About insulin in type 1 diabetes 

Insulin is a natural hormone produced by the pancreas. In type 1 diabetes, not enough insulin is made naturally, so insulin has to be injected. Insulin comes in different types, with a variety of dosing regimens. Basal or background insulin supplies low-level insulin to keep body processes in balance, while bolus insulin is also used for extra needs at mealtimes. Insulin is injected under the skin, not into a vein, and is usually delivered by syringe or pen injector. Insulin pumps are also available, supplying continuous insulin doses, but these pumps are usually not subsidised (not funded).

Work with your diabetes team

If you are newly diagnosed with Type 1 diabetes or you are thinking about making a change to your current insulin, always work closely with your specialist diabetes team. Most people feel very anxious when they find out they need to start taking insulin. But when you are starting on insulin you will get lots of help and support. Your insulin therapy can be tailored to fit with your own particular lifestyle.

Insulin injections go just under your skin and not into a vein. Insulin has to be taken by injection, because if it is taken as a tablet, it gets broken down in your gut and ceases to be insulin. In some countries, research has been done into giving insulin in an inhaled form (similar to an asthma inhaler). This has been somewhat successful, but there are still problems with this system and it is not widely available commercially.

More energy on insulin
People often feel much better and more energetic once they get established on insulin. They have often been short of their own insulin for a long time and this has made them feel unwell, tired, and often prone to all sorts of infections.

Where does the insulin come from?

The insulin you get from the chemist is called 'human insulin'. Many years ago insulin for injection came from pigs or cows and was called 'porcine insulin' or 'bovine insulin'.

Human insulin is manufactured in the laboratory. It is made by cell organisms that have had the human gene for making insulin spliced into them. These cells then busily make insulin. This human insulin is a very safe product to take and there have been no instances of insulin becoming contaminated with anything harmful.

Injected insulin: basic principles

The timing and the type of insulin you take is usually based around two principles:

• your body needs and uses insulin in several different ways
• when you take insulin by injection it is important to try to mimic, as closely as possible, the way your body would naturally release insulin.

Your body needs a constant low level of insulin all the time. It also needs spurts of extra insulin when you eat, to help process the glucose you get from food. 

Basal insulin

The low level of insulin your body needs all the time is called 'basal insulin' or 'background insulin'. This constant low level of insulin keeps several body processes in balance. One of these processes relates to your liver. Your liver is an organ that is able to make extra glucose to release into your bloodstream. It does this when it is 'told' to do so.

The two main things that tell your liver to make extra glucose are either:

• when your level of insulin gets very low; or
• when your level of stress hormones gets high.

Keeping liver process in check
So, one of the main things your basal insulin does, is to stop your liver making too much glucose. If you think of your liver as a potential glucose factory, you can think of your basal insulin as keeping a lid on that factory.

If you don't have enough basal insulin, the lid gets loose and extra glucose starts escaping from your liver into your bloodstream. And so your blood glucose levels start to get too high. This is why your blood glucose levels can go up overnight even if you have not eaten anything (because of your liver making glucose). Also see: High blood glucose type 1 diabetes

On the other hand, if you have too much basal insulin, it can cause your blood glucose level to go too low. This is because it dampens down your liver's ability to make glucose by too much. It also causes your blood glucose to be moved out into your cells and muscles and be burnt up too quickly. Also see: Low blood glucose type 1 diabetes

In practice this means that managing your basal insulin at the right level is a balancing act.

Intermediate and long-acting insulins

Insulin by injection comes in different types. These types are defined by their length of action in the body (the length of time they remain in your body). 'Intermediate' or 'long' acting insulins are normally used to give your body its basal supply of insulin. The majority of people use intermediate-acting insulin for a basal level of insulin.

Intermediate-acting insulin is used for basal needs because it is absorbed slowly over a 24-hour period. It does have a 'peak' absorption period, however.

For basal insulin requirements, some people take a single daily dose of intermediate insulin, while others take intermediate-acting insulin twice a day (about 12 hours apart).

The only exception to using intermediate or long-acting insulin for basal insulin is if you use an insulin pump. The way an insulin pump works means it delivers very tiny but constant amounts of insulin, so it uses short or very-short-acting insulin, which acts as basal insulin in this instance.

Spurts of insulin ('bolus' insulin)

Your body needs basal insulin to help maintain a steady blood glucose level, not too high or too low. But it also needs spurts of insulin (or 'boluses' of insulin) to give you extra insulin on top of your basal insulin when you need it.

When do you need spurts of insulin?

You need spurts of insuin when you eat. When you eat carbohydrate food your body converts the carbohydrate into glucose and absorbs it into your bloodstream. You need extra insulin to process this extra blood glucose. The processing of this glucose means either moving it into your body cells to get burnt as energy or moving it into your body cells to be stored as extra glucose for when you need it (eg. for when you are exercising).

Stored glucose is called 'glycogen'. Your extra spurts of insulin perform both these tasks; enabling glucose to be both stored and used.

The insulin you use to give your body the extra spurts of insulin when you eat is either short-acting insulin or very-short-acting insulin.

Short-acting insulin

Short-acting insulin has an absorption profile that extends slightly beyond the blood glucose profile that your body has after it eats a meal. Because of this, if you are using short-acting insulin for your meals, you generally need to eat a small snack 2 - 3 hours after the meal. This is to provide enough glucose for the tail end of your short-acting insulin to work on.

Short-acting insulin also acts best if you take it 15 - 20 minutes before you eat, as it takes this long to start being absorbed. It has a better chance of matching your post-meal blood glucose profile if you give it a head start.

