'By the 1970s, it had become clear that there are two distinct types of diabetes'

Types of diabetes

By the 1970s, it had become clear that there are two distinct types of diabetes:

1. Type 1 diabetes usually first occurs in children or young adults. It comes on quite suddenly with marked symptoms such as thirst and weight loss, and can only be treated with insulin.

2. Type 2 diabetes usually occurs in later life, and it has become increasingly clear that it is related to increasing weight gain, as a result of excess food intake and/or too little exercise. Its onset is often much more gradual without causing any specific symptoms, and it is sometimes diagnosed by a screening blood test. Type 2 diabetes can be controlled by lifestyle changes, principally by modifying diet. Many people are prescribed drugs to control type 2 diabetes, and until relatively recently it was thought that most people would eventually need insulin.

Since then our understanding has developed further, inasmuch as there are rare forms of diabetes that occur in young people (so called maturity-onset diabetes of the young or MODY). These are inherited conditions, are not associated with weight gain, and there is usually a strong family history of diabetes. Although they usually present in childhood, most cases can be controlled with tablets rather than insulin.

It has also become apparent that the distinction between type 1 and type 2 diabetes is not as clear cut as previously thought, and for those who are diagnosed in the forties and fifties, there may be a period of uncertainty before one can definitely distinguish between the two. For example, some overweight adults present quite acutely with very high glucose levels and require insulin at diagnosis, but can later be switched to tablets. Conversely, there is a type of type 1 diabetes that occurs in older people, sometimes referred to as latent autoimmune diabetes of adulthood (LADA). Like type 1 diabetes, people with this condition are not overweight; however, the onset is more like type 2 diabetes, and they may be treated with tablets for a period. Within a few years, it becomes clear they need insulin, and from that time behave very much like type 1 diabetes.

Gestational diabetes is a condition in which diabetes occurs during pregnancy. It is similar to type 2 diabetes and can be controlled with diet in some cases, otherwise insulin is used, as tablets are generally not advised in pregnancy. It usually reverses once the baby is born, but both the mother and the child are at increased risk of developing type 2 diabetes in later life.

Diabetes can also arise as a result of other diseases affecting hormones (e.g. acromegaly, caused by too much growth hormone, or Cushing’s disease, caused by too much cortisol). These cases generally reverse once the underlying condition has been treated. Cortisol is the body’s natural steroid, and people who have been treated with steroids for long periods of time for conditions such as asthma may develop diabetes. Diabetes also occurs if the pancreas is affected by other diseases, or if the pancreas has been wholly or partly removed.