Somewhere, at some point, you may have heard there was some sort of link between migraine and stroke – more specifically, that having migraines meant you were at a heightened risk of a brain infarction. Most likely, you heard this from a major television or print media outlet that gave you a few cursory tidbits designed for maximal anxiety arousal and attention grabbing, and then moved on to the next story about Justin Bieber’s new brand of toothpaste.
And you’d be right to be concerned by this piece of news. Strokes are serious business. But what’s the actual connection here? And, if there is one, should you be doing something about it? Is there a ticking time bomb in your head, and is it only a matter of time till it goes off?!!
Multiple studies have been done to investigate a potential link between migraine and stroke, using various designs and analytical techniques. As you might expect, the results vary to some degree. This is what happens when you try to discern cause and effect relationships from epidemiological data. It’s the wrong tool for the job. Nonetheless, in this case it’s the best we’ve got.
Sometimes, when you have a mess of epidemiological data to untangle, it can be helpful to pool the results across many studies into one big analysis (a “meta-analysis”) and see what turns up. Fortunately, this sort of thing has been done for us.
So what was found after compiling all the data together?
On the surface at least, it appears that, based on this analysis, there is at least some connection between migraine and stroke. The risk of stroke in folks with a history of migraine was found to be, on average, 1.73 times greater than the risk in those without them. That statistic is a little misleading, however.
If we further segregate migraineurs into those with aura and those without, however, we find that the heightened stroke risk only holds true for those who have migraines with aura. There is no statistically significant difference in stroke risk between those with a history of migraines without aura and the normal control population.
When we do look at just those who experience migraine with aura, we find that their risk of stroke is roughly double that of migraine-free controls. So, according to this data, if you have a history of migraine with aura, your risk of a stroke is twice that of a person who doesn’t have them (but is otherwise just like you).
Take Home Message:
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Adding some perspective
At first blush, this does sound a bit concerning. Having migraines with aura doubles your risk of a stroke.
But let’s put this in perspective.
To start, first consider the risk of stroke among the general population, particularly in those age groups where migraines are most common. According to the statistics from the AHA , the annual risk of stroke in those aged 45-54 is around 1 per 1,000. Few published statistics on annual risk exist for those under 45, as the rates are even lower.
So, if the risk of stroke for a typical American aged 45-54 is 1 in 1,000 per year, or 0.1%, what’s the annual stroke risk of someone with migraine with aura? 0.2%, or 1 in 500.
So, yes, the risk goes up, but even so still remains very low. This is the difference between relative risk (double in this case) and absolute risk (1 in 500). Usually, media outlets will only report the relative risk numbers, since they almost always seem more dramatic (“migraines double your stroke risk, details at 11!”).
Take Home Message:
WHEN WE CONSIDER THE ABSOLUTE RISK OF STROKE IN THOSE WHO HAVE MIGRAINE WITH AURA, IT’S STILL VERY LOW
An alternative explanation
Now, at this point I think it’s worth mentioning that all of this data could be entirely wrong. In fact, I personally think that it’s more likely than not that this data is wrong.
Why do I say this?
As you now know, the evidence shows a connection between migraine and stroke only for those who also experience auras with their migraines. And what is an aura? It’s a transient neurological disturbance, typically lasting anywhere from 20-60 minutes, produced by a wave of “spreading depression” in a particular part of the brain. Auras are most commonly visual in nature, but essentially any type of neurological disturbance can occur.
But migraine auras aren’t the only thing that cause transient neurological disturbances. So do transient ischemic attacks, or TIAs. In the case of a TIA, the disturbance in function isn’t caused by spreading depression, but rather the interruption of blood flow to a particular part of the brain. So how can we tell for sure if a someone’s transient neurological disturbance was from an aura or a TIA?
There is no definitive way to answer that question, no diagnostic tool to resolve the issue with absolute certainty. There are factors that can tip the probability scales towards one diagnosis or the other, for sure, but in the end that’s all the diagnosis is based on…probability. Ultimately, determining whether someone has experienced an aura or a TIA is just an educated guess. And, we know without a doubt that in some cases that guess will be wrong.
Why is this important?
Because if your transient disturbance in neurological function was from a TIA, your risk of stroke in the following year is a whopping 20%.
All of these studies on migraine with aura and stroke assume that the migraine study population is untainted – that every single person has been correctly diagnosed. Yet, the odds of this being true are virtually nil. So how many people in our study population would need to be misdiagnosed as migraine with aura instead of TIA to render this migraine and stroke association completely null and void?
Let’s crunch the numbers.
In our earlier meta-analysis, having a migraine with aura increased your risk of stroke by a factor of 2 — from 1 in 1000 to 2 in 1000 (or 1 in 500). The difference in stroke risk between the two groups, then, is 1 in 1,000. Now, if we know that 20% of people, or 1 out of every 5, with a TIA will go on to have a stroke in the ensuing year, then we’d only need 5 misdiagnosed people in a study population of 1,000 for one of those people to have a stroke. And if one of those folks has a stroke, then that would account for the increased risk in this population entirely. In other words, simply misdiagnosing 1 out of every 200 people with a migraine with aura instead of TIA is all it takes to nullify the stroke and migraine connection altogether.
Is misdiagnosing 1 out of every 200 with migraine with aura instead of TIA plausible? Indeed.
Not just plausible, but probable. In clinical practice, this isn’t at all uncommon. In fact, given our current diagnostic capabilities, it’s unavoidable. The truth is, getting 199 out of every 200 cases right would be a pretty darn good batting average.
Take Home Message:
For argument’s sake, let’s just assume that the worst case scenario is true: that having a history of migraines with aura doubles your stroke risk. Is there anything you should be doing?
For starters, don’t smoke cigarettes, and avoid take oral contraceptives if at all possible. We know that each of these factors independently raises stroke risk even further in those migraineurs with aura.
Beyond that, what else can you do to lower your risk?
As it turns out, there are populations of humans in whom stroke is either non-existent or a medical oddity – indigenous societies still largely leading a hunter-gather existence. Societies like the Kitavans in Papau New Guinea, where, after systematic examination by Stefan Lindeberg and colleagues, not a single case of stroke could be found amongst all its inhabitants.
It stands to reason, then, that if we emulate these folks, we can afford ourselves the same protection against stroke. So what is it in the way they eat and live that’s protecting them from stroke?
Is it a diet that’s low in saturated fat?
Hardly. The Kitavan diet, for example, is loaded with saturated fat, much of it in the form of their beloved coconut.
Is it their avoidance of animal products or red meat?
Nope. No non-meat eating native society has ever been found. In fact, in virtually all of them, including those that are stroke-free, animal flesh and organs are their preferred food source, as they are loaded with calories and nutrients and require the least amount of effort to secure – important considerations if you’re faced with the task of securing your own food every day.
Is it their rigid adherence to a monthly regimen of juice fasts?
Sorry, couldn’t resist.
Given that these societies exist in different parts of the world with a wide variety of dietary patterns, it is likely that their protection from stroke has much less to do with what they do eat than it does with what they don’t eat.
So what don’t they eat?
- Processed (industrial) foods
- Vegetable and seed oils (again, things made in a factory)
- Refined sugar and high fructose corn syrup
- Wheat and other gluten grain flours
To emulate those societies free of stroke, then, our top priority should be to avoid eating these things as well. As luck would have it, adopting this way of eating also happens to be the single best thing you can do to prevent migraines.
Take Home Message:
Isn’t that a happy coincidence?
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