13 June 2018

What is type 1 diabetes?

A history of diabetes

The full name of the condition is diabetes mellitus, which literally means ‘passing [perhaps more accurately “pissing”] honey’, as in diabetes the urine contains glucose and so tastes sweet. Diabetes was described in ancient Egypt, in the Papyrus Ebers, which dates from around 1500BC, as a disease where urine is too plentiful. Sushruta of the Hindus wrote in 1000BC that the urine was sweet and that ants and flies were attracted to it. He thought that diabetes was a disease of the urinary tract (kidneys and bladder) and wrote that it could be inherited or develop as a result of dietary excess or obesity (perhaps referring to type 1 and type 2 diabetes). The recommended treatment was exercise. It was not until the seventeenth century that it was discovered that the urine was sweet because it contained sugar and that diabetes was a disease of the pancreas rather than the kidneys. This was established in 1682 by Johann Brunner, who removed the pancreas from dogs and found this led to diabetes. In 1797, John Rollo, the surgeon-general of the Royal Artillery, wrote a book in which he described the case of a Captain Meredith, who took a diet low in carbohydrate and high in fat and protein. His weight fell from 105kg to 73kg (or 230 to 160lb) and the symptoms resolved. At that stage diabetes was reported as being relatively rare, and associated with wealth.

It was not until the end of the nineteenth century that the role of insulin became apparent. In 1889 Mehring and Minkowski removed the pancreas from dogs to cause diabetes. This was then reversed by transplantation of small pieces back into the peritoneum (the lining of the abdominal cavity). In 1921 Banting and Best isolated an extract of pancreatic islet cells and found this reduced glucose levels in diabetic dogs. The following year, this extract (a prototype of insulin) was injected for the first time into a patient with diabetes, a 14-year-old boy called Leonard Thompson.

Piece by piece the puzzle was being completed, such that by the 1920s, it was established that diabetes is characterised by an excess of sugar (glucose) in the blood, causing excess in the urine. The disease was often seen in overweight people, in whom it could be controlled by adopting a low carbohydrate diet. In other patients, insulin, extracted from animal pancreases and given by injection, led to a fall in blood glucose levels.

Take Control of Type 1 Diabetes

'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.

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