Type 1 diabetes may increase the
risk for some forms of cancer but lower the risk for others. This is according
to new research published in the journal Diabetologia.
Type 1 diabetes has been linked to increased risk of stomach, pancreatic, liver, kidney and endometrial cancers in the new study.
Type 1 diabetes accounts for around 5% of
all diabetes cases, occurring when the pancreas is
unable to produce the hormone insulin, resulting in high blood glucose
levels, or hyperglycemia.
Study coauthor Dr. Stephanie Read,
of the Usher Institute of Population Health Sciences & Informatics at the
University of Edinburgh in the UK, and colleagues note that previous studies
have suggested that people with diabetes have a 20-25% greater risk of cancer than those without diabetes.
However, they point out that the
populations of such studies have primarily consisted of people with type 2 diabetes, given that it is the most
common form of diabetes, accounting for 90-95% of all cases. This means the
association between type 1 diabetes and cancer is less clear.
"It is possible that the relationship
between type 1 diabetes and cancer is different from that observed between type
2 diabetes and cancer as a result of differences in the underlying disease
characteristics, drug therapies and patterns of risk factors, such as obesity," the authors note.
As such, Dr. Read and colleagues
compared cancer incidence among individuals with type 1 diabetes across five
countries, with the aim of gaining a better understanding of the link between
the two conditions.
Increased
risk of site-specific cancers
The researchers identified people
with type 1 diabetes - under the age of 40 - using nationwide diabetes
registers from five countries: Australia, Denmark, Finland, Scotland and
Sweden. They monitored these individuals for cancer incidence, identifying
9,149 cancers across 3.9 million person-years.
The team linked the data with
information from national cancer registries in each country, allowing them to
compare the cancer incidence of people with type 1 diabetes with that of the
general public.
Looking at overall cancer risk, the
researchers found that men with type 1 diabetes were at no higher risk than men
without the condition. Women with type 1 diabetes, however, were found to have
a 7% greater overall cancer risk than women without type 1 diabetes.
When it came to specific cancers,
the researchers found that men with type 1 diabetes were 23% more likely to
develop stomach cancer,
while women with type 1 diabetes were at 78% greater risk for the disease,
compared with the general public.
Both men and women with type 1
diabetes were also at greater risk for cancers of the liver (two-fold for men,
55% for women), pancreas (53% for men, 25% for women) and kidney (30% for men,
47% for women), while women also had a 42% increased risk for endometrial
cancer.
Lower
risk of prostate, breast cancers
However, the researchers also found
that women with type 1 diabetes had a 10% reduced risk of breast cancer, while men
with type 1 diabetes had a 44% reduced risk of prostate
cancer, which the team says may explain why no increased overall
cancer risk was identified among men with type 1 diabetes.
Fast facts about type 1 diabetes
- Around 1.25 million children and adults in the US have type 1 diabetes
- Type 1 diabetes is most commonly diagnosed in children and young adults
- The condition is primarily managed through multiple daily injections with insulin pens or syringes or an insulin pump.
While the authors cannot explain
exactly why type 1 diabetes was associated with a lower risk of breast and
prostate cancers, they have some theories.
Reduced risk of breast cancer among
women with type 1 diabetes in the study may be down to the younger cohort,
which consisted of fewer postmenopausal women among whom breast cancer is most
common.
The lower risk of prostate cancer
identified, the researchers speculate, could be down to lower testosterone
levels often found among men with type 1 diabetes.
"Higher testosterone levels
were previously shown to lead to an increased risk of prostate cancer, while
hyperglycemia has also been shown to inhibit testosterone production," the
authors explain.
The researchers also found that the
risk of cancer was highest in the first year after a diabetes diagnosis; cancer
incidence was 2.3 times higher for both men and women in the 12 months after
being diagnosed with type 1 diabetes.
The team suggests that this finding
is likely down to identification of pre-existing cancers soon after a diabetes
diagnosis rather than a result of diabetes itself, noting that cancers are more
likely to be detected when a patient is receiving more medical attention.
For most specific cancers, the risk
reduced with increasing duration of type 1 diabetes, though the researchers
note that the risk of endometrial cancer for women remained elevated for around
18 years after type 1 diabetes diagnosis.
For men, cancer incidence overall
fell to a level comparable to that of the general public after around 20 years
of having type 1 diabetes. For women, cancer incidence fell to the level of the
general population after 5 years of having type 1 diabetes.
Increased
cancer risk 'unlikely a result of insulin therapy'
Previous studies have suggested that
insulin therapy may be to blame for increased cancer risk for diabetes
patients, but Dr. Read and colleagues say their findings indicate this is not
the case.
They explain that if insulin
treatment was a key risk factor for cancer, their results would have shown a
higher cancer incidence for people with type 1 diabetes than those with type 2,
given that a significantly smaller number of people with type 2 diabetes are
treated with insulin.
"Furthermore, the absence of an
association between overall or site-specific cancer risk and increasing
duration of diabetes in our study does not support a dose-response relationship
between exogenous insulin use and cancer incidence," they add.
Instead, the researchers suggest the
observed increased risk of certain cancers among people with type 1 diabetes
may be down to shared metabolic deficiencies in people with type 1 and type 2
diabetes, such as high blood glucose levels.
"Hyperglycemia may be a
plausible explanation given the identification of a dose-response relationship
between glycated hemoglobin levels and the risk of certain cancers," they
explain.
While these findings shed light on
the association between type 1 diabetes and cancer risk, the authors say the
results "do not support changing the policy for screening in persons with
type 1 diabetes." They add:
"Similar recommendations for
lifestyle approaches to reduce cancer risk such as weight management,
increasing physical activity and avoiding smoking apply to persons with type 1
diabetes as for the general population.
Future work should be directed at
ascertaining whether the increased incidence of some cancers among persons with
type 1 diabetes leads to a raised risk of cancer mortality among persons with
type 1 diabetes."
Source: Medical News Today
