History
The word ‘diabetes’ comes from the Greek word for a siphon. This illustrates very clearly the main symptoms of type 1 diabetes – constant excessive drinking and passing of urine. The first written reference to diabetes dates back to 1500 bc. In 1889 Oscar Minkowski discovered that removal of the pancreas caused diabetes in animals. In 1921 Banting, Best, Collip and McLeod discovered a method of purifying insulin extracted from animals’ pancreases. The first patient to be treated with insulin received a dose in January 1922. Previously type 1 diabetes was more rapidly fatal then most cancers, and insulin was hailed as a cure for diabetes. However, by the 1930s it was clear that long-term complications became very troublesome.
Complications
High blood glucose levels for many years can damage the smallest blood vessels – capillaries. The particular tissues which are most affected by this process are the retina, nerves and kidney. These complications are known as ‘microvascular’ complications. The number of people with such complications increases as the duration of type 1 diabetes increases Large blood vessels are also affected by high blood glucose levels. These ‘macrovascular’ complications include premature heart attacks, strokes and poor circulation to the feet. Diabetes causes fat to be deposited in the arte-
rial walls, accelerating atherosclerosis (hardening of the arteries). The risk of developing these long-term complications of diabetes is directly related to how well the diabetes is controlled. It is possible to assess this by a single blood test which indicates the average blood glucose levels over a period of two months. This is possible as glucose becomes attached to the pigment in red blood cells (haemoglobin). The amount of glucose attached to haemoglobin is measured in the test as ‘HbA1c’. In non-diabetic people, the normal amount of glucose in the blood causes the level of HbA1c to be up to 6.0 per cent. A very well motivated person with type 1 diabetes may be able to achieve an HbA1c of 7.5 per cent or less. Some people can only manage to achieve HbA1c levels of over 12 per cent. A major study carried out in the US demonstrated very clearly the relationship between HbA1c and the chance of developing complications. In general, the higher the HbA1c, the higher the risk of developing complications.
A further important factor is that of blood pressure. In diabetes, the higher the blood pressure, the faster complications will develop. Very tight control of blood pressure has been shown to have a greater effect than very tight control of blood glucose in slowing the rate of progression of complications.
Although this may seem surprising at first, it has to be seen as a series of stages:
1. high blood glucose damages the capillaries and arteries
2. high blood pressure will cause the damaged capillaries to leak or burst
3. reversal of high blood pressure will have an immediate effect upon the
well-being of blood vessels
4. reversal of high blood glucose will just slow further damage
However, it has to be recognized that some people appear to be less sus-
ceptible to complications than others. Other unknown factors determine the
risk of complications for any one individual.
