I have been a type 1 diabetic for 23 years and strangely enough I still don't have any idea how long it takes for my fast acting insulin to kick in. I tested today at lunch and I was at a high of 21.2 mmol/L. I believe that I had breakfast without taking my insulin. After something being like second nature it's funny how you can forget if you actually took it or not. Anyways, I went for a 7.5km run and it took me 41 min. I thought that my blood sugar would be relatively lower but to my surprise it has only gone down to 19.0 mmol/L. This is what made me wonder how long does it take for insulin to kick in? Should I take more? I take Novorapid; 1 unit for each 10g of carbs ingested as well as Lantus before I go to bed. I've looked it up online but of course like everything else the answers vary from one side of the spectrum to the other.
I'm hoping that maybe one of you well educated diabetics or diabetes worker can help me out.


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It's supposed to start working in 10 or 15 minutes, but I remember my endo telling me if you work out when too high, you end up higher. It's something to do with stress placed on the body during exercise. For me, once I'm that high from missing a bolus, it takes a lot longer to come down regardless of exercise. It usually results in over correcting and hypos later unfortunately. Hope it's different for you.


Thanks Charlene. You are the second person to tell me about the highs related to exercise. I've never been told that by any of my doctors despite having been in competitive sports for the last 15 years! Urgh! I really need to get myself a new diabetes doctor.
Thanks again for your input.

Here is a chart with some of the various insulins on that compares the kick in time, peaks and duration. I use Apidra and it takes 20 minutes to kick in for me. Just because someone else has a 20 minute wait doesn't mean that will be the case for you.


Seems like a simple question, but there are actually different sides to it.

How fast it 'kicks' in depends on what type, how injected (syringe, pump, pen) and location. But a general average, for the 'rapid'/bolus insulins is 10-30 minutes.
But if your BG is currently rising, sometimes it's hard to tell when it actually kicks in.

The 2nd part of the question is really how effective is it. For the same person, 1 unit may sometimes drop blood glucose 100 pts, and other times 50 pts. That is sometimes referred to insulin resistance or insulin sensitivity. Most people have a ISF - Insulin Sensitivity Factor, which is the AVERAGE number of pts their BG will drop for 1 unit. And often it will be different in the morning, afternoon and evening for a given person.

In general, the higher your current BG is, it will take MORE to bring down the same number of pts, because often high BG makes you more insulin resistant.
Exercise can make you more insulin sensitive, but certain exercise is the opposite, if adrenalin is released. Hormones and stress tend to make you more insulin resistant.

You mention you take 1 unit for 10g carb, but do you also know your ISF number ?

When you realized you ate breakfast w/no bolus, did you take any insulin before you ran ? If not. all you had was your basal (Lantus) in your system. To bring down a high BG, you need more than your basal. Insulin is referred to as the 'key' that unlocks the door of cells, to let the glucose in. When you have low insulin, and then exercise, your body will use glucose stored in muscle cells, since it is unable to get it from blood.

Many doctors recommend to not exercise with BG over 240 (10.3), and to first take a correction to get it down. I have found that light exercise (walking) plus correction is best, along with drinking fluids.

BG -> 180 mg/dl = 10.0 mmol/L

Thank you MegaMinxX, your post was very helpful to me. I don't know what my ISF is but it is absolutely something that I will look into now. I've been having trouble with keeping my BG at an acceptable level and I really need to find what works best for me. Thanks again :)

I think that MegaMinxX hinted at this. The insulin may have started working by just stopping your BG from going higher. And then it took longer to actually start bringing down your BG. Actually your question is a good question and not easily measured as the other posters mentioned many of the factors that can affect the insulin lowering your BG.

I find it takes much less insulin to stop me from going higher than it does to bring me down once I'm high. So if I forgot my breakfast bolus, it might take me two or three times the amount of insulin to bring it down than if I'd just taken the proper meal bolus.

No one said it was easy to figure out Type 1....

Lathump - wasn't until I got my CGMS that I realized how frequently my correction initially slows down the rise or flattens my BG, rather than an immediate drop.
With CGMS and seeing the trend, I can make a better calculation for the correction amount. When I was taught to calculate a correction bolus, they never mentioned that.

As for being hard to bring down a high, my analogy is to think of my blood vessels as crowded streets at rush hour, and the insulin molecules are like emergency vehicles trying to get through to let the glucose into the cells. We call that grid lock !

As with everything in D, YDMV, your diabetes may vary. How insulin acts in me most likely will not be the same with you, but for me I just switched from humalog to apidra. While my CDE said they are equivalent in action and activity, I have found that humalog acts like a bull dozer, in 15 minutes it is already lowering my blood sugar, and if I am not high enough to begin with, or I do not eat enough carbs to cover the bolus, I will invariably end up with a hypo and it continues to act for close to 5 hours. In contrast, apidra acts more like a slow train, it takes longer to start working probably close to 1/2 hour, and does not cause the huge swings in my blood sugar. It also clears out of my system a lot faster, so within 2.5 hours it is gone. So if I totally mess up the carb calculation I can always correct a bit sooner with apidra. You said you have your I:C ratio at 1:10 but is that the same for every meal ? And also do you have an ISF or correction factor for the times your blood sugar is that high ?

Ok, I'm confused. You talk about running, but you don't mention correcting. Did you take insulin to correct your high?

With a blood sugar that high (378) it's important to take correction insulin according to your ISF. I also have heard it is not appropriate to exercise when you are extremely high, though I couldn't explain the science.


There's a risk of DKA when exercising with high BG due to dehydration & pushing BG even higher from the effects of adrenaline.

Thanks for the science, Gerri. Me, when I'm high I just take insulin! I still don't understand if the OP was attempting to correct that high without using insulin!

You know my philosophy about running:)




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