Insulin is an essential hormone. Without it, the body cannot control or properly use glucose (sugar) – one of its main energy supplying fuels.
How does insulin help diabetes?
People with Type 1 diabetes produce inadequate amounts of insulin, so insulin replacement is their key treatment.
Without adequate insulin replacement, people with Type 1 diabetes will see their blood sugar levels rise and the body will start to burn up its fat stores. In a few days this leads to a condition called diabetic acidosis, which is life threatening.
Too much insulin, on the other hand, leads to such low levels of blood sugar that it causes a condition called hypoglycaemia.
The symptoms include paleness, shaking, shivering, perspiration, rapid heartbeat, hunger, anxiety and blurred vision. In some cases it can cause loss of consciousness (hypoglycaemic coma) and convulsions.
In Type 2 diabetes the problem is not a lack of insulin output, but increasing resistance of your cells to the effects of insulin.
In the early years, the body compensates for this insulin resistance by increasing the output of insulin from the pancreas gland.
Ultimately, the pancreas becomes unable to cope.
About 25 per cent of people with Type 2 diabetes eventually need treatment with insulin. The longer a person has Type 2 diabetes, the more likely they will have to start insulin treatment at some point.
There are four main kinds of injectable insulin.
Short-acting insulin: soluble insulin (eg Actrapid, Humulin S, Hypurin bovine neutral, Hypurin porcine neutral, Insuman rapid, Pork actrapid, Velosulin) starts working within 30 to 60 minutes and lasts six to eight hours. The insulin analogues insulin aspart (NovoRapid), insulin lispro (Humalog) and insulin glulisine (Apidra) start working within 15 minutes and last for up to five hours.
Intermediate-acting insulin: isophane insulin (eg Humulin I, Hypurin bovine isophane, Hypurin porcine isophane, Insulatard, Insuman basal, Pork insulatard) starts working after one to two hours and lasts 10 to 14 hours.
Long-acting insulin: insulin zinc suspension (Hypurin bovine lente), protamine zinc insulin (Hypurin bovine protamine zinc), and the insulin analogues insulin glargine (Lantus) and insulin detemir (Levemir). They start working after one to two hours and last for up to 24 hours.
Biphasic insulins: mixtures of short-acting and intermediate-acting insulins in different proportions, such as 30/70, 50/50 (eg NovoMix 30, Humulin M3, Hypurin porcine 30/70, Insuman comb, Mixtard, Pork mixtard 30, Humalog Mix25). The type of insulin you use will depend on your individual needs and lifestyle.
An inhaled insulin product (Exubera) was launched in the UK in August 2006. It is a short acting insulin that starts working within 10 to 20 minutes and lasts for around six hours.
How often do I take insulin?
There are three common insulin regimes.
1. Twice daily doses of short- and intermediate-acting insulin
These are given before breakfast and before the evening meal.
The short-acting doses cover the insulin needs of the morning and evening.
The intermediate-acting doses cover the afternoon and overnight.
The pre-mixed insulin injections are convenient for this type of dosing.
2. Three times a day dosing
Short-acting and intermediate-acting insulin before breakfast.
Short-acting insulin before the evening meal.
Intermediate-acting insulin before bed.
Moving the second intermediate-acting dose to before bedtime gives better coverage of the overnight period.
3. Multiple daily doses
Short-acting insulin is used before each main meal.
An intermediate or long-acting insulin is used before bedtime to give coverage overnight.
How is insulin taken?
Most people use insulin in:
disposable insulin pens cartridges that go in multiple-use insulin pens.
Needles for pens are disposable and come in 5mm, 6mm, 8mm, 10mm, 12mm and 12.7mm lengths.
Your diabetes specialist will advise on which is most suitable for you.
A new needle should be used for each injection.
Exubera is a new powdered form of insulin that is inhaled into the lungs from an insulin inhaler, similar to those used for asthma.
There are other types of regimes - for example diabetes in some older people can be adequately controlled with a single daily injection of long-acting insulin.
Pump treatment is sometimes used in young people with diabetes. It involves a constant drip-feed of insulin through a needle in the skin and extra insulin doses with meals. The feed is controlled by a small portable pump called an infusion pump.
