Having good insulin absorption is the unspoken foundation of managing your diabetes well.
Think about it.
Even if you have the “perfect” settings that magically change whenever you change, you eat the “perfect” foods which are distributed between the “perfect” macros, and you keep to the “perfect” portion sizes and “perfect” timing. Let’s say you get 7+ hours of “perfect” sleep (which is never disrupted by any alarms…yeah…right), you get in the “perfect” amount, intensity, and balance of exercise, all while staying “perfectly” consistent.
Just writing that makes me feel queasy because perfect is not reality which is why it is used in quotations.
However, the point being, that even if you reached “perfection” in all the areas that need attention for optimized diabetes control, guess what? Without good insulin absorption, your blood sugar numbers will be lackluster at best.
So yes, this article is dedicated to helping you understand the factors that affect insulin absorption and how you can find the right method for injections and pump sites to improve your insulin absorption.
First off, you can get poor insulin absorption from injections (syringes/pens) AND pump sites. So in this article, we will go over the most common 10 factors that can affect your insulin absorption.
Before we get into the factors, you first need to be aware of Subcutaneous Blood Flow (SBF). Which simply means the flow of blood just below the skin which is where the insulin is injected and starts making its way throughout the body to take the glucose from blood into the cells. By removing glucose from the blood into the cells, is how our blood sugar is lowered. For simplicity, we will state SBF as blood flow throughout this post.
Factors that increase the blood flow at the injection site will increase insulin absorption and therefore make the insulin work faster and better. Which is what we want!
On the other hand, factors that slow this flow will decrease absorption which can cause stubborn and even unpredictable blood sugar. By having consistently poor absorption, it is near impossible to figure out your right settings and dosing amounts, and to stay in target range safely.
Below is a detailed list of 10 different factors that greatly affect blood flow and the rate of insulin absorption. By understanding these factors, hopefully you will gain insight to improve your management without dubious amounts of extra effort.
10 Factors that Affect Insulin Absorption
But number 5 is my favorite…
Lipohypertrophy is a big one and is the term used to describe the lump under the skin that develops from fat build up due to many insulin injections or pump sites. These lumps can be unsightly and may even be mildly painful. The best way to avoid developing lipohypertrophy in the first place is by rotating your sites, and if you are using a pump, not to extend over the recommended 3 days of use.
One reason why lipohypertrophy delays insulin absorption is that it can decrease blood flow. Also, by continuing to use lipohypertrophic areas, you can cause not only delayed absorption, but unpredictable absorption.
Delayed AND unpredictable absorption can cause someone to overtreat during the day because their blood sugar is staying stubbornly high, then all of the sudden, as if they stars align just right, “BAM!”, insulin stacks and starts working all at the same time. And now you are forced to gobble down spoonfuls of sugar, and nothing is more annoying, especially if you are trying to watch your weight.
When this happens at night, it is completely irritating, but ever worse, down right scary at times.
Take a moment and imagine with me…
It’s 2 AM and you just hit REM, you’re dreaming of happy things and finally getting the Zzzzs you so desperately need. Then, as if it was perfectly time to wreck your life, the “siren” alarm.
Startled half to death, you abruptly awake, confused and incoherent. You ambly begin to feel around for tubes of glucose tabs or crinkly fruit snack wrappers stuffed in your nightstand. You then stuff each tab or fruit snack in your mouth with complete and utter annoyance. Then, out of fear that the amount wasn’t good enough, you inhale an extra dose “just to be sure“. As you try to make yourself comfortable so you can get a couple more hours, you lie there debating whether you should or should not brush your teeth from eating all that sugar. Finally, you drift back asleep, and hope that the siren war has ended for the night.
If you have type 1, you likely are well aware of this scenario.
My point, unpredictable and stubborn absorption is super annoying and can be dangerous, especially if it induces nocturnal hypoglycemia (low blood sugar during the night).
