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Do migraines protect against breast cancer?

by Ed Yong | Analysis

17 November 2008

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MigraineMigraines are very severe headaches that affect up to a quarter of people at some point in their lives. They can be very debilitating. Typical attacks can last for several hours and are often accompanied by nausea and sensitivity to both bright lights and loud noises.

Last week, a widely reported study suggested that there is an upside to these symptoms – a reduced risk of breast cancer. But is the study a ray of hope or a false alarm?

The research in question is the first of its kind – the only study to date to look at the rates of breast cancer in migraine sufferers compared to other women. A team of US researchers compared about 1,900 women with breast cancer to about 1,500 women without it and asked them if they had a history of migraines.

The results, published in Cancer Epidemiology Biomarkers and Prevention, showed that women who suffered from migraines had about a third lower risk of breast cancer compared to those who have never experienced them.

So does this mean that migraines protect against breast cancer? Not quite. The results point to an association between the two, but as always with studies like this, that doesn’t mean that one directly leads to the other.

The alternative is that something else lies behind both the presence of migraines and the lower risk of breast cancer, and that migraines are just acting as a ‘proxy’ for this other factor.

Fortunately, we (and the authors) have a pretty good idea what that something else might be – the hormone oestrogen.

Low levels of oestrogen are linked to a lower risk of breast cancer and there is some evidence that they also increase the frequency of migraines. For example, migraines tend to be more frequent during the point in the menstrual cycle when oestrogen levels are lowest, but less frequent during pregnancy, when oestrogen levels shoot up.

So if this link is real, it’s likely that both migraines and a lower breast cancer risk are both reflections of lower levels of oestrogen. Which makes this a slightly odd study. The authors suggest that looking at the link between migraines and breast cancer could improve our understanding of how hormones affect the risk of this cancer. But if migraines are just a proxy for hormone levels, why not study the hormones directly?

There is also another potential explanation for the results. Migraine sufferers often take painkillers for their painful headaches, including a group of drugs called non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and aspirin.

Some studies have suggested that these drugs could also reduce the risk of breast cancer so the association between migraines and breast cancer could just be a reflection of the painkillers that migraineurs take. Unfortunately, we can’t confirm or deny that theory because the researchers didn’t ask the people in the study if they took these drugs.

For the moment, this research doesn’t really have any major implications for women who suffer from migraines. While the results do suggest that they have a lower risk of breast cancer, they’re certainly not completely protected. There are other ways of actively reducing the risk of breast cancer, like cutting down on alcohol, keeping a healthy bodyweight and keeping physically active.

And certainly migraineurs should still be breast aware and go for screening when invited, to give themselves the best chance of spotting breast cancer early, when treatment’s most likely to succeed – whatever the headlines may imply.