Headache disorders in the millennium cohort: epidemiology and relations with combat deployment.

OBJECTIVE Characterize migraine and other headache disorders within a large population-based US military cohort, with an emphasis on the temporal association between military deployment and exposure to combat. BACKGROUND Little research has been published on the prevalence of headache disorders in the US military population, especially in relation to overseas deployments and exposure to combat. A higher than expected prevalence of migraine has previously been reported among deployed US soldiers in Iraq, suggesting an association. Headache disorders, including migraine, could have important effects on the performance of service members. METHODS A total of 77,047 US active-duty, Reserve, and National Guard members completed a baseline questionnaire between July 2001 to June 2003 for the Millennium Cohort Study. Headache disorders were assessed using the following survey-based measures: self-reported history of provider-diagnosed migraine, recurrent severe headache within the past year, and recent headaches/bothered a lot within the past 4 weeks. Follow-up surveys were completed on average 3 years after baseline (mean=2.7 years; range=11.4 months to 4.5 years). RESULTS The overall male and female prevalence of self-reported headache conditions at baseline were: provider-diagnosed migraine, 6.9% and 20.9%, respectively; recurrent severe headache, 9.4% and 22.3%, respectively; and bothered a lot by headaches, 3.4% and 10.4%, respectively. Combat deployers had significantly higher odds of any new-onset headache disorders than non-deployers (adjusted odds ratios=1.72 for men, 1.84 for women; 95% confidence intervals, 1.55-1.90 for men, 1.55-2.18 for women), while deployers without combat exposure did not. CONCLUSIONS Deployed personnel with reported combat exposure appear to represent a higher risk group for new-onset headache disorders. The identification of populations at higher risk of development of headache provides support for targeted interventions.