|
|
|
National Statistics and Opportunities for Improved Surveillance,
Prevention, and Control
APPENDIX B
GENERAL INFORMATION DIABETES MELLITUS
This section summarizes current clinical information on diabetes mellitus
for the general reader, as well as relevant epidemiologic information
not available at the national level in Canada. Unless otherwise noted,
the information source for this section is Diabetes in America,
2nd Ed., National Institutes of Health, 1995. Additional information sources
include journal articles, and publications of the Canadian Diabetes Association
(CDA) and the Centers for Disease Control and Prevention (CDC) in the
United States.
DIABETES MELLITUS
Description
Diabetes mellitus is a condition resulting from an inability of the
body to sufficiently produce and/or properly use insulin. Insulin, a hormone
secreted from beta cells in the pancreas, assists with the conversion
of glucose into energy. Without insulin, glucose cannot be sufficiently
absorbed from the bloodstream into the cells of the body (primarily in
muscle, fat and liver tissue). Chronic high levels of blood glucose due
to diabetes are associated with long-term damage, dysfunction and failure
of various organs, especially the kidneys, eyes, nerves, heart, and blood
vessels.
There are three main types of diabetes: Type 1 diabetes, Type 2 diabetes,
and gestational diabetes. Impaired fasting glucose and impaired glucose
tolerance are conditions that can lead to diabetes. Most of our information
on diabetes in terms of life expectancy, complication rates, and risk
factors comes from US data sources.
- Type 1 Diabetes
Type 1 diabetes, previously known as insulin-dependent diabetes,
typically occurs in childhood or adolescence and requires multiple
daily injections of insulin for survival. The most common form of
Type 1 diabetes is caused by auto-immune destruction of beta-cells,
resulting in an inability of the pancreas to produce insulin. Type
1 diabetes may account for 5% to 10% of all diagnosed cases of diabetes(51).
According to US data, the reduction in life expectancy seen in people
with Type 1 diabetes is dependent on the age at diagnosis. At a minimum,
life expectancy is shortened by 15 years. One study using life insurance
records showed a reduction in life expectancy of 27 years in those
diagnosed before age 15. A study of patients at the Joslin Clinic,
a US clinic specializing in diabetes, found only a 16 to 17 year reduction
in life expectancy for those diagnosed at ages 10 or 15. However,
people who are treated at the Joslin Clinic would tend to be from
wealthier families and would likely receive better medical care.
- Type 2 Diabetes
Type 2 diabetes, previously known as non-insulin dependent diabetes,
typically begins after age 40. Type 2 diabetes may account for 90%
to 95% of all diagnosed cases of diabetes(51). The onset
of Type 2 diabetes is a two-stage process: (1) resistance to insulin's
action, often exacerbated by obesity, followed by (2) the pancreas
failing to increase insulin enough to compensate adequately. This
form of diabetes has recently been detected in Aboriginal youth and
is known as Paediatric Type 2 diabetes or Type 2Y diabetes ("Y" referring
to youth).
Life expectancy is reduced by 5 to 10 years in middle-aged people
with Type 2 diabetes. Life expectancy varies with age of onset, the
reduction being greater the younger the age at diagnosis.
- Gestational Diabetes Mellitus
Gestational diabetes mellitus (GDM) is defined as glucose intolerance
first recognized during pregnancy. Usually this form of diabetes is
a transient condition that disappears by six weeks postpartum. Gestational
diabetes is associated with an excess incidence of fetal macrosomia
("big babies"), pre-eclampsia, and Cesarean section. Women who have
had gestational diabetes are at increased risk for later development
of Type 2 diabetes. There is some evidence that Type 2 diabetes develops
in approximately one third of women who have ever had gestational
diabetes(52).
- Associated Conditions
People with blood glucose levels greater than those considered normal
but less than the level that is diagnostic of diabetes on standard
tests are classified as having impaired fasting glucose (IFG) (if
given a fasting glucose test), or impaired glucose tolerance (IGT)
(if given an oral glucose tolerance test). People in these groups
are considered to be at high risk for diabetes and/or its complications.
IFG or IGT prevalence rates are not available at the national level
in Canada. In the United States, an estimated 7% of the population
have IFG(51). A study conducted in the UK from 1990-1992
found the prevalence of IGT, based on World Health Organization criteria,
to be 16.8% among those 40 to 65 years of age(3) Researchers
are investigating how to predict which of those people with IFG or
IGT will go on to have diabetes and how to prevent such progression.
Symptoms and Diagnostic Testing
- Symptoms
The classic symptoms of diabetes mellitus are fatigue, polyuria
(frequent urination), polydipsia (unusual thirst), and unexplained
weight loss. In Type 1 diabetes, the symptoms usually progress quickly
and are often dramatic. In Type 2 diabetes, since symptoms are slower
to progress, it is possible to have no apparent symptoms and be diagnosed
on a non-related medical examination.
