The long-term effect of insomnia on primary headaches: a prospective population-based cohort study (HUNT-2 and HUNT-3).

(Headache 2011;51:570-580) Objective.— Few prospective studies have evaluated the relationship between insomnia and headache. We aimed to analyze the influence of insomnia at baseline on the risk for headache 11 years later. Methods.— This longitudinal cohort study included subjects who participated in 2 consecutive surveys of the Nord-Trondelag Health Study (HUNT-2 and HUNT-3). Among the invited individuals aged 20 years or more in HUNT-2 (n = 92,566) and HUNT-3 (n = 94,194), a total of 26,197 completed the headache section of both surveys. A proxy insomnia diagnosis based on DSM-IV at baseline and ICDH-2-based headache diagnoses at follow-up were derived from questionnaires. Headache-free individuals in HUNT-2 (n = 15,268) were selected for analysis. The relative risks (RRs) for headache in insomniacs were calculated with logistic regression. Results.— The presence of baseline insomnia was associated with a 40% increased risk for headache in HUNT-3 (RR = 1.4, 95% CI = 1.2-1.7). Similar results were found for tension-type headache (TTH), migraine, and non-classified headache. Subjects with insomnia-related working disability had a 60% increased headache risk (RR = 1.6, 95% CI = 1.3-2.1). The RR was larger for migraine (RR = 2.0, 95% CI = 1.3-3.1) than for TTH (RR = 1.5, 95% CI = 1.1-2.1). Insomnia at baseline was related to headache frequency at follow-up for both migraine (P trend = 0.02) and TTH (P trend < 0.001). Conclusion.— In headache-free subjects, insomnia was associated with an increased risk of headache 11 years later. The association was particularly strong for chronic headache.