The study is the first to look at the relationship between breast cancer and migraines and its findings may point to new ways of reducing a woman's breast cancer risk, they said.
"We found that, overall, women who had a history of migraines had a 30 percent lower risk of breast cancer compared to women who did not have a history of such headaches," said Dr. Christopher Li of the Fred Hutchinson Cancer Research Center in Seattle, whose findings appear in the journal Cancer Epidemiology, Biomarkers and Prevention.
Li said the reduction in risk was for the most common types of breast cancers -- those driven by hormones, such as estrogen-receptor positive breast cancer, which is fueled by estrogen, and progesterone-receptor positive breast cancer, which is fueled by progesterone.
Hormones also play a role in migraines, a brutal type of headache often accompanied by nausea, vomiting and heightened sensitivity to light and sound. Women are two to three times more likely than men to get migraines.
While it is not exactly clear why women with a history of migraines had a lower risk for breast cancer, Li and colleagues suspect hormones are playing a role.
"Women who have higher levels of estrogen in their blood have higher levels of breast cancer," Li said in a telephone interview.
And he said migraines are often triggered by low levels of the hormone estrogen, such as when estrogen levels fall during a woman's menstrual cycle.
Women who get migraines "may have a chronically lower baseline estrogen. That difference could be what is protective against breast cancer," Li said.
For the study, Li and colleagues analyzed data from two studies of 3,412 post-menopausal women in the Seattle area, 1,938 of whom had been diagnosed with breast cancer and 1,474 of whom had no history of breast cancer. Women in the study provided information on their migraine history.
They found women who had reported a clinical diagnosis of migraine had a 30 percent reduced risk of developing hormonally sensitive breast cancers.
"Migraines are typically most severe among pre-menopausal women," Li said. "This study was all post-menopausal women."
He said that suggests the protective effect seen in women who get migraines may have a lasting effect at reducing breast cancer risk.
"While these results need to be interpreted with caution, they point to a possible new factor that may be related to breast-cancer risk," Li said in a statement.
Breast cancer is the leading cause of cancer death among women worldwide, with an estimated 465,000 deaths annually, according to the American Cancer Society.
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