These symptoms are also compatible with diabetic ketoacidosis (DKA),
a condition resulting from absolute insulin deficiency and excess
contra-insulin hormones, which can lead to coma and death. DKA is
much more common among those with Type 1 diabetes. Before the discovery
of insulin, people with Type 1 diabetes usually died of DKA(34).
- Diagnostic Testing
The Canadian Diabetes Association (CDA) released new criteria for
the diagnosis of diabetes in 1998 in its revision of the Clinical
Practice Guidelines for the Management of Diabetes in Canada(14).
The new diagnostic criteria are based upon a number of recent studies
demonstrating that the previous diagnostic criteria using the fasting
plasma glucose test (FPG) lacked sensitivity (proportion of diabetes
cases accurately detected) compared with the sensitivity of the oral
glucose tolerance test (OGTT). However, the OGTT has problems of less
specificity (proportion of non-diabetes cases accurately identified)
compared with the FPG, as well as a lack of test-retest reliability.
Also, because the OGTT is a more difficult and expensive test to perform,
it has not received wide clinical acceptance.
The new FPG diagnostic criteria increase the sensitivity of that
test by lowering the cutpoint for a diagnosis of diabetes, from 7.8
to 7.0 mmol/L. The use of the new FPG criteria for a diagnosis of
diabetes should increase the number of people with diagnosed diabetes
as well as decrease the proportion of undiagnosed cases.
Treatment/Management of Diabetes
The primary goal of therapy for diabetes is the maintenance of the
patient's health in terms of his or her quality of life and overall
sense of well-being, as well as the avoidance of acute and chronic
complications. Since virtually every aspect of daily life may be affected
by treatment, the person with diabetes is the key member of the diabetes
health care team. For most people with diabetes, improving metabolic
control (such that blood glucose is near normal levels at all times)
will achieve the primary goal of preventing long-term complications.
Depending upon the type of diabetes and the therapy required to achieve
near normal levels of blood glucose, this objective may be more or
less difficult to achieve without causing acute side effects. The
metabolic goals of treatment/management must therefore be individualized.
Education of health care providers and of the people affected with
diabetes and their families is a cornerstone of effective treatment
and self-management of this condition.
- Type 1 Diabetes
Lack of insulin production by the pancreas makes Type 1 diabetes
particularly difficult to control. Treatment requires a strict regimen
that typically includes a carefully calculated diet, planned physical
activity, home blood glucose testing up to several times a day, and
multiple daily insulin injections(51).
- Type 2 Diabetes
Treatment typically includes diet control, exercise, home blood
glucose testing, and in most cases, oral medication and/or insulin.
Approximately 40% of people with Type 2 diabetes require insulin injections(51).
- Gestational Diabetes Mellitus
Treatment for women with gestational diabetes includes dietary counseling,
regular and moderate exercise, glucose monitoring, and insulin therapy
if diet alone does not achieve target blood glucose. The value of
treatment for gestational diabetes remains controversial.
Risk Factors for Diabetes
- Type 1 Diabetes - Risk Factors
Race and Ethnic Background. Race and ethnic background are
accepted risk factors for Type 1 diabetes. Rates are higher among
non-Hispanic whites than blacks or Hispanics in the United States.
Age. Incidence increases with age through childhood and adolescence
but decreases during adulthood.
Geographic Variability. Comparisons among countries facilitated
by the World Health Organization (WHO) have found the highest rates
of Type 1 diabetes in Scandinavia, intermediate rates in Canada and
the United States, and low rates in Japan and Tanzania.
Seasonal Variability. Most studies show some seasonal variation,
with incidence rates lowest in the warm summer months.
Genetic Susceptibility/Family History. Genetic susceptibility
is a factor in Type 1 diabetes but is not as strong a factor as in
Type 2 diabetes.
Possible Links to Diet and Exposure to Viruses. There is
some evidence of a protective effect of breast-feeding against Type
1 diabetes.
Note. Type 1 diabetes affects males and females equally.
- Type 2 Diabetes - Risk Factors Age. The prevalence
of Type 2 diabetes increases rapidly with age. The usual onset of diabetes
is after age 40.
Genetic Susceptibility/Family History. Increased risk of
diabetes with a positive family history of diabetes is probably due
to genetic and environmental factors. Evidence for genetic factors
comes from twin studies where the probability of finding diabetes
in both twins is twice as high among identical twins as fraternal
twins.
Obesity. Obesity is a well-recognized risk factor for diabetes.
Diabetes has been positively associated with each of the following:
(a) the level of obesity, (b) the duration of obesity, and (c) body
fat distribution (i.e., central deposition of fat).
Physical Inactivity. Physical inactivity is considered a
risk factor on the basis of observational and ecologic studies.
Ethnic Background. Ethnic background has been accepted as
an independent risk factor based on studies of high prevalence populations
(Aboriginal, Black, Hispanic), which have found increased risk for
diabetes among these populations compared with the white population
after controlling for all other known risk factors.
