Type 2 Diabetes and Obesity: What's the Connection?
By Irene S. Levine, Ph.D.
wo
recent studies on type 2 diabetes provide such striking evidence
about the link between this type of diabetes and obesity that
the findings may motivate even the most committed couch potatoes
to get up and exercise.
In a study involving data from the years 1990 to 1998, officials
at the Centers for Disease Control and Prevention (CDC) found
a staggering 70 percent increase in type 2 diabetes among Americans
between the ages of 30 and 39. Researchers attributed the whopping
increase to sedentary lifestyle and poor nutrition, which together
have caused obesity rates to rise in the United States.
The question of why obesity leads to type 2 diabetes has long
been a mystery, but now, scientists may finally have an answer.
Researchers at the University of Pennsylvania School of Medicine
recently reported the discovery of a hormone that may, for the
first time, explain the molecular basis for the connection between
diabetes and obesity.
Study one: alarming trends of obesity in the United States
Diabetes results in the failure of the body to either produce
or properly use insulin, the hormone necessary to convert sugars,
starches, and other foodstuffs into essential energy. This condition
is commonly referred to as insulin resistance. When this malfunction
occurs, the result is a buildup of glucose in the blood that can
pose serious health problems.
The disease has three variations: gestational diabetes, occurring
during pregnancy and usually disappearing afterward; type 1 diabetes,
which occurs in young children and adolescents and is sometimes
referred to as juvenile-onset diabetes; and type 2 diabetes, or
adult-onset diabetes, whose risk factors include old age and obesity
(see sidebar below). Type 2 is the most widespread of the three;
gestational and type 1 diabetes account for only 7 to 15 percent
of all diabetes cases in the United States
Underscoring the severity of the prevalence of type 2 diabetes,
a CDC study last year revealed a startling 33 percent increase
in the overall incidence of type 2 diabetes from 1990 to 1998.
There was a 70 percent increase in those aged 30 to 39, a 40 percent
increase in those aged 40 to 49, and a 31 percent increase in
those aged 50 to 59.
Obesity as a Risk Factor for Diabetes
While the causes of diabetes are not precisely known,
both genetic susceptibility and environmental factors
are presumed to play a role. According to the National
Diabetes Education Program's 2001 figures, several
factors place individuals at risk for type 2 diabetes.
These include:
- Being
older than 45
- Being
overweight
- Having
a close family member with diabetes
- Having
had diabetes during pregnancy
- Being
African American, Hispanic/Latino, Asian American
or Pacific Islander, or Native American
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Officials at the CDC also reported a striking 6 percent increase
in 1999 in the prevalence of type 2 diabetes among American adults
of all ages. This increase was observed in women and men of all
ages, across all ethnic groups, at all educational levels, and
across most of the United States.
The CDC faults a higher rate of obesity, which is one of the
major risk factors for diabetes, as the main cause for the elevated
numbers. Along with the CDC's diabetes figures, the prevalence
of obesity in this country rose nearly 6 percent during the same
study period.
Since there is a delay between the onset of obesity and the subsequent
development of diabetes, the rising statistics indicate that more
and more sufferers of type 2 diabetes will emerge as time passes.
"This dramatic new evidence signals the unfolding of an epidemic
in the United States," says Jeffrey Koplan, M.D., director of
the CDC, in a press release. "With obesity on the rise, we can
expect diabetes rates to increase sharply as a result. If these
dangerous trends continue at the current rates, the impact on
our nation's health and medical care costs in future years will
be overwhelming."
Study two: new hormone found from animal models
Although more than 80 percent of diabetics are known to be obese,
until recently there was no scientific explanation for the relationship
between type 2 diabetes and obesity. The discovery of a new hormone,
however, may provide the missing link between the two conditions.
In a series of experiments with mice, Claire Steppan, M.D., faculty
member in the department of endocrinology at the University of
Pennsylvania School of Medicine, and her colleagues discovered
a hormone produced by fat cells; they dubbed the new hormone resistin,
for resistance to insulin. Dr. Steppan and the other
researchers showed that the amount of resistin in the bloodstream
rose markedly in mice with both diet-induced and genetic forms
of obesity. And resistin levels in the mice decreased with the
administration of rosiglitazone, an antidiabetic drug.
Type 2 Diabetes: The Toll It Takes
Type 2 diabetes is the most common form of diabetes,
affecting 90 to 95 percent of the 16 million Americans
afflicted with the disease. In the past, type 2 diabetes
was often called non-insulin-dependent diabetes or
adult-onset diabetes. According to the CDC, approximately
800,000 new cases of diabetes are diagnosed each year;
more than 720,000 of these are type 2.
As one of the leading causes of death and disability
in the United States, diabetes takes an enormous toll
on society, both socially and economically. Those
with diabetes are at increased risk for serious medical
complications -- including blindness, kidney failure,
lower extremity amputation, and cardiovascular disease.
These complications account for an estimated $98 billion
annually in associated health care costs.
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The scientists also administered an anti-resistin antibody to
obese mice and were able to improve blood sugar and insulin action
in these mice. In a related experiment with standard-weight mice,
treatment with resistin interfered with glucose tolerance and
insulin action.
If humans and mice are found to react similarly to levels of
resistin, these findings could someday provide the basis for new
medications for type 2 diabetes. But experts are cautious, pointing
out that the study is preliminary. Since the effects of resistin
on the body as a whole remain a mystery, more research is needed
to explain the function of resistin as the link between obesity
and type 2 diabetes.
The role of lifestyle
Based on the findings of the two studies, it is more important
than ever for Americans to examine the lifestyle factors that
can place them at risk for type 2 diabetes. Frank Vinicor, M.D.,
director of the CDC's diabetes program, explains that "maintaining
healthy behavior such as controlling weight through nutrition
and physical activity can help ease the burden of diabetes, and
may actually prevent its onset."
So ask yourself: Are you sedentary? Do you get regular exercise?
Are you overweight? Do you watch your diet? If you already have
diabetes, are you working to improve your diet and increase your
level of exercise to better manage the disease? Are you educated
about diabetes?
Improvements to your lifestyle and greater knowledge about diabetes
can help you to manage the condition, or even prevent it altogether.
Isn't it time to get off the couch?
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