Welcome back to our weekly diabetes advice column, written by longtime type 1 and diabetes author Wil Dubois.

This week, Wil's looking at whether low blood sugars can lead to heart issues and strokes. You may be surprised, because it's not always as clear as you might think.

{Need help navigating life with diabetes? Email us at AskDMine@diabetesmine.com}


James, type 2 from Montana, writes: After reading last week’s Ask D’Mine  I got to wondering: Can low blood sugars cause a stroke?

Wil@Ask D’Mine answers: Heart attacks, you bet. Brain damage, sure. But strokes? Nope! Well… probably not. OK… kinda sorta, in a way… maybe… 

Here’s the problem. While there’s yet to be any significant body of evidence that shows hypos trigger strokes, there is some evidence that suggests that folks who have a lot of lows might have worse strokes, when they do have them, than do people who don’t have a lot of lows. 

Where did that come from?

Well, according to research done by Kunjan Dave, John Tamariz, Kushal Desai, Frank Brand, Annie Liu, Isabel Saul, Sanjoy Bhattacharya, and Antonello Pileggi (that’s quite a large team!), and published in the journal Stroke—one of the peer-reviewed research journals of the American Heart Association—recurrent hypoglycemia “exacerbated” stroke damage.

At least in diabetic rats.

OK, OK. Don’t stop reading. As my boss at the clinic where I worked for half my adult life famously said, “Rats are people, too.” And this is a serious enough issue to consider, even if the evidence is only animal. As the authors point out, strokes, along with heart disease, kill more than 65% of PWDs. And while the effect of high blood sugar is understood (and I’ll talk about that in a few minutes) no one had ever looked at the effect of the unintended consequence of intensive therapy on strokes and stroke outcomes. What unintended consequence would that be? 

Low blood sugar.

And sure enough, when the researchers dug into it, among diabetic rats with recurrent hypoglycemia, the poor little critters got messed up much worse by the strokes than did diabetic rats with no lows.

Now, for you deep thinkers who wonder how on earth the researchers were able to give the rats diabetes, the beta cell toxin streptozotochin was used. For those of you wondering how on earth you check a rat’s blood sugar, the answer is: Tail pricking. And a Bayer Ascensia meter. And where’d they get their insulin shots? They didn’t. For basic diabetes control, all the rats were given subcutaneous insulin pellets. OK, and the hypos? The rats chosen for hypos were given two lows a day, for five days, from Novolog injections in their femoral arteries, on top of their pellet treatments. To trigger lows, the rats got 0.25 units of insulin per kilogram of body weight. For a 200-pound human that would translate into about 22 units. How low did it drop the rats? Actually, not as low as you’d think, only to 55-65 mg/dL, where they were held for a half an hour before being injected with sugar to bring them back up.

Actually, that’s the aspect of this study that scared me the most. That kind of low is hardly desperate. In fact, both the level and the length of time are hardly uncommon for most of us who use insulin.

Moving on, you’re probably next wondering how on earth they gave the rats strokes. I guess at this point I’d better point out that there are two types of strokes. The first type is called ischemic, and this is caused by a blockage of the blood supply to the brain by a blood clot. The second type is called hemorrhagic, and is caused by the bursting of a blood vessel in the brain. Both types can cause permanent damage to your grey matter. Or kill you.

But the ischemic strokes are the more common kind, and it was a relatively simple matter for the researchers to simulate them in the rats by blocking the blood flow to their little rat brains. They did this by choking off their carotid arties. Each was given an eight minute stroke.

Hey, don’t shoot the messenger. Apparently, despite all this Inquisition-like torture, the rats were cared for under the Guide for the Care and Use of Laboratory Animals published by the National Institutes of Health, which specifies the “highest scientific, humane, and ethical principles.”

But back to the study, just how much worse was the stroke damage on the hypo rats? Are you sitting down? There was a 70% increase in neuronal death compared to the control group. That’s huge.

So what’s the mechanism here? How do recurrent lows lead to larger numbers of dead brain cells in the setting of a stroke? Well according to the researchers, recurrent hypoglycemia increases free radical release from mitochondria, which in turn “increased ischemic damage.” 


OK. It’s not as bad as it sounds. Starting at the back, “increased ischemic damage,” is just a fancy way of saying more brain cells were killed in the stroke. And mitochondria? Crudely put, that’s a cell’s lung. Well, more of a lung and a digestive system combined. Mitochondria handle respiration and energy production. And free radicals? They aren’t loopy protestors with peace signs, pot pipes, and protest signs. They are highly reactive uncharged molecules, which trigger oxidative stress, which in turn is the smoking gun in most types of tissue damage complications of uncontrolled diabetes.

So we don’t want no free radicals. At least in our bodies. 

Unlike heart attacks and brain damage, where a single bad low can either trigger a heart attack or cause brain damage, the connection between strokes and lows is more complex. The lows set up an environment in which, if a stoke happens, it’s super-sized.

So you sure as shit want to avoid a stroke if you are having a lot of lows. But, again, it doesn’t seem that the lows themselves trigger strokes. There’s no evidence for that yet. Of course, bear in mind only a few years ago we didn’t understand that lows triggered heart attacks, either. So who knows? But what we do know is that strokes can be triggered by high blood sugar.

Yeah. High blood sugars absolutely increase stroke risk. Oh, and one other thing to keep in mind is that high blood sugar, in addition to being a trigger for a stroke in the first place, has a role to play in how that stroke plays out. High blood sugar reduces “clinical outcomes” post-stroke, a fancy white-coat way of saying you’re more likely to croak following a stroke if your blood sugars have been running high. So it looks like both high and low blood sugar can make strokes worse.

Well, that was a long answer to a short question, wasn’t it? The takeaway is that, no, it doesn’t appear that a low—or even a lot of lows—can trigger strokes. But if you have frequent lows, and then have a stroke, it sure looks like your risk for an unhappy ending is much, much higher.

Like, by 70% or so.


This is not a medical advice column. We are PWDs freely and openly sharing the wisdom of our collected experiences — our been-there-done-that knowledge from the trenches. But we are not MDs, RNs, NPs, PAs, CDEs, or partridges in pear trees. Bottom line: we are only a small part of your total prescription. You still need the professional advice, treatment, and care of a licensed medical professional.