Insulin 101

A comment from a friend recently reminded me how little many people understand about Type 1 diabetes. And what people know from TV/movies is usually wrong! Honestly after living this many years with Type 1, I forgot how much I didn’t know before my diagnosis! It’s all second nature to me now, I don’t usually have to think about what I’m doing. As simple as I try to make these blog posts, it’s entirely possible I am still talking over your head. Please send me questions if that happens, I can always fix a blog to make it easier to understand!

Today we are going back to insulin 101. What is insulin and how does it work? Insulin is a hormone made in the pancreas. When you eat food, particularly carbs and sugars, they are broken down by the liver and turned into glucagon. That glucagon enters the blood stream as glucose and is carried to the cells where insulin acts like a key to allow the glucose to enter the cells for energy. Without insulin, the glucose can’t enter the cells and builds up in the bloodstream. A finger prick will tell how much glucose is in the blood, 80-100 is normal (although a post-meal spike as high as 150 even in a healthy person isn’t unusual), a diabetic can have a blood glucose (aka blood sugar aka BG) as high as 800+.

When not enough carbs or sugars are eaten for the liver to produce glucagon, the body will break down fat cells and sometimes muscle cells to produce glucagon which is why low carb and keto diets are popular for loosing weight and fat. Outside of meals, the liver releases small amounts of glucagon 24/7/365 to provide energy to the cells needed for the body to function. So a healthy pancreas produces just enough insulin to match the glucagon released by the liver, too much causes low blood sugar and too little causes high blood sugar but for the non-diabetic your body keeps you perfectly in range!

For Type 1 diabetics who’s pancreas either makes too little or no insulin, it needs to be injected to keep BG in range. For those on insulin injections/shots, two types of insulin are needed. Basal insulin slowly releases to match the constant slow release of glucagon and a fast acting insulin is needed at mealtimes with food. For those on an insulin pump, only a fast acting insulin is used as it slowly releases 24 hours a day mimicking what a basal insulin does (and what a healthy pancreas does).

Although it is called “fast acting” insulin, most take 20 minutes after injecting before working. A bolus of insulin is given at mealtime and whenever a “correction” is needed because BG is too high. Mealtime insulin is calculated based on how many carbs will be eaten (so I have to decide before the meal how much I will eat). That fast acting insulin circulates in the bloodstream on average for about 4 hours but everyone is a little different, for me it is closer to 3 hours. Most diabetics try to “pre-bolus” for meals, taking insulin 20 minutes before eating to lesson the spike from eating.

So when insulin is given either with a meal or as a correction, it takes 20 minutes to start working and more insulin can’t be given until 3-4 hours later. During that window it is called “active insulin” or “insulin on board” (IOB). Giving more insulin during that time without eating more carbs will likely cause BG to go too low. But sometimes it can take almost all of that time to bring BG back into range. Sometimes frustration from high BG that isn’t responding leads to a “rage bolus”, giving more insulin than recommend in an attempt to budge a stubborn high. Rage bolusing is NOT recommended and in certain situations can be dangerous. But we have all done it at times.

I have my continuous glucose monitor (CGM) alerts set that I will get an alert every hour when I’m too high. I do that because I otherwise forget to check if my BG has come back into range and I want an idea of how long my insulin is taking to work. But if I have already had a bolus of insulin in the last 3 hours, there is nothing further I can do to treat the high BG until I no longer have any active insulin (which I can quickly see on the screen of my insulin pump). So sometimes I turn off an alert without doing anything because I can’t do anything more yet, it’s just on to keep me aware of where I am.

As with everything about Type 1 diabetes, each diabetic knows their own body best, how it responds, what works best, what is most successful. No one follows all the “rules” strictly but uses experience and intuition to decide how to dose insulin and when. Ask questions but also know that each diabetic you know might do things a little differently. But hopefully you have a little better knowledge now of how insulin works. And take a moment to thank God if you have a healthy functioning pancreas ❤️