Note. High blood pressure and dyslipidemia (disturbances in lipoprotein
patterns, linked to coronary heart disease) are associated with diabetes,
although it is not clear at this time whether these factors contribute
to a person's risk of getting diabetes, or are caused by diabetes
itself. Gender is not an independent risk factor for Type 2 diabetes
in the general population. Smoking has been associated with diabetes
in a few studies but it is unclear if smoking is a causal factor in
the onset of diabetes. It is clear that smoking is a causal factor
for cardiovascular disease, one of the major complications of diabetes.
- Gestational Diabetes - Risk Factors
US studies have reported an increased risk of gestational diabetes
among African Americans, Hispanic/Latino Americans, American Indians,
and people with a family history of diabetes. Obesity is also associated
with higher risk.
Long-Term Complications of Diabetes
The main long-term complications of diabetes are as follows: (i)
microvascular disease, or small blood vessel damage, including retinopathy
(eye disease) and nephropathy (kidney disease); (ii) macrovascular
disease, or large blood vessel damage, including ischemic heart disease,
stroke, and peripheral vascular disease; (iii) neuropathy (nervous
system disease); and (iv) foot problems. Hypertension (high blood
pressure) is a risk factor for most complications of diabetes. There
is strong evidence that early diagnosis and tight control of blood
sugar levels and blood pressure can prevent or delay these complications.
- Cardiovascular Disease
The risk of heart disease is substantially increased for people
with diabetes. According to 1996 national survey data (NPHS 1996),
Canadians have 2 to 6 times (depending on age) the likelihood of having
heart diseases or stroke if they have diabetes as those without diabetes.
Heart disease is uncommon in those under 30 with Type 1 diabetes.
Adults with diabetes are more likely than those without to have risk
factors for heart disease, especially high blood pressure, low levels
of HDL cholesterol, and high levels of triglycerides. However, some
of the increased risk of heart disease associated with diabetes appears
to be independent of these factors.
- Kidney Disease (Nephropathy)
After 7 to 15 years, 25 to 40% of all patients with Type 1 diabetes
develop microalbuminuria. Of these, over 90% progress to proteinuria
over time. Kidney function declines at variable rates; it appears
to be a slower decline in Type 2 diabetes. After 10 years of persistent
proteinuria, the incidence of chronic kidney failure is 11% in those
with Type 2 diabetes and 50% in those with Type 1 diabetes.
- Blindness
Three complications of diabetes can lead to blindness: retinopathy,
cataracts, and glaucoma. Of people who have had diabetes for at least
15 years, 97% of insulin-taking patients and 80% of those not taking
insulin have retinopathy; the most severe manifestation, proliferative
diabetic retinopathy, occurs in 40% of those taking insulin and 5%
of those not taking insulin. Of people who have had insulin-dependent
diabetes for 30 or more years, 12% are blind. Diabetic retinopathy
is the leading cause of new cases of legal blindness among the working
age population.
- Nervous System Disease (Neuropathy)
Roughly 60% of people with diabetes have some degree of diabetic
neuropathy, and in half of these it develops within nine years of
diagnosis. Most have a mixed motor/sensory deficit resulting in decreased
sensation, increased sensitivity, pain, weakness, and muscle wasting.
Frequently, abnormal functioning of the autonomic (self-functioning)
nervous system leads to disorders of the heart and circulation, and
gastrointestinal and genitourinary tracts.
- Lower Extremity Amputations (LEA)
The risk of lower extremity (limb) amputations following diabetes
diagnosis is 6% at 20 years and 11% at 30 years. Lower limb amputations
are typically the result of a foot infection that does not heal and
eventually becomes gangrenous. The initial wound is often the result
of a lack of protective sensory function in the foot due to neuropathy.
The inability of the wound to heal properly is due to decreased blood
and nutrient flow to the lower limbs, the result of peripheral vascular
disease in most cases.
- High Blood Pressure (Hypertension)
An estimated 40% of people with diabetes in Canada have high blood
pressure. High blood pressure is one of the main risk factors for
cardiovascular disease.
- Dental Disease
Periodontal disease (a type of disease that can lead to tooth loss)
occurs with greater frequency and severity among people with diabetes.
Periodontal disease has been reported to occur among 30% of people
aged 19 years or older with Type 1 diabetes(51).
- Complications of Pregnancy (for women with pre-existing diabetes)
The rate of major congenital malformations in babies born to women
with pre-existing diabetes varies from 0% to 5% among women who receive
preconception care to 10% among women who do not. Between 3% and 5%
of pregnancies among women with diabetes result in the death of the
newborn; the rate among women who do not have diabetes is 1.5%(51).
- Other Complications
Diabetes can directly cause acute life-threatening events, such
as diabetic ketoacidosis and hyperosmolar nonketotic coma, as a result
of biochemical imbalance in uncontrolled diabetes. People with diabetes
are more susceptible to many other illnesses. For example, they are
more likely to die of pneumonia or influenza than people who do not
have diabetes(51).
[Previous] [Table
of Contents]
|