If you do feel hardness or bumps being formed from injection, it is best to completely avoid such areas so they can adequately heal. Depending on the degree of damage, you should avoid such areas for 2-3 months or more. Over the 2-3 months, you can feel the areas to see how the lipohypertrophy is softening and feeling more normal (no lumps or pain).
TAKEAWAY: Watch for lipohypertrophy (bumps and hardness under the skin). If you do feel lipohypertrophy, avoid these areas until the damage has healed (which can take 2-3+ months depending on the damage severity).
If you are a pump user, make sure to rotate and change out your sites every 3 days. Having a site in longer than 3 days can increase the likelihood of building up lypohypertrophic areas. If you have lipohypertrophy in ALL your pump spots, consider going on a pump break. Pump breaks can be anywhere from 2 weeks to a full year. Just make sure to work closely with your provider or a diabetes educator to stay in control during a break.
Below is a cartoonized representation of lipohypertrophy (small, medium, and large).
Venn-Wycherley, Alison. “Suspect, Detect and Protect: Lessons from a Lipohypertrophy Workshop for Children’s Nurses.” Alison Venn-Wycherley, Nursing Children and Young People, journals.rcni.com/nursing-children-and-young-people/suspect-detect-and-protect-lessons-from-a-lipohypertrophy-workshop-for-childrens-nurses-ncyp.27.9.21.s23.
3) Skin Temperature
Increasing skin temperature increases insulin absorption. You may have witnessed this when you have high blood sugar and high insulin on board (IOB), but then take a hot shower or bath and then find your BG plunging and FAST. The increased body temperature increases the rate of the blood flow which then causes the insulin to move faster which accelerates insulin absorption. Think of the difference between pouring cold vs hot syrup. When liquids are warmed (which includes blood), they move at a faster rate.
However, it’s important to note that a sunburn can actually raise blood sugar due to increased stress and inflammation from the burned skin. As you are likely well aware of the annoying effects of stress on your blood sugar (emotional and physical), sunburn is just another form of physical stress on the body which is why it can increase insulin resistance and make your blood sugar more stubborn to treat.
TAKEAWAY: If your blood sugar is high, and you have insulin on board, take a hot shower or bath to increase blood flow which will make your body more quickly absorb the onboard insulin.
4) Local Massage
A massage can lower stress, which is helpful to reduce general insulin resistance, but it can be especially helpful in the physical sense by increasing insulin absorption. Simply, the act of spreading the insulin with a massage essentially “rubs in ” the injected insulin which then increases the surface-to-volume area. Therefore it is especially effective to massage or workout the area at the place of injection if you need to speed up insulin absorption for high blood sugar. Another example of this is by injecting insulin in a leg, then going on a walk. Somewhat similar to a massage, the act of walking is making the muscles move and “massage in ” the injected insulin. However, understand that purposely exercising the muscle with the injected shot is not recommended for general use, but serves as a catalyst if you need to bring down a high quickly.
TAKEAWAY: If you have a high blood sugar, you can actually massage the area where you took the injection to increase insulin absorption to more quickly lower your blood sugar
*BONUS* It’s a great excuse to get a massage!
5) Injection Site
The site of injection will have a great effect on how fast (or slow) your body will absorb the insulin. Typically, areas that are higher in subcutaneous fat are going to have less vasculature and therefore decreased blood flow and insulin absorption speed.
Below is the order in the areas that are known to be better for consistency and good absorption (from best to worst).
#2 Back of Arms
#3 Back or Flank area (closer to the spine)
#5 Buttocks (dead last)
One reason that the location dictates the rate of insulin absorption is the level of subcutaneous fat and vasculature. The stomach has subcutaneous fat (the amount depends on the person), but has great blood flow. The arms have decent muscle tone which improves access to good flow for better absorption. However, the buttocks and the thigh tend to less blood flow and can be more fatty areas which is the perfect storm for poor insulin absorption. You have probably witnessed this, but now you have a better understanding on the why.
Personally, I don’t like using my stomach. However, I am on the leaner side, so my back is where I can pinch, but I still have muscle tone and therefore decent vasculature. I have found that if I stick my pods closer to my spine, I have better blood flow, versus going closer to my buttocks or love handle areas which are higher in fat and lower in good blood flow.
