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SOME QUESTIONS AND ANSWERS
What causes diabetes?
Type 1 diabetes is thought to be an
autoimmune disease, in which the body's immune
system attacks and destroys the beta cells in the
pancreas that make insulin. It is not known exactly
what triggers this immune attack, but susceptibility
to the disease is inherited.
Type 1 diabetes usually appears in the first three
decades of life and may develop quickly. It has
evident symptoms and is life-threatening if not
treated. The isolation of insulin by Banting and
Best more than 80 years ago greatly improved the
outlook for those with type 1 diabetes. Injecting
insulin is still the main treatment for diabetes.
Type 2 diabetes typically emerges in middle or
later life and has different causes from type 1.
Growing resistance to the action of insulin, often
related to the development of obesity, and an
eventual failure of insulin-producing beta-cells in
the pancreas underlie type 2 diabetes. At first, as
blood glucose levels rise, the pancreas adjusts by
increasing its output of insulin to compensate for
this rise in glucose. Eventually, however, damage
to the beta-cells causes a drop in insulin
production and a further rise in blood glucose. For
a long time, there may not be any clear symptoms,
and it is thought that there may be a million or
more people in the United Kingdom in whom the
disease is present but not yet diagnosed. Because
of this stealthy and silent onset, many people with
type 2 diabetes already have detectable signs of
one or more of the longer-term complications by
the time the disease is diagnosed.
Susceptibility to type 2 diabetes is also known to
be inherited, but this aspect is complex and little
understood. A person's lifestyle has a major
influence on whether or not they develop the
disease, and how quickly. Making changes to
these habits is a vital part of preventing and
managing the disease. Type 2 diabetes is much
more common than type 1 diabetes and accounts
for about 90 per cent of all diagnosed cases of
diabetes in the United Kingdom.
Gestational diabetes is said to be present
when glucose intolerance, resulting from the
development of insulin resistance, first emerges in
pregnancy. This mainly occurs in the second or
third trimester and affects about 2-5 per cent of
pregnancies. Pregnancy affects blood glucose
levels in many women (with the needs of the foetus
tending to lower blood sugar levels), but in some
mothers, blood sugar instead increases to the point
where it is considered to indicate gestational
diabetes.
Secretion of hormones from the placenta is a
major cause of the insulin resistance. Following
birth, when these hormone levels drop, blood
glucose levels usually return to normal, but women
who have experienced gestational diabetes have
an approximately 30 per cent lifetime risk of
subsequently developing type 2 diabetes.
Who gets diabetes?
In the United Kingdom, half of all people who
eventually develop type 1 diabetes are
diagnosed under the age of 15; 90 per cent have
been diagnosed by the age of 30.
There is a large variation in the frequency of
diagnosis of new cases per year between different
countries. The figure is as high as 49 cases per
100,000 people per year in children up to the age of 14 in Finland and 32 per 100,000 per
year in Sweden, through rates of 15 to 20 per
100,000 per year in the United Kingdom, to fewer
than 5 per 100,000 people per year in many
parts of South America and China. There may also
be marked differences between different areas of
the same country.
This suggests that both inherited and environmental
factors may influence the onset of diabetes. Long term
immigrants from a country with a low
incidence rate who move to one with a high rate
tend to show an increased incidence of the
condition, approaching that in their adopted
country.
Type 2 diabetes also varies in frequency from
place to place. The highest rates are found in
some US indigenous peoples (e.g. Pima Indians in
Arizona) and in various South Pacific islands, but
are generally low in low-income, rural
communities, rising with development level and
urbanisation. India and China are the countries
with the largest number of diagnosed cases of type
2 diabetes.
In the United Kingdom, type 2 diabetes accounts
for 85-90 per cent of all diagnosed cases of
diabetes and prevalence increases markedly with
age. Over the age of 35, prevalence is higher in
men than in women. UK-based surveys have
shown that the disease is more common in black
Caribbean and especially South Asian (Indian,
Pakistani, Bangladeshi) communities than in the
white population.
Accurate statistics are not available for
gestational diabetes, as there is no agreed
standard definition. However, it is more likely to
be seen in women who:
- are obese
- have a family history of type 2 diabetes
- have had an unusually large baby in a
previous pregnancy
- had an unexplained stillbirth or neonatal death
- belong to an ethnic group with an increased
risk for type 2 diabetes.
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