Blood Sugar Spikes 18 To 24 Hours After Exercise

I’m putting this out to/for my fellow type 1 diabetics out there.

It is well-documented that exercise in excess of 80% of threshold (think VO2 max) raises blood sugar rather than lowering it. If you go for a light jog, your blood sugar will go down. If you push hard and go for a super-fast run, you’ll probably end up raising your blood sugar. If you didn’t know this, then now you know. How do you use this information: if you plan on doing a very strenuous workout, do not take extra carbohydrate before exercising, and do not reduce your basal rate or long-acting dose. Test after exercising and correct as necessary.

But here’s something I cannot find any information on: When I engage in a very long bout of exercise – for example, a 10-mile long run – my blood sugar certainly comes down, but I have noticed a tendency to experience a rather large blood sugar spike 18-24 hours afterward.

I didn’t even notice this tendency until this morning, when I was reviewing my blood sugar log. Over the weekend, I had had what I classified as a “very mysterious high.” I remembered that this had happened a couple of weeks back, so I scrolled up and was amazed by how similar the readings were. I had had a long run on Saturday at about the same time of day; my before-breakfast readings were within 5 mg/dL of each other, and in both cases by 11 AM, my blood sugar had shot up beyond all explanation. In both cases, this was followed by near-identical lunches. Finally, in both instances, in the late afternoon I experienced hypoglycemic sensations, tested, and found I was in the 80s (mg/dL). Precisely the same experience, weeks apart.

Then I checked deeper into my log history and found a few more recent examples. That is, I logged blood sugar readings that followed the same pattern. It has been too long for me to remember the details of those older examples.

Please, please, PLEASE if for some reason you are a diabetic who sees this blog post, please leave me a comment and let me know whether you’ve noticed a similar phenomenon.