Potentials and pitfalls in analytical headache epidemiological studies--lessons to be learned from the Head-HUNT study.

The number of epidemiological headache studies is rapidly increasing, and has accentuated the need to improve the quality of the way studies are performed and how results are interpreted. The aims of this review were to summarize the main findings from the Head-HUNT study, to describe strengths and limitations of the Head-HUNT approach and to discuss the significance of some of our findings. Head-HUNT included a large sample size of 51 383 participants that gave the opportunity to make analyses also of relatively rare conditions. The wide range of health-related information made it possible to adjust for many potential confounding variables. Blood samples for future genetic headache studies are available for a non-selected large group of individuals. The data show that among several factors that have been evaluated, age and gender were the two most clearly related to migraine, whereas analgesic overuse and the presence of some comorbid conditions were most strongly associated with the prevalence of chronic headache. Interesting relationships to blood pressure and thyroid-stimulating hormone levels were also found. Methodological problems in headache epidemiological studies are discussed and, in particular, problems with causal inferences. Despite the limitations of the head-HUNT study, we believe that the results so far have provided clues to causes and preventive factors of headache that should be explored in other populations and in prospective studies.