Women who have higher levels of estrogen in their blood have higher levels of breast cancer, research indicates.Women who have higher levels of estrogen in their blood have higher levels of breast cancer, research indicates.

Women who suffer from migraines also seem to gain a much lower risk of breast cancer, according to a study released Thursday.

The study is the first of its kind to look at the hormonal relationship between breast cancer and the severe throbbing headaches that can cause vomiting, nausea and sensitivity to light, sound and smells.

"We found that, overall, women who had a history of migraines had a 30 per cent lower risk of breast cancer compared to women who did not have a history of such headaches," said study author Dr. Christopher Li, a breast cancer epidemiologist at the Fred Hutchinson Cancer Research Center in Seattle.

Writing in the November issue of Cancer Epidemiology, Biomarkers and Prevention, Li and his colleagues cautioned that since this is the first study to address the link between migraine history and breast cancer risk, more research is needed to confirm the finding.

The preliminary findings have no implications in terms of changing recommendations for getting mammogram screenings.

"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. "This gives us a new avenue to explore the biology behind risk reduction."

Exploring hormone links

Migraine history appeared to reduce the risk of the more common types of breast cancer that are driven by hormones, namely estrogen receptor-positive and progesterone receptor-positive cancers.

These types of tumours have estrogen and/or progesterone receptors on the surface of their cells, which makes them more responsive to hormone-blocking drugs.

"Women who have higher levels of estrogen in their blood have higher levels of breast cancer," Li said in a telephone interview.

Migraines are often triggered by low levels of the hormone estrogen. Women prone to migraines "may have a chronically lower baseline estrogen. That difference could be what is protective against breast cancer," Li said.

Pregnancy, a high estrogen state, is also associated with a significant decrease in migraines. On the other hand, women who take oral contraceptives tend to suffer more migraines during their hormone-free week, Li noted.

In the case-control study, the researchers compared 1,938 postmenopausal women who had been diagnosed with breast cancer and 1,474 who had no history of the disease.

Participants were asked to report whether they had been diagnosed with migraines.

Specifically, migraines were associated with a 0.65-fold reduced risk of estrogen receptor-positive/progesterone receptor-positive ductal breast cancers, the researchers said.

The reductions in risk were seen among all migraine sufferers, regardless of whether they took prescription medications for the headaches.

An estimated 22,670 Canadians will be diagnosed with breast cancer this year, and 5,400 will die of it, according to Canadian Cancer Statistics 2008.

About 7.9 per cent of people over 12, or 1,956,000 Canadians, have been diagnosed with migraines, according to Statistics Canada's 1998-99 national population health survey.

With files from Reuters