Multiple injections are increasingly being favoured, because they give the most flexibility and are most capable of mimicking natural insulin release.
The regimen needed and the dose used will be adjusted on an individual basis until you and your doctor find the combination that controls your blood sugar best.
Insulin is inactivated by the digestive enzymes in the gut and can't be taken by mouth. Insulin is therefore most commonly given as an injection under the skin (subcutaneously), usually into the thigh, buttocks, abdomen or upper arm.
The needles used are very small. Although the injections can be a little painful at first, people soon get used to them and they become second nature.
A member of your diabetes team will teach you how to inject yourself. If you have any concerns or questions about your insulin injection, these are the people to ask for help.
You should use:
short-acting insulin injected in the skin of your abdomen
intermediate- or long-acting insulin injected in the thigh
insulin mix can be injected in either place.
To inject, take a small fold of skin between the fingers, insert the needle at an angle and inject the right amount of insulin. Then slowly retract the needle and let go of the fold of skin. With short needles you don't need to pick up a fold of skin to inject into.
Rotate the injection site you use on a regular basis, because overusing one site can cause the fatty tissue there to thicken. This is called lipodystrophy and can lead to erratic absorption of the insulin from that site.
Exercising after an injection can increase the speed that the insulin is absorbed into your bloodstream.
There is no doubt that the launch of inhaled insulin this year (2006) is a breakthrough in the treatment of diabetes. However, it will not be suitable for all people with diabetes and how popular it will become remains to be seen.
This is because the only type of insulin that can be delivered in this way at the moment is a short-acting type. This means that most people with type one diabetes will still need to use injections to administer their intermediate or long-acting insulin.
The inhaled insulin can't be use by people who smoke, or who have lung diseases like asthma or COPD.
There are also still some concerns over the long-term effects on the lungs of inhaling insulin.
The National Institute for Health and Clinical Excellence (NICE) are still reviewing their recommendations on who should use inhaled insulin. At the moment, their draft guidance recommends that it should only be used by people who have a genuine needle phobia diagnosed by a psychiatrist or psychologist, or who have severe persistent problems with injection sites.
What can I do myself?
Learn the proper way to inject yourself from the start.
Your specialist diabetes nurse may also want to lower your blood sugar level to a hypoglycaemic range on purpose. This way you will know:
the warning symptoms of a hypoglycaemic reaction
how to get your blood glucose level up again.
Measure your blood sugar every day to learn how to react to eating, exercise and changes in insulin dosage. This is the only way to get a good feel for, and control of, blood glucose levels.
Initially your doctor can help you adjust the insulin dose to suit your lifestyle. Later you will know enough about your condition to do this alone.
How do I know when to adjust insulin?
Good blood sugar control is essential.
But the harder you try to keep blood sugar low, the greater the risk of a hypoglycaemic attack.
You need to strike a balance between strict glucose control and the need to avoid hypos.
More short-acting insulin is usually needed when:
eating more than usual
doing less physical activity, eg taking the car to work instead of riding a bike.
Less short-acting insulin is needed when:
eating less doing more physical activity.
The dose of long-acting insulin should not be adjusted as a short-term measure - for example if the blood sugar level is high on one occasion only.
This is because a change in dose doesn't change the body's glucose levels immediately and can affect sugar levels in the next few days.
Targets for insulin treatment
The aims of treating diabetes are not the same for everyone.
In a young or middle-aged person with a long life expectancy, good control of the diabetes will reduce the risk of long-term complications developing. But this will require fairly intensive monitoring and adjustment of the diabetes.
Good control in Type 1 diabetes would be blood glucose consistently between 4mmol/l and 7mmol/l.
This should result in a HbA1c level (long-term glucose level) of 7 per cent or less.
In an elderly person or someone with a limited outlook for other medical reasons, it may be inappropriate to be so precise with insulin treatment.
Instead, controlling diabetes symptoms by reducing blood sugar levels may be all that's required.
Less strict control, so blood glucose is around 10 mmol/l, may be good enough to stop symptoms such as thirst and the frequent desire to pass urine.