'Pre-diabetes' Raises Risk of
Dying from Cancer
Having too much insulin in the blood may
promote cancer production.
Previous studies have shown that people who have
difficulty processing blood sugar are at risk
of diabetes and heart disease. Now new research
suggests they may also be at increased risk of
dying from cancer.
The blood-sugar condition, known as impaired glucose
tolerance, is closely tied to excess weight and
lack of exercise.
Lead author Dr. Sharon H. Saydah stated that,
for the estimated 15 percent of U.S. adults older
than 40 who have it, the new study provides yet
another reason to modify a sedentary lifestyle.
"The finding may also explain why overweight
people are more likely to develop cancer, especially
colon cancer," said Saydah.
In a study of more than 3,000 adults, she and
her colleagues found that people with impaired
glucose tolerance were nearly twice as likely
to die from any type of cancer than were those
with normal blood sugar levels. Their risk of
dying from colon cancer, specifically, was more
than quadruple that of those without impaired
glucose tolerance.
Impaired glucose tolerance is marked by elevated
blood sugar levels as a result of resistance to
insulin, a hormone that helps convert sugar from
food into energy for the body's cells. Because
it often precedes type 2 diabetes, it is also
called pre-diabetes.
Current recommendations suggest that everyone
older than 50 receive regular colon cancer screenings.
But this new study suggests that people with pre-diabetes
should undergo such screening routinely, regardless
of their age.
The findings are based on a nationwide sample
of 3,054 adults ages 30 to 74 who were followed
between 1976 and 1980.
After adjusting for age, sex and other factors
associated with cancer risk, "abnormal glucose
tolerance remained strongly associated with cancer
mortality," the researchers report in the
American Journal of Epidemiology.
The reason for the linkage is unclear. Previous
studies have suggested that having too much insulin
in the blood may promote cancer production, since
insulin has been shown to stimulate cell growth,
especially in cells that line the colon.
However, people with actual diabetes -- diagnosed
or not -- were no more likely to die of cancer
than were people with normal blood sugar levels.
Again, the reasons are uncertain, but Saydah offered
several possible explanations.
"As a person moves from normal glucose tolerance
to impaired glucose tolerance to diabetes, their
insulin levels increase rapidly and then gradually
decline," she said. This decline "may
slow the cancer growth since there is not as much
insulin or associated growth factors available
for the cells."
Another potential reason, Saydah pointed out,
is that given that cardiovascular disease is the
leading cause of death among people with diabetes,
it may be that people with diabetes have undiagnosed
cancer and are simply dying from cardiovascular
disease first.
Offering yet a third possibility, Saydah said
that diabetes might offer some type of protective
effect.
"The theory behind this is that the blood
vessels of individuals with diabetes are stiffer
... possibly making it more difficult for cancer
cells to spread throughout the body," she
explained. "If the cancer stays more localized
it may be easier to treat and less likely to cause
death." American Journal of Epidemiology
2003;157:1092-1100.
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