Headache and insomnia in population-based epidemiological studies.

Background: Several epidemiological studies on the association between primary headaches and insomnia have been published in recent years. Both disorders are frequent, and our purpose was to review results from population-based studies exploring this association. Methods: We performed a literature search in PubMed for "insomnia" (or sleep disturbance) and "headache" (or migraine) linked with "epidemiology." Two hundred and eight records were identified. Three longitudinal and 10 cross-sectional studies met our inclusion criteria: population-based design with at least 200 participants including a numerical estimate of the association between headache and insomnia. Results and conclusions: In nearly all studies, primary headaches, including migraine and tension-type headache, were significantly related to insomnia symptoms with OR estimates ranging from 1.4 to 1.7. The odds were even greater, from 2.0 to 2.6, for frequent, comorbid or severe headache. Recent large longitudinal studies from Norway found a bidirectional, possibly causal, association between headache and insomnia. However, not all studies used standardized diagnostic criteria for either headache or insomnia. Further research should use well defined and validated diagnostic criteria both for insomnia and headache types in order to improve the comparability between studies, investigate causality and clarify the relevance of the findings for clinical practice.