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

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-Trøndelag 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.