What is insulin?
The body’s own insulin is a blood sugar-lowering hormone that is produced in the pancreas. It plays a central role in many metabolic processes in the body, especially in blood sugar. It is therefore crucial in diabetes mellitus: patients’ abnormally high blood glucose levels are either due to the body producing too little insulin or to the fact that the insulin that is produced is not working properly.
In the first case, this results in an absolute insulin deficiency. This is typical of type 1 diabetes: this form of diabetes can only be treated with insulin preparations. This means that the missing hormone must be regularly supplied from outside (insulin therapy). Various insulin preparations are available for this purpose.
How is insulin administered?
Today, diabetics who require insulin inject the insulin themselves using wafer-thin needles and an insulin pen that looks like a fountain pen. More rarely, an automatically operating insulin pump replaces the manually administered syringes.
What types of insulin are there?
The insulins administered in diabetes therapy must mimic the necessary hormone action in the patient’s body. This is the only way to reduce elevated blood glucose levels and prevent secondary diseases (such as diabetic foot or diabetic retinopathy).
The insulins used for diabetes therapy can be divided into animal insulins (such as porcine insulin) and artificial insulins (human insulin, insulin analogs) depending on their origin.
In the past, diabetics were treated with insulin isolated from the pancreas of pigs and cattle (porcine insulin, bovine insulin). However, the human immune system often reacts to the foreign substance by producing antibodies. This impairs the effect of the insulin. This is why porcine and bovine insulin are used less frequently than in the past.
Genetically engineered human insulin is identical to human insulin. It is the most commonly used insulin in diabetes therapy. Animal insulins and human insulins (without the addition of effect-prolonging substances) are also referred to as normal insulins because they have the same structure as human insulin.
The various insulins are also classified according to their duration of action and their action profile. How and when an insulin preparation is used depends on these two characteristics.
The onset of action of an insulin depends on various factors, including the place of injection.
Short-acting insulins
They cover the insulin requirement at mealtimes (bolus). This is why doctors also refer to them as bolus, mealtime or corrective insulin.
Normal insulin (formerly: old insulin)
The effect starts after about 15 to 30 minutes. The insulin must therefore be injected half an hour before eating (injection-eating interval). The effect reaches its peak after one and a half to three hours. The total duration of action is about four to eight hours.
Insulin analogs
The effect often occurs after about five to ten minutes. In contrast to normal insulin, there is no time interval between injecting and eating. The maximum effect is achieved after one to one and a half hours. Overall, these insulin analogs have a shorter effect than normal insulin: their duration of action is around two to three hours.
Intermediate and long-acting insulins
They cover the basic need for insulin independent of food (basal) and are therefore also called basal insulins.
Intermediate-acting insulins
NPH insulin can be mixed stably with normal insulin in any ratio. There are therefore numerous insulin preparations on the market with constant NPH/normal insulin mixtures. However, the two components are often only mixed together in the syringe immediately before injection.
The effect of intermediate insulins is not uniform. This sometimes leads to hypoglycaemia at night when the insulin reaches its maximum effect. In the morning, on the other hand, when the effect wears off, increased sugar levels are possible.
Long-acting insulin analogs
The duration of action of long-acting insulin analogs is usually up to 24 hours. They therefore only need to be injected once a day. In contrast to intermediate-acting insulins, these insulin analogs act relatively evenly over the entire period and do not have a maximum effect. As a result, there is less risk of hypoglycaemia at night and sugar levels remain lower in the morning.
Insulin analogs are easier to use than delayed human insulins. They are available as a clear, dissolved liquid and are therefore easy to dose and adjust the blood sugar very evenly. Human insulins, on the other hand, settle as crystals in the ampoule (suspension). They must therefore be mixed carefully before each injection in order to avoid dose fluctuations.
Mixed insulins
How does insulin work?
A healthy pancreas releases small amounts of insulin evenly throughout the day. They cover the basic need for insulin and thus maintain vital metabolic processes (basal rate).
The pancreas also releases additional insulin with every meal in order to utilize the sugar from the food (bolus). The amount of insulin released by the pancreas depends on eating habits, physical activity, time of day and other circumstances (such as acute illnesses).
How much insulin a diabetic has to inject to cover the basal rate and bolus varies from person to person. The amount also depends on the carbohydrates ingested with food, which are given in bread units (BE) or carbohydrate units (KHE).
More information on insulin and BE can be found in the article Diabetes – bread units.
Insulin and fat metabolism
Overdose of insulin
The aim of insulin therapy for diabetes is to normalize blood sugar levels. If insulin is overdosed, there is a risk of hypoglycaemia – which can even be fatal in severe cases.
