Diabetes Mellitus (cont.)
What are the different types of diabetes?
There are two major types of diabetes, called type 1 and
type 2. Type 1 diabetes was also called insulin dependent diabetes mellitus
(IDDM), or juvenile onset diabetes mellitus. In type 1 diabetes, the pancreas
undergoes an autoimmune attack by the body itself, and is rendered incapable of
making insulin. Abnormal antibodies have been found in the majority of patients
with type 1 diabetes. Antibodies are proteins in the blood that are part of the
body's immune system. The patient with type 1 diabetes must rely on insulin
medication for survival.
In autoimmune diseases, such as type 1 diabetes, the
immune system mistakenly manufactures antibodies and inflammatory cells that are
directed against and cause damage to patients' own body tissues. In persons with
type 1 diabetes, the beta cells of the pancreas, which are responsible for
insulin production, are attacked by the misdirected immune system. It is
believed that the tendency to develop abnormal antibodies in type 1 diabetes is,
in part, genetically inherited, though the details are not fully understood.
Exposure to certain viral infections (mumps and
Coxsackie viruses) or other
environmental toxins may serve to trigger abnormal antibody responses that cause damage to the pancreas
cells where insulin is made. Some of the antibodies seen in type 1 diabetes include anti-islet cell antibodies, anti-insulin antibodies and anti-glutamic decarboxylase antibodies. These antibodies can be measured in the majority of
patients, and may help determine which individuals are at risk for developing
type 1 diabetes.
At present, the American Diabetes Association does not
recommend general screening of the population for type 1 diabetes, though
screening of high risk individuals, such as those with a first degree relative
(sibling or parent) with
type 1 diabetes should be encouraged. Type 1 diabetes tends to occur in young,
lean individuals, usually before 30 years of age, however, older patients do
present with this form of diabetes on occasion. This subgroup is referred to as
latent autoimmune diabetes in adults (LADA). LADA is a slow, progressive form of
type 1 diabetes. Of all the patients with diabetes, only approximately 10% of
the patients have type 1 diabetes and the remaining 90% have type 2 diabetes.
Type 2 diabetes was also referred to as non-insulin
dependent diabetes mellitus (NIDDM), or adult onset diabetes mellitus (AODM). In
type 2 diabetes, patients can still produce insulin, but do so relatively
inadequately for their body's needs, particularly in the face of insulin
resistance as discussed above. In many cases this actually means the pancreas
produces larger than normal quantities of insulin. A major feature of type 2
diabetes is a lack of sensitivity to insulin by the cells of the body (particularly fat and muscle
cells).
In addition to the problems with an increase in insulin resistance, the
release of insulin by the pancreas may also be defective and suboptimal. In
fact, there is a known steady decline in beta cell production
of insulin in type 2 diabetes that contributes to worsening glucose control.
(This is a major factor for many patients with type 2 diabetes who ultimately
require insulin therapy.) Finally, the liver in these patients continues to produce glucose
through a process called gluconeogenesis despite elevated glucose levels. The
control of gluconeogenesis becomes compromised.
While it is said that type 2 diabetes occurs mostly in
individuals over 30 years old and the incidence increases with age, we are
seeing an alarming number patients with type 2 diabetes who are barely in their
teen years. In fact, for the first time in the history of humans, type 2
diabetes is now more common than type 1 diabetes in childhood. Most of these cases are a direct result of poor
eating habits, higher body weight, and lack of exercise.
While there is a strong genetic component to developing
this form of diabetes, there are other risk factors - the most significant of
which is obesity. There is a direct relationship between the degree of obesity and the
risk of developing type 2 diabetes, and this holds true in children as well as
adults. It is estimated that the chance to develop diabetes doubles for every
20% increase over desirable body weight.
Regarding age, data shows that for each decade after 40 years of age
regardless of weight there is an increase in incidence of diabetes. The
prevalence of diabetes
in persons 65 to 74 years of age is nearly 20%. Type 2 diabetes is also more
common in certain ethnic groups. Compared with a 6% prevalence in Caucasians,
the prevalence in African Americans and Asian Americans is estimated to be 10%,
in Hispanics 15%, and in certain Native American communities 20% to 50%.
Finally, diabetes occurs much more frequently in women with a prior history of
diabetes that develops during pregnancy (gestational diabetes - see below).
Diabetes can occur temporarily during pregnancy. Significant hormonal changes
during pregnancy can lead to blood sugar elevation in genetically predisposed
individuals. Blood sugar elevation during pregnancy is called
gestational
diabetes. Gestational diabetes usually resolves once the baby is born. However,
25%-50% of women with gestational diabetes will eventually develop type 2
diabetes later in life, especially in those who require insulin during pregnancy
and those who remain overweight after their
delivery. Patients with gestational diabetes are usually asked to undergo an
oral glucose tolerance test about
six weeks after giving birth to determine if
their diabetes has persisted beyond the pregnancy, or if any evidence (such as
impaired glucose tolerance) is present that may be a clue to the patient's
future risk for developing diabetes.
"Secondary" diabetes refers to elevated blood sugar
levels from another medical condition. Secondary diabetes may develop when the
pancreatic tissue
responsible for the production of insulin is destroyed by disease, such as
chronic pancreatitis
(inflammation of the pancreas by toxins like excessive alcohol), trauma, or surgical removal of the pancreas.
Diabetes can also result
from other hormonal disturbances, such as excessive growth hormone production
(acromegaly) and
Cushing's syndrome. In acromegaly, a pituitary gland tumor at the base of the
brain causes excessive production of growth hormone, leading to hyperglycemia.
In Cushing's syndrome, the adrenal glands produce an excess of cortisol, which promotes blood sugar elevation.
In addition, certain medications may worsen diabetes
control, or "unmask" latent diabetes. This is seen most commonly when steroid
medications (such as prednisone) are taken and also with medications used in the
treatment of HIV infection (AIDS).
Next: What are diabetes symptoms? »
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