What Affects Insulin Absorption

Of all the factors that seem to impact our blood glucose on a daily basis, insulin absorption rates can be one of the trickiest to manage. Most of us know that insulin is absorbed at different rates depending on where it is injected (or where the infusion set is placed if you’re pumping). The stomach is generally the area that provides the fastest absorption, followed by the upper arms, thighs, and upper buttocks. This is general knowledge for most of us, and if the list were really that simple, it would be fairly straightforward. But this is diabetes — it’s never straightforward!!

There are a host of other factors that affect how quickly insulin is absorbed into our system, and many of them can be almost impossible to detect (but some planning and educated guessing can help). Nevertheless, we’ve got to make our best effort to take these factors into consideration when we manage our blood glucose, because the effects of absorption are very real, and can lead to maddening high or low blood glucose readings that seem to “come out of nowhere.”

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Let’s start by listing what exactly impacts absorption:

1. Site selection. As noted above, the abdomen is generally the “fastest” site for insulin to absorb, followed by the backs of the upper arms, outer sides of the thighs, and the upper buttocks or hips.

2. Subcutaneous tissue (connective tissue and fat) versus muscle. Insulin should be injected into the subcutaneous tissue layer just under the skin. Our insulin needles are designed to inject insulin into this layer. If insulin is injected into muscle, it will absorb significantly faster. This is why some of us pinch up our skin when we inject — it helps ensure that we’re not injecting into muscle, but into the fatty layer we’re supposed to inject into.

3. Too MUCH subcutaneous tissue (come on, diabetes!!!!). In another maddening little diabetes quirk, insulin can also be thrown off when we inject into a layer of fat that is DEEPER than ideal. Remember how the abdomen was supposedly the quickest route? Well, if you inject in the front of the abdomen, and happen to have a little bit of extra padding there (as I certainly do — it’s on my list of things to take care of), that will slow down the absorption. So you want to get into the subcutaneous tissue, but you don’t want to inject into a thick layer of it. See?!? Maddening!

4. Scar tissue. Oh, scar tissue, how I hate you!! Scar tissue can wreak havoc with your absorption. Think about this for a minute — if you take multiple daily injections, you are “stabbing” yourself 4–5 times every day! Yes, it’s a tiny needle that you barely feel (usually — sometimes you get a “stinger”), but it is still an “injury” as far as the body is concerned. And the body responds by building scar tissue. Scar tissue is your body’s version of an iron gate meant to protect the injured area. Over time, scar tissue can build up, and entire areas of your body can become basically “unusable” for injections or infusion sites. Scar tissue will significantly derail absorption. I have had times when I know I’ve hit scar tissue, and a shot of insulin will have no effect for two hours, shooting my blood glucose into the stratosphere. I take my correction dose and it starts to slowly fall back to earth. But then, seemingly out of the blue, the initial insulin FINALLY makes its way through, and I go low as the correction dose and the initial dose from hours ago hit my system simultaneously!

5. Temperature. As noted on this page from BD, heat, such as from a hot bath or sauna, can open up blood vessels, increasing the insulin absorption rate, while cold can decrease the absorption rate.

6. Activity level. Your level of physical activity impacts how quickly insulin is absorbed. I’ve heard of people who will always go for a half-hour walk after a high-carb meal, because they know that it will help speed up the insulin absorption and head off an unwanted high peak in glucose level. Physical activity is kind of a “double-impact,” actually, as it causes your body to burn through the sugar more quickly AND speeds up the absorption of insulin. As we all know, exercise pushes us low faster than just about anything else we can do.

There are probably some factors I’m leaving off this list (and if you know of them or have experienced them firsthand, please share with our readers in the comments), but I’m starting to run out of space here. And we haven’t even gotten to what to DO about any of the items on this list. So next week, come back and we’ll talk a little bit about what we can do to manage insulin absorption. Like I said, it’s often a matter of making educated guesses, but there are things we can do. See you next week!

Eating a low-carb diet may help reduce both hunger and food cravings, according to a small new study. Bookmark DiabetesSelfManagement.com and tune in tomorrow to learn more.