The study’s unusually long follow-up period is a strength, says neurologist Jason Rosenberg, M.D., director of the Johns Hopkins Headache Center, in Baltimore.
“It’s been well-known that migraine and depression occur together much more commonly than can be explained by chance,” says Rosenberg, who was not involved in the study. “This study gets us one step closer to establishing the link that migraine seems to precede depression.”
On the other hand, Rosenberg says, the fact that all of the study participants were over the age of 45 does limit the findings somewhat. “Most women develop migraine when they are well under 40,” he says. “An older population could skew the results one way or the other.”
There is no clear explanation for the migraine-depression link. Although frequent migraines could usher in depression by reducing a person’s quality of life, underlying—and as yet unknown—biological factors may play a role as well. In the future, Kurth says, scientists should try to identify brain chemicals that may contribute to both conditions.
“Are there common biomarkers in the neurotransmitters of the brain?” Kurth says. “I hope our research will stimulate targeted research that will look for mechanisms and figure out exactly what is going on.”
Determining whether the frequency and severity of headaches influence the risk of depression will be another important piece of the puzzle, Rosenberg says.
Previous research suggests that depression risk rises along with migraine severity, Kurth says. He and his colleagues have not yet addressed that point, but they expect to in the future.