselves as ill.6Population based studies have also shown that symptoms of depression and post-traumatic stress disorder are reported more commonly in Gulf veterans, but self reported symptoms may over-estimate or underestimate psychiatric morbidity and have poor concordance with clinician ratings. 1 2 7 8

In civilian populations, medically unexplained symptoms are associated with increased rates of psychiatric disorders.9 This may also be the case in Gulf veterans.10 An association was found between number of symptoms and post-traumatic stress disorder and depression in one sample of US Gulf veterans by using structured psychiatric interviews, but a control group of non-Gulf veterans was not used to test whether this was unique to the Gulf experience.11

The nature of ill health in Gulf veterans remains unclear. We aimed to test the strength of the association between psychiatric disorders and reported ill health in Gulf veterans. We also aimed to test whether psychiatric disorders in Gulf veterans who reported ill health were more common than in non-Gulf veterans with similar levels of ill health.

Participants and methods

Design

We used a two phase study design. Phase 1 was a population based survey using a postal health questionnaire to compare self reported health indices in three randomly selected cohorts of the UK armed forces. The cohort of interest was those deployed to the Gulf conflict between 1 September 1990 and 30 June 1991 (n=5 046). We chose two cohorts as controls: one comprised veterans who served in Bosnia as part of the United Nations peacekeeping forces between 1 April 1992 and 6 February 1997 (n=3450) to match for the experience of being in an international conflict, and the other comprised veterans who were in active service in the UK armed forces during the Gulf conflict but not deployed to the Gulf (Era veterans; n=4248) to match for military experience. The methods, response rates, and main findings of phase 1 have been published elsewhere.7 In phase 2, reported here, we compared Gulf veterans who screened positive at phase 1 for physical disability with Gulf veterans who screened negative and with Bosnia and Era veterans who screened positive (figure).

Study design. *Includes 800 Bosnia veterans from Bosnia sample who had also been deployed to the Gulf and for all subsequent analyses were taken as part of Gulf cohort

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Results

Overall, 740 cohort members were eligible for the study. Contact was made with 607. Non-participants were defined as those who refused to participate (n=176) and those who initially agreed to participate but did not attend (n=89). Table 2 compares the characteristics of participants with non-participants. The participation rate from phase 1 to phase 2 was 67% (n=111) for disabled Gulf veterans, 62% (n=98) for non-disabled Gulf veterans, 55% (n=54) for disabled Bosnia veterans, and 43% (n=79) for disabled Era veterans (figure).

Table 3 details the sociodemographic and military characteristics of participants in the four groups (Bosnia and Era reported separately). Distributions for sex and marital status were similar across the groups. Disabled veterans were more likely to be older than non-disabled veterans, to have left the armed forces, and to belong to a lower rank. Phase 2 scores on the SF-36 physical functioning subscale showed that between a third to a half of disabled veterans at phase1 had improved whereas around 10% of non-disabled (Gulf only) veterans at phase 1 now met the criteria for disability.

The summary statistics for probability weights in table 1 show that the non-disabled Gulf veterans had the largest probability weights because there were relatively more of them in phase 1 than there were of disabled Gulf and non-Gulf veterans (figure). The combined inter-rater reliabilities for depressive disorders (κ coefficient 0.83) and anxiety disorders (κ coefficient 0.85) were high.

Table 4shows the distribution of current DSM-IV categories and disorders. Most psychiatric disorders were 2-10 times more common in disabled Gulf veterans than they were in non-disabled Gulf veterans except for alcohol related disorders, which were less common. The rates for most psychiatric disorders were similar between disabled Gulf veterans and disabled non-Gulf veterans (Bosnia and Era veterans combined) except for somatoform disorders, which were twice as common in the disabled Gulf group. The rates for post-traumatic stress disorder were similarly low in all three groups.

The likelihood of having any psychiatric disorder in each DSM-IV category was assessed by logistic regression (table 5). Disabled Gulf veterans were significantly more likely to have depressive, anxiety, somatoform, and sleep disorders than were non-disabled Gulf veterans. Any common psychiatric disorder (depression, anxiety, and alcohol related disorders) was around two and half times more common in disabled Gulf veterans than it was in non-disabled Gulf veterans.

