John_Yudkin_-_Pure_White_and_Deadly_revised_1986_OCR

15
Too much
blood sugar
-or
too little
T he way the body works is largely a matter of
keeping the organs and tissues in a pretty constant environment
inside the body. Anything, for example, that makes the level of
sugar (glucose) in your blood fall below normal, or rise above normal,
is promptly followed by actions that restore it to its original
level. These actions are controlled partly by the nervous system but
chiefly by the hormones. If for any reason the control mechanisms
are not working properly, you will have an excessive amount of
sugar in the blood, or a deficient amount, for part or all of the time.
The condition of a high blood sugar is called hyperglycaemia, and
that of a low blood sugar, hypoglycaemia.
Diabetes
The commonest cause of hyperglycaemia is diabetes.
Diabetes (more strictly, diabetes mellitus) is a disease that has
been studied in very great detail for quite a long time - certainly
over 100 years. Research workers are still, however, not at all clear
about several features of the disease. In trying to summarize what
we do know, I shall inevitably have to make it sound much simpler
than it really is; I shall have also to be much more dogmatic than
the limitations of our current knowledge warrant.
Broadly speaking, diabetes occurs mostly either in children or in
middle-aged men and women. Juvenile diabetes tends to run in
families rather more than does 'maturity-onset diabetes'. Again,
when children with diabetes grow up, they are usually quite thin;
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Too much blood sugar - or too little
maturity-onset diabetes is most commonly found in overweight
people. Most patients with juvenile diabetes respond well to treatment
with insulin, while most of those with maturity-onset diabetes
are more resistant to the action of insulin. As a result, it is now
more usual to classify patients as 'insulin-dependent' or 'non-insulindependent'.
Yet another way of classifying diabetes is into Type I and
Type II. However, in practice it is quite common - especially among
non-white (non-Caucasian) patients - to find individuals who do not
clearly belong to either of these types. Soon after von Mering and Minkowski
showed in 1890 that diabetes could be produced in the dog by
the removal of its pancreas, it became evident that groups of cells in
the pancreas called the islets of Langerhans were responsible for producing
a substance that prevented diabetes. An effective preparation
of this substance was made by Banting and Best in 1921. The substance
was given the appropriate name 'insulin' (insula is the Latin
word for island).
It was natural, then, to imagine that all cases of diabetes were
caused by a failure of the islets of Langerhans to produce enough
insulin. But it is now known that this is not always true. On the
whole, such a failure is the most common cause of Type I diabetes
but not of Type II. The latter condition is often due to an insensitivity
of the cells of the body to insulin. One of the most important
actions of insulin is that of enabling the cells to utilize the glucose
from the blood which is their main source of fuel. If, however, the
cells have become insensitive to insulin, the pancreas produces more
and more insulin in order to counteract the insensitivity.
It used to be usual to treat all forms of diabetes with injections of
insulin. Nowadays, however, it is more common to treat Type II
diabetes patients with drugs by mouth. These drugs mostly fall into
two groups: those that increase insulin secretion by the pancreas,
and those that seem to increase the sensitivity of the cells to the
insulin that is already being secreted by the pancreas.
Even if their diabetes has been kept under quite good control, by
insulin injections or by oral treatment, patients are likely after several
years to develop a number of other conditions, including peripheral
vascular disease and coronary thrombosis. In addition, diabetes
can result in diseases of the eye - cataract and retinitis - and disease
of the kidney. Noone quite understands why these complications
arise, although it may be partly because of long-standing abnormal
blood-sugar levels, or because of other abnormal substances in the
blood such as 'ketone bodies'. As I shall show in Chapter 19, there
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