Very short-acting insulin

Very short-acting insulin is also used to give you spurts of insulin for processing the glucose you get from food. Very short-acting insulin wears off sooner than short-acting insulin. This means you usually don't need to have an extra snack after your meal to cover the action of very short-acting insulin. It is also absorbed much more quickly than short-acting insulin. So, instead of needing to take it 20 minutes before food, you can take it with your food (or even immediately after food).

What types of insulin are currently available in New Zealand?

The insulins available are divided into four main types. These are defined by how long the insulin takes to be absorbed into your bloodstream from under your skin, and how long it continues to act in your body.

The four types are:

• very short-acting insulin (eg, Humalog, NovoRapid)
• short-acting insulin (eg, Actrapid, Humulin R)
• intermediate-acting insulin (eg, Protaphane, HumulinNPH)
• long-acting insulin (eg, Lantus).

Some of the above insulins are available in pre-made mixtures, where an intermediate-acting insulin is mixed with a short-acting insulin.

These premixes come in varying combinations, or ratios, between the short and intermediate insulin. The premixes are always labelled by how much of the mixture is short-acting insulin. For example, a mix called 'Mixtard 30' will have 30% short-acting insulin and 70% intermediate-acting insulin. A mix called 'Penmix 50' will contain 50% short-acting insulin and 50% intermediate-acting insulin.

What determines what type of insulin I take, and the times I take it?

A number of factors will determine this. These factors are likely to be:

Whether you are newly diagnosed with type 1 diabetes. Many diabetes services have preferred ways of helping people get started on insulin. Some prefer to help you start on a once or twice daily dose of intermediate-acting insulin only. Others prefer to immediately help you onto what is called a more 'intensive' way of taking insulin, that is, a four times daily dose using a combination of both short and intermediate-acting insulin.

Whether you are in the 'honeymoon phase' of your diabetes. For a period after you first start on insulin you may have very low requirements for injected insulin, because your pancreas will still be making some insulin (the 'honeymoon phase'). But the natural process of type 1 diabetes means that eventually you will need to take more insulin by injection.

What your blood glucose profile is (ie. the pattern of how your blood glucose levels vary during the day). The times of the day that your blood glucose levels are highest or lowest will influence the type of insulin your health professional will recommend to you.

Your lifestyle needs. As you become established on insulin you will work closely with your diabetes team to get onto a way of taking insulin, and using types of insulin, that best allow you to have the sort of lifestyle you want.

Your budget. Taking insulin by pump is usually an expensive option in New Zealand.

Insulin devices

There are several devices available to deliver insulin. These include:

• disposable insulin syringes
• insulin pens
• insulin pumps
• auto-injector devices (may not be recommended in the long term).

Disposable insulin syringe

There are a number of different insulin syringes available. The length and fineness of the needles on insulin syringes (or the pen needles for pen injectors) varies also.

Needle length and gauge
The length varies from 5mm to 12.7mm. Generally if you are overweight a longer syringe needle will be best (remember even the longest syringe needle is still very short!). The fineness varies from 29 gauge to 31 gauge. These are both extremely fine gauge needles. The higher the gauge number, the finer the needle.

Mixing doses
Syringes are useful for people who need to mix two different sorts of insulin into the same syringe. Mixing this dose into one syringe allows them to have one injection at this time instead of two.

A lot of young children have their insulin by syringe. This is because they are often taking their insulin twice a day (to avoid having to take insulin at lunch time when at school), and the dose is often a mix of intermediate- and short-acting insulin. So insulin syringes work very well for them.

You can get 100 funded syringes on a prescription, if your doctor prescribes these at the same time as your insulin, and they will be issued by your pharmacy. You can also purchase extra syringes either from your pharmacy or from Diabetes New Zealand shop.

Insulin pens

Insulin pens are devices that look similar to a rather heavy-duty fountain or ink pen. You load them with a cartridge of insulin and they have a short needle on the end of them (covered by their lid except when in use) that allows you to use them to inject your insulin.

Many people like pens because they are a very discreet way to take your insulin. When using a pen it is possible to take your insulin in a crowded room and for no one to notice you have done so.

Some premixed insulins (mixtures of short-acting and intermediate-acting insulin) come in cartridges that can be fitted into an insulin pen.

Auto-injector devices

Auto-injector devices (such as Pen Mate or Inject-Ease) are designed to be loaded with either an insulin pen or an insulin syringe.

Once loaded, the devices have a button that automatically fires the needle into your skin. Some people who are very anxious about needles find these devices helpful (young children, for example).

However, they are quite bulky and if you are able to use an insulin pen or a syringe direct it is usually much easier long-term if you do so.

Insulin pumps

Insulin pumps are small devices that are worn externally, often on a belt clip. They weigh about 100 grams and look very much like a pager. Pumps are battery powered and can be programmed to deliver a stream of rapid-acting insulin in frequent tiny doses, while additional doses can be delivered at meal times.

You load them with a syringe full of either short-acting, or very short-acting insulin. This syringe is connected to a length of fine plastic tubing which goes into a very fine cannula (or plastic needle) secured under your skin. When you are on a pump you change this cannula about every 2 - 3 days.

Insulin pumps cost around $5000 to $8000. There is an additional cost for the consumables (cannulas, infusion set, batteries, cartridge refilling devices) needed and this is around $2000 to $2500 each year. Currently, insulin pumps are not subsidised in New Zealand, so most people would have to cover the costs themselves. However, the Ministry of Health does provide some insulin pumps free of cost.

If you think a pump would be good for you, talk with your diabetes specialist and nurse educator about the criteria you need to meet to qualify for a free pump.

Insulin regimens

For information on insulin regimens, refer to Diabetes New Zealand (contact details further below).

Related topics

Also see: Laboratory tests for diabetes

Original material provided by Diabetes New Zealand, 2008. Edited by everybody, August 2011.