And to be completely candid here, it’s nice putting my pod and dexcom on my backside so I feel a bit less of a cyborg. Believe me, I can talk diabetes all day and to anyone, but it’s nice not broadcasting to the whole world everywhere I go, “HELLO, I HAVE DIABETES” by giving my pod and CGM prime real estate on a visible arm or using a pump with a tube for everyone to see. If you like to show off your gear, more power to you! I love the sass.
Working with patients and having Type 1 myself, my advice to you is to stick to a place that is firm (from muscle), but also pinchable (from subcutaneous fat). This balance will allow for good absorption that is consistent.
Also, you can get creative with your site location(s). Especially if you use Omnipod. I have some patients that have found that their upper back or even their calves work super well. Mix it up until you find the area that works well for YOU.
Another point I want to stress is that there are multiple pump infusion set options for a reason. It’s not a one-size-fits-all ordeal (unless you use pods).
My Frustration Story from Using the Wrong Site
I had a year of more lackluster control, despite my heroic efforts, and after a lot of trial and error (emphasis on the error), I found that my root cause was poor insulin absorption issues from the WRONG pump site for my body. After switching between the most popular sites (all were wrong for me), then going on a pump break with syringes for almost a year, I then went back on Tandem and tried the super scary Tru-Steel infusion sets and fell in love! I wish that I had tried them sooner, but I didn’t know better and was scared of the steel. Learn from my mistakes. Try them ALL out and don’t be scared of the steel.
TAKEAWAY: Site location and the right pump site are critical for good diabetes management. I’m talking points different in A1c for the same (or even less) amount of work with your diabetes. Having the right site for your diabetes can make or break your control. Please, for your sanity, learn from my mistakes and if you have poor insulin absorption and you are using a pump, work with your provider or diabetes educator to investigate your pump site options!
6) The Amount of Insulin Dosed
You may or may not be aware of this, but actually the amount of insulin in a dose affects the insulin absorption. How it works is that the larger the dose, the smaller the surface-to-volume ratio which decreases the absorption of the injected insulin. Meaning big doses causes for slower absorption. However, that doesn’t mean don’t dose the full amount that you need for your carbs and/or correction, but if you split that dose, it could allow for faster insulin absorption.
TAKEAWAY: What I do, is I make mini small boluses as I eat which allows for a more intuitive eating approach and it allows for faster absorption from the injected insulin. I start my meals by doing a pre bolus which helps get the insulin working before my meal and helps me reach a blood sugar range I want to be before introducing food.
In this pre bolus, I also add the dose needed to cover the carbs I know I will eat. However, the moment when I know I am eating more than what I covered with initial pre bolus, I do another bolus. Sometimes I do as many as 5 mini boluses for a single meal. This approach isn’t ideal for someone who takes shots, but is worth splitting up your dose to at least 2-3 injections especially if you are more insulin resistant or are having absolute hay day with carbs at a meal!
As a side note, I use Fiasp, which supposedly has a fasting onset which theoretically allows me to dose at the meal rather than having to do a pre meal dose. To be frank, I cannot tell much of a difference compared to Novolog, however it does seem to work a little faster. Below is my personal ranking of fast acting insulin to use in a pump.
#2 Novolog (super close second)
#3 Humalog (dead last)*
*Humalog is still considered a fast-acting insulin, but has a slower onset compared to Novolog. However, if you use U200 Humalog (which is twice the concentration of U100), U200 typically has a faster onset compared to Humalog U100, possibly even faster than Novolog, but comparable or maybe just a bit slower than Fiasp (personal and patient experience here).
SIDE NOTE: If you use have a high total daily dose, consider working with your provider to switch to U200 (though you may need a prior-auth).
