5.3 Type 2 diabetes
Type 2 diabetes was previously called non insulin-dependent diabetes. People with Type 2 diabetes produce insulin but it may be in insufficient amounts and/or their cells are resistant to the action of insulin (Figure 7). Hyperglycaemic symptoms, such as thirst and passing large amounts of urine, may be absent. Ketoacidosis does not usually develop as there is sufficient insulin to prevent it.
Type 2 diabetes may be present for many years before a diagnosis is made. This is because some people may have few symptoms. Others do not see their thirst or getting up at night to pass urine as a problem. Having diabetes for several years before a diagnosis is made can mean that complications of diabetes, which take years to develop, may already be present at the time of diagnosis. This is one of the reasons why Diabetes UK, the diabetes charity, tries to raise awareness of diabetes and supports screening programmes for this condition.
Genes are thought to be important in the development of Type 2 diabetes. In a very rare form of Type 2 diabetes, definite gene defects have been identified. This condition is called maturity onset diabetes of the young (MODY), as it usually occurs before the age of 25 years. Thus in a family with a very strong family history of diabetes occurring before the age of 25 years this diagnosis needs to be considered. Furthermore, certain population groups, for example Asian and African–Caribbean people, are at an increased risk of developing Type 2 diabetes.
Other factors are also important. Obesity and lack of exercise are two particularly important environmental factors thought to be contributing to the rapidly increasing numbers of people worldwide with Type 2 diabetes (Section 6.3). Although Type 2 diabetes has usually been considered to be a condition of adults, particularly those over 40 years old, it is occurring with increasing frequency in adolescents.
The amount of insulin that is produced in someone with Type 2 diabetes often decreases over a period of years, although in some people there is a faster decline. In many people the condition is progressive, and eventually, to maintain the correct glucose level with the aim of preventing symptoms and decreasing the risk of complications, insulin is often required. Some people may in fact have slowly developing Type 1 diabetes. Thus treatment of Type 2 diabetes often starts with improvements to diet, i.e. changes in the amounts and types of food, and an increase in physical activity, progressing to tablets and then onto insulin. More tablets are added if required.
All diabetes is equally important. A person with Type 2 diabetes who is being treated with modifications to diet alone can develop as many complications as someone with Type 1 diabetes who is being treated with insulin, because diabetes impairs fundamental physiological processes, energy supply to cells, and the composition of the blood.
Although it may seem quite clear cut, in reality it can be difficult to decide whether a patient has Type 1 or Type 2 diabetes; for example, knowing that someone is on insulin therapy cannot be used to distinguish whether they have Type 1 or Type 2 diabetes. This is illustrated in Activity 5.
Activity 5: The differences between Type 1 and Type 2 diabetes
Take a few minutes to quickly re-read the last two sections on Type 1 and Type 2 diabetes and make a list of the differences between the two types. If you have diabetes list the reasons why you fit into one category or another. If you do not have diabetes but know someone who does, try asking them if they would mind if you tried to work out which type of diabetes they had. Are you right?
If your work involves people with diabetes identify two or three of them and try to decide whether they have Type 1 or Type 2 diabetes.
If you kept your notes from Activity 1, now would be a good time to reflect on them to see if your understanding has changed.
Case study 5 introduces you to John. As you read it make notes on the clues that indicate that John has Type 2 diabetes.
Case study 5
John is 30 years old. He is married with two children and is buying his first house. He works as a long-distance lorry driver. He has always been overweight and currently weighs 120 kg. The demands of his job leave little time for exercise. He needs life insurance and his insurers have asked him to have a medical to assess his risk. He sees his GP for the first time in years. He provides a urine sample that shows a large amount of glucose but no ketones. His blood pressure is high, measuring 160/110 mmHg. He does not smoke. A high random glucose test of 13 mmol/l is confirmed by the fasting laboratory blood tests showing a plasma glucose level of 9 mmol/l and a cholesterol level of 8 mmol/l (a high value; ideally it should be about 5 mmol/l).
Sometimes it can be very easy to tell if someone has Type 1 or Type 2 diabetes. For example, someone on tablets only who has had diabetes for several years has Type 2 diabetes. Someone who comes to hospital or a doctor's surgery with loss of weight and presence of ketones and immediately starts insulin treatment has Type 1 diabetes.
However, it is not always so simple. Someone who has lost only a small amount of weight, and whose plasma glucose level cannot be controlled with tablets and remains high after several weeks of trying to reduce it, may in fact be developing Type 1 diabetes. You would need to have asked the right questions to find out if they had Type 1 or Type 2 diabetes. More and more people with Type 2 diabetes progress to taking insulin injections as well as their tablets as time goes by. They still have Type 2 diabetes but need insulin to control their blood glucose levels.
John fits the bill as the sort of person who would be at risk of developing Type 2 diabetes: he is overweight and takes no exercise. It would be interesting to know his family history, to determine if there is any genetic influence. The high level of glucose in his urine and random blood test is confirmed by his fasting blood glucose level of 9 mmol/l, indicating a diagnosis of diabetes. Without symptoms, two abnormal glucose levels are required. John's lack of symptoms and the absence of ketones make one think that he has Type 2 diabetes rather than Type 1.