My understanding is that diabetics have a pancreas that does not produce insulin or the body has stopped reacting to insulin, which mean they can get really high blood sugar because nothing metabolizes is.
But why does that cause diabetic people to also get low blood sugar more often than non-diabetics? If I eat a cake, my body produces a bunch of insulin to metabolize, then I go work out for an hour, my blood sugar won’t be as low as a diabetic who did the same.
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I’ll do my best to throw my 2 cents in since nobody has mentioned glucagon yet!
To start, when we talk about blood sugar, we’re specifically referring to the sugar known as glucose. This is the sugar that is readily available for energy production in cells in the energy producing pathway known as glycolysis which converts it to pyruvate, which is then further broken down in the citric acid cycle (Krebs cycle) to produce energy. When patients with diabetes check their blood sugar, they are using a meter to check glucose levels specifically.
In the body, you’ll often find more than one hormone responsible for functions that can help balance each other out to maintain homeostasis (the body’s ability to keep things approximately even despite ever changing conditions). In the case of glucose metabolism, you have insulin which helps to store glucose in the form of glycogen (short term storage) and fat (long term storage). The opposing hormone is glucagon, which helps to mobilize these energy stores by breaking down glycogen stores in the liver, mobilizing fat stores and releasing fatty acids, and stimulating gluconeogenesis (the production of glucose from certain non-sugar substrates). Glucagon is naturally released from the pancreas in response to stimuli such as low blood glucose, exercise, or fasting conditions. This makes sense, because these are all good times to want to make more energy stores available to the body.
In healthy individuals, the pancreas is able to produce these two hormones at appropriate times in response to blood glucose levels and other hormonal factors to keep glucose in a tightly controlled range. Too little glucose and you could experience sweating, hunger, fatigue, or end up losing consciousness. On the other hand, too much glucose leads to chemical reactions that produce inflammation that can damage the body and lead to nerve pain or loss of sensation, increased risk of heart disease, and problems with the kidneys, among other things. Patients with diabetes either aren’t producing insulin at all anymore (Type 1) or are effectively not producing enough insulin to keep up with the body’s glucose levels (Type 2, AKA insulin resistance).
To combat this loss of insulin effect, patients with diabetes can use medications to increase the amount of insulin released, inject extra insulin to meet their bodies demands, or other various mechanisms to reduce blood glucose. The problem comes from the inability to control exactly how much insulin is present and active at any given time. If you have too much insulin, it will lower blood glucose too quickly and not give the body enough time to produce glucagon and counteract the effects. In a healthy individual, this wouldn’t occur due to hormonal feedback loops that prevent dumping insulin all at once; the pancreas is able to release the right amount at the right time and just lower it enough. One medication that can be used to treat low blood sugar though is… Glucagon! While this used to be available only as an injection kit that needed to be mixed and injected, more recent devices have been made that allow for administration either with an auto-injector (now you don’t need to mix it first) or through a nasal spray (fast and easy administration).
Modern diabetes medications generally have a lower risk of causing hypoglycemia (low blood sugar) due to the different pathways involved (some medications cause you to pee out glucose for instance) and due to improved ability to monitor sugars and accurately dose insulin. In fact, closed loop monitoring systems that detect your blood sugar and release the appropriate amount of insulin are available and can help to prevent hypoglycemic episodes from happening as often.
The root problem at the heart of your question is ultimately because the medications prescribed for patients produce a relatively static response whereas your body is a dynamic and ever changing system. If the dose given at any particular time is more than what your body needed, well… Now your blood glucose is going to be too low.
TL;DR
The pancreas isn’t working properly, so you’re manually trying to correct for something that’s dynamic and always changing. Sometimes you mess up and overdo it. Then you get low blood sugar.
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