Researchers baffled with increase in migraine rates

Migraine rates in a comprehensive Norwegian health study have climbed by 1% in a decade -- that may not sound like much, but in the Norwegian context, it means 45,000 more migraine sufferers -- and if the trend were to hold for the European Union, that would be an additional 5 million more people plagued by migraines. Researchers at the Norwegian University of Science and Technology (NTNU) are baffled by the cause of this trend.

The findings, in which researchers compared data from a survey conducted in the mid-1990s to data collected in 2006-2008, shows that people aged 20-50 years are more prone to migraines now than in the mid 1990s.

The numbers are derived from the second and third phases of the Nord-Trøndelag Health Study, called HUNT 2 and 3 after their Norwegian acronyms, which represents one of the largest comprehensive health studies in the world. HUNT 2 involved the collection of a health history during 1995-1997 from 74,000 people, with the collection of blood samples from 65,000 people. The follow-up in 2006-2008, called HUNT 3, involved 48,289 people, many of whom were represented in the earlier study.

The findings showed that while 12 per cent of the population met the medical criteria for having migraine headaches in the HUNT 2 survey, 13 per cent of the HUNT 3 respondents 11 years later  met the medical criteria for having migraines.

While that 1 per cent increase "may not sound dramatic, in the context of the population as a whole, that represents an increase of roughly 45 000 Norwegians," says Professor Knut Hagen, one of the NTNU researchers working with the data.  "Those are real numbers and give some cause for concern. The increase has also occurred over a relatively short period of time."

The increase is most marked in the age group 20-50 years, but is also found in older age groups. Hagen does not have data for people younger than 20.

The most puzzling aspect of the finding is that it has no obvious scientific explanation, Hagen says. Diagnostic criteria were the same in the 1990s as they are today, and the level of self-reported migraine did not increase. The number of migraines caused by medicines has also not increased between the HUNT 2 and HUNT 3 databases, he said.

"This last finding is really good news because the use of pain relievers has risen sharply since these drugs have been available for sale in stores without a prescription," says Hagen.

A more likely explanation for the increase in migraines is a change in the external environment, Hagen says.

"From experience we know that visual impacts, such as flickering screens, can trigger migraines. Measurements of the neurophysiological activity in the brain with EEG shows that migraine patients are more susceptible to light stimulation. It is tempting to believe that the increase in migraines is due to the increase in these kinds of stimuli during the 11 years between the two HUNT surveys," Hagen says. "But this is speculation that we have no scientific evidence for."

But Hagen was clear that one possible candidate - radiation from mobile devices - was not a cause of the increase, based on the results of a previous NTNU study, which found no evidence that radiation from mobile phones contributed to an increase in headaches.

http://cep.sagepub.com/content/31/5/585