Dr Gill Jenkins last medically reviewed this article in May 2020.
Causes of type 1 diabetes
In type 1 diabetes, the cells in the pancreas that make insulin are destroyed, causing a severe lack of insulin. This is usually thought to be the result of the body attacking and destroying its own cells in the pancreas, known as an autoimmune reaction.
It isn’t clear why this happens, but a number of explanations and possible triggers have been proposed. These include:
- Infection with a specific virus or bacteria
- Exposure to food-borne chemical toxins
- Exposure as a very young infant to cow’s milk, where an as yet unidentified component triggers the autoimmune reaction
However, these are only hypotheses and are not proven causes.
As with other autoimmune diseases, an underlying genetic disposition seems to play a part, leaving some people more vulnerable to these triggers.
In rare cases, damage to the pancreas by tumours, toxins or injury (including surgery), can also lead to type 1 diabetes.
Development of type 2 diabetes is usually multifactorial – that is, several factors combine to cause it. The most important of these is genetics. Children of people with type 2 diabetes have a one in three chance of developing the condition themselves.
In this type of diabetes, the receptors on cells in the body that normally respond to the action of insulin fail to be stimulated by it. This is known as insulin resistance.
In response to this, more insulin may be produced and this overproduction exhausts the insulin-manufacturing cells in the pancreas. There is simply insufficient insulin available and the insulin that is available may be abnormal and so doesn’t work properly.
The following risk factors increase the chances of someone developing type 2 diabetes:
- Increasing age
- Physical inactivity
Rarer causes of type 2 diabetes include:
- Certain medicines
- Pregnancy (gestational diabetes)
- Any illness or disease that damages the pancreas and affects its ability to produce insulin, such as pancreatitis
It’s important to be aware of myths about the causes of diabetes. Eating too much sugar does not cause diabetes. However, it may cause obesity and this is associated with people developing type 2 diabetes.
Stress alone does not cause diabetes, although it may be a trigger for autoimmune disease as in type 1 diabetes. There is also evidence that chronic stress increases the risk of the development of a complex condition known as metabolic syndrome. Metabolic syndrome includes features such as abdominal obesity, abnormal blood fat levels , high blood pressure and insulin resistance, which increases the risk of type 2 diabetes.
Stress can also make the symptoms worse for people who already have diabetes and make control of their diabetes difficult.
Diabetes is not contagious, so someone with diabetes can’t pass it on to anyone else.
Type 1 diabetes treatments
Type 1 diabetes is treated with insulin and by eating a healthy diet. Insulin can’t be taken by mouth because the digestive juices in the stomach destroy it. This means that for most people it has to be given by injections. Most people find giving the injections simple and relatively painless, since the needle is so fine.
How often someone needs to inject depends on what their diabetes specialist has recommended, and which type of insulin they’re using. Insulin is given at regular intervals throughout the day, usually two to four times.
Each injection may contain one, or a combination of different types of insulin, which act for a short, intermediate or longer period of time.
Injections can be given using either a traditional needle and plastic syringe, or with an injection pen device, which many people find more convenient.
An automatic insulin pump is available, which means that fewer injections are needed. The needle is sited under the skin, and connected to a small electrical pump that attaches to a belt or waistband and is about the size of a pager. Inside is a reservoir of fast-acting insulin which is delivered continuously at an adjustable rate.
Inhaled insulin recently became available for treating people with a proven needle phobia or people who have severe trouble injecting. It was hoped that this would become a mainstay method of giving insulin, but initial results were not as impressive as hoped, and so this option is now usually reserved for those patients where all other treatment options have failed.
Insulin was first used to treat diabetes in 1921. Under normal circumstances, it’s made by beta cells that are part of a cluster of hormone-producing cells in the pancreas.
The hormone regulates the level of glucose in the blood, preventing the level from going too high. Insulin enables cells to take up the amount of glucose they need to provide themselves with enough energy to function properly. It also allows any glucose left over to be stored in the liver.
Most insulin used today is human insulin, although some people still use insulin from cows and pigs. Human insulin is a product of genetic engineering, where bacteria bred in a laboratory are given a gene that allows them to produce insulin. Analogue insulin is another form of artificially modified insulin.
There are six main types of insulin, and each patient requires their own unique combination and dosage. It can take many weeks after starting insulin for sugar levels to stabilise, and it is quite common for different insulin combinations to be tried before optimal treatment occurs. The six types are:
- Rapid-acting analogue insulins – as the name suggests, these act quickly and are used up within five hours. A clear-looking insulin, these injections are taken with food
- Short-acting insulin – a clear insulin, this is injected around half an hour before a meal, and last for up to eight hours
- Longer-acting analogue insulin – used increasingly in many diabetics, these are given once daily only to provide a background insulin cover for 24 hours. A clear insulin that does not need to be taken with food but, is given at the same time each day (this time varies between patients)
- Medium/long-acting insulin – usually given in combination with shorter-acting insulins, these are injected up to twice a day. Their effect can last over 24 hours
- Mixed analogue – this artificial insulin is a combination of rapid acting analogue and medium insulin. Depending on the combination used its effect can last over 12 hours
- Mixed insulin – a simple combination of short and medium acting insulins. Its length of action is similar to that of the mixed analogues
Another recent treatment, known as Exenatide, is also given by injection, but is not an insulin. Given twice daily before morning and evening meals, it works by increasing the levels of body hormones known as ‘incretins’. These are set to play an increasing role in our management and understanding of diabetes as they help to produce insulin when required, reduce appetite, slow down food absorption, and reduce glucose production by the liver. This treatment is usually only initiated by a diabetes consultant rather than a GP.
Type 2 diabetes may have been considered the milder form of diabetes in the past, but this is no longer the case. For many people, type 2 diabetes can be controlled by diet alone. Medication in tablet form is used when diet doesn’t provide adequate control.
The different types of tablets work by one of these methods:
- Helping the pancreas to make more insulin
- Increasing the use of glucose and decreasing glucose production
- Slowing down the absorption of glucose from the intestine
- Stimulating insulin release from the pancreas
- Enabling the body to use its natural insulin more effectively
Examples of these tablets include:
- Biguanides (eg Metformin) – these cut down production of glucose by the liver and help insulin carry glucose into muscles more effectively
- Sulphonylureas (eg Gliclazide) – these stimulate pancreas cells to produce more insulin as well as helping insulin work effectively in the body
- Glitazones (eg Rosiglitazone) – taken up to twice a day these tablets allow the insulin that the body produces naturally to work more efficiently
- Prandial glucose regulators (eg Repaglinide) – these aren’t usually a first line treatment of diabetes but work by stimulating the pancreas to produce more insulin. Fast-working, their effect lasts only a short time
- DPP-4 inhibitors (gliptins) – a newer treatment, which blocks the action of the DPP-4 enzyme that destroys the hormone incretin. This hormone helps the body produce more insulin as well as cutting down the amount of glucose produced by the liver
- Alpha glucosidase inhibitors (eg Acarbose) – this works by slowing down the rise in blood glucose after eating
All tablets used in the treatment of diabetes have potential side effects such as abdominal pains, diarrhoea and low blood sugar (hypos), but the majority of patients taking them are able to find one or more that suits them.
Over time, a careful diet combined with oral medication may not be sufficient to keep the diabetes under control. If this is the case then insulin injections may be recommended.