WEDNESDAY, Feb. 17, 2016 (HealthDay News) -- Migraine sufferers may face an increased risk of stroke if they suffer from visual symptoms called auras or if they take the female hormone estrogen, a pair of new studies suggests.
People who have migraine headaches with auras may be 2.4 times more likely to have a stroke caused by a blood clot, compared to migraine patients who don't see auras, says one study scheduled for presentation Wednesday at the American Stroke Association's annual meeting, in Los Angeles.
And, women with more severe migraines who take hormone-replacement therapy may be 30 percent more likely to suffer a clot-based stroke than women not taking medication containing estrogen, according to a second paper to be presented at the meeting.
The two risk factors could combine to pose a dangerous mix for some women, said Dr. Elizabeth Loder, chief of the headache and pain division at Brigham and Women's Hospital in Boston.
"Women who have migraine with aura probably want to think more carefully about the potential risk of stroke associated with using estrogen," Loder said. "I would not go so far as to say they should never use it, but they should think more carefully about it."
Estrogen, a female hormone, is contained in birth control pills and hormone-replacement therapy.
It's important to note, however, that the new research only found associations between migraines with aura, estrogen therapy and stroke risk. It did not prove cause-and-effect.
The two studies focused on strokes caused by blood clots, which account for about 87 percent of all strokes in the United States, according to the American Stroke Association.
One study took a closer look at migraines with aura, which have been established by earlier research as a risk factor for stroke, the researchers said in background information.
About one in five migraine sufferers experiences visual symptoms before and during a headache, said study author Dr. Souvik Sen, a neurologist at the University of South Carolina School of Medicine. These symptoms can include flashes of light, blind spots, or seeing zigzag or squiggly lines.
In a 25-year ongoing study of nearly 13,000 adults in four U.S. communities, researchers identified 817 participants who had suffered a blood-clot stroke.
They found that migraine patients who experience aura symptoms seem more likely to suffer a blood-clot stroke than typical migraine sufferers. Specifically, people who have migraine with aura appear to be three times more likely to have a stroke caused by a clot that forms in the heart, dislodges and travels to the brain, the study authors said.
They're also seem twice as likely to have a stroke caused by a clot that develops in a clogged part of the blood vessel supplying blood to the brain.
Future research needs to look into blood flow patterns in the brains of migraine-with-aura patients, Sen said.
"The aura is an effect of migraine on the blood vessels of the brain," Sen said. "When they have the vision symptoms, it could be an effect of the migraine on the blood vessels of the brain."
The other study focused on another known risk factor for stroke -- medications containing estrogen.
"Estrogen, which is contained in hormone-replacement therapy and in certain kinds of combination birth control pills, increases the likelihood of blood clots," and thus increases stroke risk, Loder said.
Researchers analyzed data for more than 82,000 women 50 to 79 years old from the Women's Health Initiative, a study begun by the U.S. National Institutes of Health in the early 1990s. All reported having some degree of migraines, and about 45 percent were using hormone replacement.
At a follow-up visit three years later, women completed a questionnaire to determine if their migraines had gotten better or worse.
Women who experienced worsening migraines while taking hormone-replacement therapy appeared to be 30 percent more likely to have a clot-based stroke than migraine sufferers who either stopped taking or never took hormone-replacement therapy, researchers concluded.
Study lead author Dr. Haseeb Rahman, a neurology resident at Houston Methodist Hospital in Texas, said the findings suggest women on hormone replacement therapy should notify their doctor of any migraine symptoms.
"You should not simply ignore an increasingly bad migraine," said Rahman, who worked on the study with a research team from the Zeenat Qureshi Stroke Institute in Minneapolis. "You should also tell your doctor if you're getting migraines for the first time while on hormone replacement therapy."
However, Loder noted that the increased risk is "certainly higher than we would like it to be, but it's not terribly high," given that just 2,063 women experienced clot-based strokes out of more than 82,000 female migraine sufferers.
"Other risk factors like smoking and high blood pressure are much more important," Loder said. "It's important to put the risk into context."
Migraine sufferers or women taking estrogen should address more important risk factors, Loder said, by quitting smoking, controlling their blood pressure, treating their diabetes or lowering their cholesterol.
Data and conclusions presented at meetings should be considered preliminary until published in a peer-reviewed medical journal.
For more about migraine and stroke, visit the Stroke Association (UK).