There may be an upside for migraine sufferers. New research indicates that women with a history of the blinding headaches may be as much as 30 percent less likely to develop breast cancer than their headache-free friends. One possible glitch: the data doesn't rule out that nonsteroidal anti-inflammatory drugs (NSAID) such as ibuprofin – and not the migraines – deserve the credit.

"It may be the treatments used for migraines that are responsible for this risk reduction rather than the migraine itself," says study co-author Christopher Li, a cancer epidemiologist at Fred Hutchinson Cancer Research Center in Seattle. "We are interpreting the results with caution."

If painkillers are ruled out, he speculates that lower levels of the hormone estrogen may be behind both migraines and reduced cancer rates. His study notes that migraines are more common during menstruation (when there's a drop in estrogen) than at other times of the month and during pregnancy (when estrogen levels are high).  Breast cancer has been linked to greater estrogen levels throughout a woman's lifetime.

"I honestly am not surprised that this sort of association may exist," says neurologist Andrew Charles, who directs the headache research program at the University of California, Los Angeles and was not involved in the research. But he points out that the relationship between migraines and hormones is complicated and that genes might be the underlying link between migraines and tumors. "I think that there are other possibilities," he says.

Li says this is the first study to explore the possible relationship between migraines and breast cancer. But he notes that NSAIDS taken by migraine patients may account for the lower cancer risk as previous studies have shown.

It's also possible that women with migraines see their doctors more often and therefore end up in better health overall. But Li points out that women with more frequent visits would probably have more mammograms, which is associated with higher rates of breast cancer diagnosis. "It would be hard for me to think that that would account for a large portion of what we're seeing," he says.

Li says he and colleagues at the Fred Hutchinson Cancer Research Center and the University of Washington found the correlation between migraines and breast cancer during a survey of 2,000 post-menopausal women with breast cancer and 1,500 post-menopausal women with no history of breast cancer. Their findings, published today in the journal Cancer Epidemiology, Biomarkers & Prevention: Women who said they had been diagnosed with migraines at least once in their lives were 30 percent less likely to have developed invasive breast cancer. The survey did not ask women about what specific drugs they used to treat their migraines.

Li told that he hopes further research will help scientists to better understand the potential link between estrogen and breast cancer and to develop ways to reduce the disease. But first he'll have to rule out that it wasn't just the pills.