For women there may be one good thing about having migraines: a reduced risk of breast cancer.

In a study of more than 9,000 people, Dr. Christopher I. Li of Fred Hutchinson Cancer Research Center in Seattle and his colleagues found that those with a history of migraines were 26 percent less likely to develop breast cancer. The findings back up an earlier study, also by Li and his team, which included about 2,000 women and found a 33 percent lower breast cancer risk among women with migraines.

Low estrogen levels appear to increase the severity and frequency of migraines in women, the researchers note in their report, while increased levels of the hormone are known to boost breast cancer risk, so it's "biologically plausible" that migraine sufferers would be less prone to breast cancer.

In the current study, Li and his team compared 4,568 women with breast cancer, ranging in age from 34 to 64, to 4,678 healthy controls. They accounted for the effects of migraine triggers such as alcohol, smoking or hormone use, which hadn't been done in the previous study.

The researchers found a 26 percent lower risk of breast cancer in the women with migraines, which didn't change when they took migraine triggers or whether or not a woman was menopausal into account. Similarly, use of prescription drugs for migraine did not change the risk.

Migraine patients' greater use of non-steroidal anti-inflammatory drugs (NSAIDS), painkillers including ibuprofen and naproxen, could explain some, but probably not all, of their lower breast cancer risk, Li and his colleagues say. (A recent analysis of several studies linked NSAID use to 12 percent lower breast cancer risk.)

"Further work is needed to resolve what accounts for this relationship," the authors conclude.