Researchers have found over the years that any number of factors--weather changes, chocolate, sleeping patterns, alcohol, stress, odors and so on--can trigger migraine headaches in different people. Now a new study has confirmed a strong correlation between certain types of migraines and the onset of menstruation. Reporting in today's issue of Neurology, Stephen Silberstein and his colleagues at Thomas Jefferson University Hospital in Philadelphia say that women are twice as likely to experience migraine without aura--the type most often associated with menstruation--during the first two days of their cycle. "If women have a better idea when they'll get a migraine during their cycle, they have a better chance to prevent or treat it," Silberstein says. "That's important news--especially when you consider that 70 percent of all migraine suffers are women."

For roughly three months, the scientists tracked 81 women diagnosed with migraine. The women kept detailed diaries, chronicling not only when their headaches occurred but also specific features of the pain, other symptoms such as nausea and whether the episode was sufficiently disabling as to prevent them from going to work or getting much done. The study, funded by Astra Zeneca Pharmaceuticals, found that 28 percent of the migraines without aura experienced by the subjects took place within the four days surrounding the start of menstruation. During this period, tension headaches, too, were more likely. At the same time, there was no increase in the type of headache known as migraine with aura, nor was there any indication that the migraines associated with menstruation were more painful. "Menstruation was a powerful trigger for migraine," Silberstein notes, "but the headache wasn't any different than those triggered by alcohol or chocolate." Other work has suggested that it is the drop in estrogen during menstruation that actually provokes the migraine attack.