Comparing the risk of psychiatric disorders between disabled Gulf veterans and disabled non-Gulf veterans (Bosnia and Era veterans combined) showed no significant differences after adjusting for confounding except for somatoform disorders, which were three times more likely in the disabled Gulf veterans (table 5). The relative rate for any common psychiatric disorder (depression, anxiety, and alcohol related disorders) was not significantly greater in disabled Gulf veterans compared with disabled non-Gulf veterans.

Discussion

The validity of previous research into the nature of ill health of Gulf veterans has been questioned because of the lack of appropriate controls and the use of self reported measures. In this observational study we used standardised clinician ratings to measure psychiatric disorder in randomly selected samples of Gulf veterans and non-Gulf veterans (Bosnia and Era veterans combined). We found a negative association: three quarters of Gulf veterans with disability do not have formal psychiatric disorders, such as depression, anxiety, or alcohol related problems, although the prevalence was more than double that of Gulf veterans with no (or minimal) disability. We also found that disabled Gulf veterans are not much different in their pattern of mental health problems to similarly disabled non-Gulf veterans except that they have a threefold increase in somatoform disorders. The prevalence of post-traumatic stress disorder was no different in the three groups, suggesting that whatever the nature of ill health in Gulf veterans, it was not explained by events or exposures conventionally understood to be psychologically traumatic.

Several potential limitations to our study need to be considered. Firstly, we used a two phase cohort design as an efficient method of identifying the most ill and most healthy veterans when there is no case definition for ill health in Gulf veterans.15 Using a screening questionnaire alone would be prone to reporting bias. A clinical interview of thousands of veterans would have been too costly. The limitation of a two phase design is that conclusions are made on a small proportion of the population being studied so that the overall estimate of the associations are less precise. We used sampling weights to take account of different probabilities for being selected based on cohort status and physical functioning, but this would not have corrected for response rates at phases 1 and 2.

Secondly, a sizeable proportion of disabled veterans at phase 1 had improved physical functioning by the time they participated in the clinical interview at phase 2, whereas a smaller proportion of healthy Gulf veterans became worse. This may have led to an underestimation of current psychiatric disorders in disabled Gulf veterans. By using a physical functioning measure to define ill health we may have overidentified people with physical symptoms and underidentified people with psychological symptoms. However, using psychiatric screening measures such as the general health questionnaire would have biased the study to overestimating psychiatric disorders.16

The prevalence of common psychiatric disorders are not increased in Gulf veterans who report no physical disability, and it is reassuring that even in those selected by their level of disability the rates are not substantially increased. These findings contrast with most previous research, which has used self report measures.1 The increase in somatoform disorders that we found should be treated cautiously. Although it confirms that there is an increase in symptomatic distress in Gulf veterans, redefining medically unexplained symptoms as somatoform disorders may to some extent be tautological and is anyhow a controversial psychiatric disorder. Most somatoform disorders were of the undifferentiated type, a diagnosis that falls short of somatisation disorder, which is the more severe and rare form. Undifferentiated somatoform disorder described here represents multiple unexplained symptoms that are distressing but not so severethat Gulf veterans are seeking multiple medical advice or reassurance to establish their cause.

We found low rates of post-traumatic stress disorder, which contrasts with most other studies. Several studies have used self reported measures, which may have overestimated post-traumatic stress, or have used selected samples. 1 11 17 Our findings also contrast with studies that found a positive association between symptoms of post-traumatic stress and ill health in Gulf veterans.17 One interpretation is that a simple association between ill health and the conventional diagnosis of post-traumatic stress disorder is not necessarily found in modern military populations, especially in conflicts such as the Gulf war in which traditional military combat trauma was rare. We suggest that current models of psychological distress based solely on discrete traumatic events may have limited explanatory function in Gulf related ill health and that other vulnerability factors such as the effects of premorbid health, media reporting, and communication of risk may have a more important role in explaining anxiety and somatic symptoms in Gulf veterans. Other methodological explanations may exist for the low rates of post-traumatic stress disorder. In our study non-participants in phase 2 had more psychological distress at phase 1, and it is possible that some veterans with post-traumatic stress disorder were too ill to attend for phase 2.

We continue to find an effect of the Gulf conflict manifested as increased symptomatic distress. In our study, the modest increase in psychiatric disorders do no fully explain ill health in Gulf veterans.