A new study finds migraine headaches that are accompanied by auras double the risk for having a stroke.

An international team of researchers analyzed nine migraine studies for the results published in the British Medical Journal. They found that migraine with aura is associated with a twofold increased risk of ischemic stroke. This risk is further increased by being female under the age of 45, smoking, and using estrogen containing contraceptive, like birth control pills.

One of the researchers involved with the study says the absolute risk of stroke for most migraine patients is low, so a doubling of risk is not cause for panic. She adds that the risk shouldn’t be ignored and that doctors should closely follow patients who have these headaches to assess other cardiovascular risk factors.

Migraine headaches affect up to 20 percent of the population, with women being affected up to four times as often as men. About one-third of sufferers have auras with their headaches. They are described as temporary visual or sensory disturbances before or during a headache.

Among some of the alternative treatments believed to help treat migraines are acupuncture, chiropractic methods and biofeedback, according to The National Migraine Association.