We’ve all heard it: having migraine with aura increases your risk of stroke. We know it. Our doctors know it. Hopefully, our loved ones know it and are watching for it. But, what does that increase really mean, by itself and in combination with other risk factors, such as taking certain medications?
A long-term Women’s Health Study presented in 2013, put the relative risk of stroke in female migraine patients with aura at 4.3 per 1,000 per year. This is the largest relative risk rate seen so far in studies (several other meta-analyses have shown the relative risk for female migraineurs under age 45 to be closer to 3.65), and indicates that migraine with aura is “a strong contributor to stroke risk,” more so, even, than smoking (2.9 per 1,000/year), high cholesterol (1.2 per 1,000/year), obesity (2.3 per 1,000/year), and family history of heart attack (2.9 per 1,000/year).
From these numbers, it appears clear that migraine with aura is a substantial risk factor for stroke. It’s important to note, however, that these numbers are dealing with relative risk and not absolute risk.
Relative risk is used to compare two groups of people. For instance, in the study above, 2.9 more smokers per 1,000 per year will experience a stroke than non-smokers. Absolute risk is the real odds of experiencing a stroke, in absolute terms.
A 2009 meta-analysis showed that having migraine with aura doubles the risk factor of stroke in men and triples the risk in women. It also showed additional increases in risk for female migraineurs with aura under the age of 45 who smoked and took combined oral contraceptives (the pills with estrogen), but that still doesn’t tell us much. A triple-fold increase sounds scary, but it’s really only relevant if we know the true absolute risk of stroke.
According to a review study published in 1997, the absolute risk for stroke in female migraineurs with aura who are under the age of 35 and don’t take the pill is roughly .008%, or 8 in 100,000 per year. Introducing estrogen birth control pills raises the instance of risk to 28 in 100,000 per year. (For comparison’s sake, women of the same age who took the pill but did not have migraine had an absolute risk of 5 in 100,000 per year.)
These numbers suggest that despite the real increase in relative risk for migraineurs with aura, the actual absolute risk for having a stroke is still very low. Since our doctors are here to educate us and inform us about risks and options but not to make our decisions for us, that means we may still have some decisions to make on our own.
My obgyn, for instance, told me shortly after I started seeing her that she was “uncomfortable” prescribing me birth control pills with estrogen because of my aura. She said she didn’t want to compound my risk of stroke by adding two risk factors together. While I appreciated her honesty and the information, I ultimately made my own decision based on how comfortable I was with the overall risk. We all should have enough information to do the same. Our health choices, after all, are ultimately ours to make.