If you are confused about exercise and the effects if it has on blood sugar, you are not alone. As you have likely experienced, cardio (aerobic) exercise makes the current amount of insulin work well, therefore if you ate a meal, dosed your usual amount, then went for a long walk or slow jog, you can expect a fast drop in BG, and to be inhaling glucose tabs like there’s no tomorrow. Reasons that cardio exercise lowers blood sugar quickly is that glucose is being burned up during the workout which of course lowers blood sugar and that exercise speeds up the blood flow rate pumping throughout your body. The faster the rate with cardio-based activity, the faster absorption for insulin.
As a note, and as I go into much greater detail on the effects of exercise on blood sugar in the related post on this page, generally speaking, aerobic exercise lowers blood sugar after about 15 minutes of activity, but anaerobic (intense) exercise can actually spike blood sugar (but then decrease insulin needs throughout the day). To learn more, you can check out that related post.
8) Other Comorbities & Complications
A comorbidity is a disease or condition that coexists with a primary disease such as diabetes, but stands on its own as a specific disease. These diseases or conditions can be physical or mental. Common comorbidities for people with type 1 diabetes are other autoimmune conditions such as hashimotos or celiacs disease.
Depending on the type and pathophysiology of the comorbidity, there can be decreased blood flow and other factors at play that reduce insulin absorption. A common one that is brought on by many years of having uncontrolled type 1 is gastroparesis which is the act of delayed or poor gastric emptying. We will not spend a whole lot of time in this article on comorbidities with type 1, but if you do have other comorbidities along with type 1 that are making management difficult, work closely with your provider or diabetes educator to get the personalized help that you need to stay in control and live your life.
To keep it simple, smoking makes blood sugar control more difficult for a variety of reasons, however for brevity sake, just know that smoking is assoicated with insulin resistance and it also causes peripheral vasoconstriction. As you can assume, anything that constricts blood flow would cause delayed insulin absorption. So for many reasons besides diabetes, quit smoking and if you need help doing so, work with your provider for guidance and the support you need.
When it comes to obesity and its effects on insulin absorption, the topic is long and we will not be diving into all the mechanisms related to poor absorption and insulin resistance and their relation to obesity. However, understand that the key components from obesity that not only decrease insulin absorption, but increase insulin resistance are related to reduced subcutaneous blood flow, but also systemic chronic inflammation, increased cortisol levels, and the type of fat. What I mean by this is someone who holds fat around their midsection like an apple (android) vs someone who holds fat all over like a pear (gynoid) will have different insulin resistance.
Someone with more abdominal obesity indicates that they likely have higher visceral fat (AKA organ fat). This is likely due from insulin resistance in the liver that drains directly into the liver (through the portal vein) and with the increased fat from the liver, as well as increased cortisol, hepatic insulin resistance, more organ fat around the midsection accumulates which thus causes someone to develop an android (apple) shape build.
TAKEAWAY: There is a lot of cover relating to obesity, inflammation, cortisol, stress, poor insulin absorption and resistance, however, know that by keeping active, and eating healthy foods, you can obtain more of a pear rather than an apple shaped, which is related to lower visceral fat, better overall health and metabolism, and increased insulin sensitivity.
The purpose of this post (and all my posts) is to be educational for you. As a Dietitian and a Diabetes Eduator, I write these posts in hopes of helping you learn how to better manage your diabetes and feel in control of your life. As each of us share our knowledge and support for one another, we can all alleviate each other burdens and improve our health and happiness. We’re in this together.
Lastly, and as always, if you need help with your diabetes management or you are suffering from poor absorption and don’t know how to troubleshoot what’s going wrong (perhaps a bad pump site for you), don’t hesitate to write me a message or schedule a consultation for us to work together. Like you, I understand how scary, annoying, and endless diabetes can be. Somedays you just feel burnt out and you need someone who not only can help you but understand where you are coming from.
I practice as a Registered Dietitian Nutrition, a Certified Diabetes Educator, and I also have diabetes. I have two kids, and a life (I like to think so at least), and I know that either you control diabetes, or diabetes will ultimately control you.
No matter where you are in your management, remember, it’s not ever about perfection, but progression. We are all growing and learning everyday.
Ariel Warren, RDN, CD, CDCES and T1D