In a puzzling twist, women who have a history of migraine headaches are far less likely to develop breast cancer than other women, researchers from the United States said recently.

The study is the first to look at the relationship between breast cancer and migraines.

'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 Dr Christopher Li of Fred Hutchinson Cancer Research Center in Seattle, whose findings appear in the journal Cancer Epidemiology, Biomarkers And Prevention.

Dr Li said the reduction in risk was for the most common types of breast cancers - those driven by hormones, such as oestrogen-receptor positive breast cancer, which is fuelled by oestrogen, and progesterone-receptor positive breast cancer, which is fuelled by progesterone.

Hormones also play a role in migraines and women are two to three times more likely than men to get such headaches. While it is not exactly clear why women with a history of migraines had a lower risk of breast cancer, Dr Li and his colleagues suspect hormones are playing a role.

'Women who have higher levels of oestrogen in their blood have higher risk of breast cancer,' he said. He added that migraines are often triggered by low levels of the hormone oestrogen, such as when oestrogen levels fall during a woman's menstrual cycle.

Women who get migraines may have a chronically lower baseline oestrogen. That difference may have a preventive effect against breast cancer, said Dr Li.

He and his colleagues analysed data from two studies of 3,412 post-menopausal women - 1,938 of whom had been diagnosed with breast cancer and 1,474 of whom had no history of breast cancer.

They found women with a clinical diagnosis of migraine had a 30 per cent reduced risk of developing hormonally sensitive breast cancers.

'While these results need to be interpreted with caution, they point to a possible new factor that may be related to breast cancer risk," Dr Li said.

Reuters

This article was first published in Mind Your Body, The Straits Times on Nov 13, 2008.