(Reuters Health) – People who are obese have a
greater risk of developing and dying from several types of cancer
including malignancies of the breast, ovary, kidney, pancreas,
colon, rectum and bone marrow, a research review confirms.
Cancer is a leading cause of death worldwide,
and the prevalence of obesity has more than doubled over the past
generation. Even though excess weight is thought to influence the
odds of developing and dying from a wide variety of tumors, the
study found “strong evidence” supporting this connection for just
11 cancers.
“Other associations could also be genuine, but
there is still substantial uncertainty about them,” lead study
author Dr. Maria Kyrgiou of Imperial College London said by
email.
Globally, 1.9 billion adults are overweight or
obese, according to the World Health Organization. Roughly four in
10 adults are overweight, and more than one in 10 are obese, a
condition that increases the risk of heart disease, diabetes,
kidney problems and joint disorders in addition to certain
cancers.
For the current study, researchers analyzed
results from 204 previously published studies exploring the
connection between obesity, weight gain, waist circumference and 36
different cancers.
Researchers looked in particular for evidence
that the previous results might have exaggerated the link between
obesity and cancer or found a connection that was too small to rule
out the possibility that it was due to chance.
They found the strongest links were between
obesity and malignancies of the digestive organs and for
hormone-related tumors in women, according to the report in The
BMJ.
When researchers looked at what’s known as
body mass index (BMI), a ratio of weight to height, they found
increases in BMI tied to a higher risk of developing cancers in the
esophagus, bone marrow, biliary tract system, pancreas and kidney.
Upticks in BMI were also linked to greater odds of colon and rectal
cancers in men as well as endometrial malignancies in younger
women.
A BMI between 18.5 and 24.9 is considered a
healthy weight, while 25 to 29.9 is overweight, 30 or above is
obese and 40 or higher is what’s known as morbidly obese. (The
National Heart, Lung and Blood Institute has an online BMI
calculator here: bit.ly/1D0ZqDv.)
The increased risk of cancer for every 5-unit
gain in BMI ranged from 9 percent for rectal cancer among men to 56
percent for tumors in the biliary tract system.
For women, weight gain and extra belly fat, a
measurement known as waist-to-hip circumference ratio, were also
associated with an increased risk of certain cancers.
After menopause, women’s risk of breast cancer
increased by 11 percent for every 5 kilograms (11 pounds) of weight
they gained during adulthood. This was in women who didn’t take
hormones to ease menopause symptoms, a treatment that is
independently linked to an increased risk of breast cancer.
As women added more fat around the midsection,
every 0.1 unit increase in waist-to-hip ratio was associated with a
21 percent jump in the odds of endometrial cancer.
Researchers found strong evidence linking
weight gain to colorectal cancer. They also found a strong
connection between BMI increases and getting cancers of the
gallbladder, stomach and ovaries, as well as dying from bone marrow
tumors.
One limitation of the study is that
researchers didn’t examine controlled experiments designed to prove
that obesity directly causes cancer, the authors note.
More research is needed that assesses changes
in body fat over time to better understand how obesity directly
influences the risk of getting cancer or dying from the disease,
the authors conclude.
The way obesity impacts the risk of cancer
also varies in different parts of the body, Dr. Graham Colditz, a
researcher at Washington University School of Medicine in St.
Louis, said by email.
But the take-home message is the same for
every patient, added Colditz, author of an editorial accompanying
the study.
“Avoiding weight gain through adult years is
important,” Colditz said. “Even if you are overweight focus first
on not gaining any more weight; for those who are overweight or
obese taking off some pounds can lower cancer risk.”
SOURCE: bit.ly/2ldy6nM and bit.ly/2lXEmgB The
BMJ, online February 28, 2017.
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