Headaches are a common human affliction that affect people all over the world. They can be debilitating and result in loss of function in some people. But there are several different types of headaches and the causes are often not well understood. In addition, the methodology used to study headache prevalence has varied considerably in the past, which makes it challenging to estimate the global incidence of headache episodes.
In recent research, scientists from the Norwegian University of Science and Technology (NTNU) reviewed 357 publications, published between 1961 and the end of 2020, in an effort to estimate the global prevalence of headaches. The majority of publications considered in the review reported on headache incidence in adults between 20 and 65, but some also included adolescents and children down to the age of five, as well as elderly people over the age of 65.
Lars Jacob Stovner, professor of neurology at NTNU, and colleagues, quantified the differences in methods between the studies they reviewed. For example, while most studies reported headache prevalence in participants during the past year, some considered headache occurrence across the whole lifetime. And yet others reported headache prevalence over much shorter time periods, even within the previous day only. The researchers modelled these differences in methods and assessed how they may have impacted estimates in headache prevalence.
Based on the 357 publications reviewed, the authors estimate that 52 percent of the global population experience a headache disorder within a given year, with 14 percent reporting a migraine, 26 percent reporting a tension-type headache and 4.6 percent reporting a headache for 15 or more days per month. From the 12 studies that reported whether participants had experienced a headache the previous day, the authors estimate that 15.8 percent of the world’s population have a headache on any given day, and almost half of those individuals (7 percent) report having a migraine.
“We found that the prevalence of headache disorders remains high worldwide and the burden of different types may impact many,” said study lead author Lars Jacob Stovner. “We should endeavor to reduce this burden through prevention and better treatment. To measure the effect of such efforts, we must be able to monitor prevalence and burden in societies. Our study helps us understand how to improve our methods.”
Further findings from the study, published today in The Journal of Headache and Pain, include the fact that all types of headaches were more common in females than males, most markedly for migraines (17 percent in females compared to 8.6 percent in males) and headaches that lasted for 15 or more days per month (6 percent in females compared to 2.9 percent in males).
When trying to interpret the effects that study methods had on headache estimates, the researchers calculated the amount of variation in migraine prevalence that was explained by various methodological factors, such as screening questions, sample size, publication year, and how diagnostic criteria were applied. These variables explained a total of 29.9 percent of the differences in migraine estimates and even less for other headache disorders. This suggests that there may be other methodological factors accounting for the greater variations across the studies.
Interestingly, the researchers found that year of publication accounted for six percent of the variation in headache estimates, with more recent studies being associated with higher estimates of headache prevalence. The publication year did not account for the variation in other headache types, leading the authors to propose that this might reflect a real increase in migraine occurrence over the past three to four decades. Alternatively, this finding could indicate that the diagnosis of migraines has improved during this time.
The study authors acknowledge that the majority of studies they reviewed came from high-income countries with good healthcare systems so the findings may not reflect the situation in all countries. Further investigation into the situation in middle and low-income countries would help present a more accurate global estimate. However, the authors did use a wide range of studies for their review, thus obtaining data from as many countries as possible. These studies sampled participants within and outside of clinical settings, including employees of a company, university students and hospital staff, amongst others.
“Compared to our previous report and global estimates, the data does suggest that headache and migraine rates may be increasing,” said Lars Jacob Stovner. “However, given that we could explain only 30 percent or less of the variation in headache estimates with the measures we looked at, it would be premature to conclude headaches are definitively increasing. What is clear is that overall, headache disorders are highly prevalent worldwide and can be a high burden. It may also be of interest in future to analyze the different causes of headaches that varied across groups to target prevention and treatment more effectively.”
The researchers conclude that this study provides a baseline for how to estimate headache rates across the world and future research could build on this to improve methods for measuring the success of interventions and treatment.