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THURSDAY, 14 March 2013 (HealthDay News) -- Eating high-fat
dairy products may raise the risk of death years later for breast cancer
survivors, according to a new study that followed almost 1,900 women for up to
nearly 15 years.
High-fat dairy includes
foods such as whole milk, cream for coffee and butter. Low-fat dairy includes
skim milk, nonfat milk, low-fat yogurt or nonfat yogurt.
Women "who ate one
or more servings of high-fat dairy a day had a 49 percent higher risk of breast
cancer death compared to those who ate up to half a serving a day," said
study author Candyce Kroenke, a staff scientist with the Kaiser Permanente
Division of Research in Oakland, Calif.
The women in the
higher-intake group -- eating one serving or more a of high-fat dairy per day
-- had a 64 percent higher risk of dying from any cause compared to those who
consumed little or none, she added.
The link was much weaker
for high-fat dairy and a recurrence of the breast cancer, she said, and was not
strong enough to be significant statistically.
The study, supported by
the U.S. National Cancer Institute, is published March 14 in the Journal of
the National Cancer Institute.
Previous research by
others, Kroenke said, has not found that a low-fat diet protects against dying
from breast cancer.
She decided to explore
high-fat dairy foods since they contain more estrogens -- which tend to reside
in fat -- than do low-fat dairy foods. Breast cancers known as estrogen
receptor-positive (ER-positive) are more common than ER-negative and require
estrogen to grow.
The women in the new
study were diagnosed with early breast cancer between 1997 and 2000. They were
patients at Kaiser Permanente in California or were registered with the Utah
Cancer Registry.
Women supplied
information about their diet at the study start. Most also gave information on
diet six years later.
In all, 349 women had a
cancer recurrence over the follow-up period. Of the 372 women who died during
that time, 189 deaths (about half) were due to breast cancer.
The researchers divided
the women into three groups, from low to high intake of high-fat dairy foods.
The lowest group ate
less than a daily half-serving (or none) of high-fat dairy. The highest group
had a serving a day or more.
One limitation, Kroenke
said, is the reliance on self-reported food records, subject to mistakes as no
one remembers perfectly. So the link between high-fat dairy and death risk may
be underestimated, she said.
Kroenke accounted for
other factors that might play a role in cancer recurrence and death risk, such
as stage of cancer at diagnosis, education level and other diet habits.
There were not enough
women in the study to evaluate if the links between high-fat dairy and risk of
death held for women with both ER-positive and ER-negative cancers, she said.
"I would expect to
find a stronger link for ER-positive," she said.
Another expert commented
on the new research.
"This is really one
of the early studies of this topic," said Leslie Bernstein, director of
the division of cancer etiology in the Beckman Research Institute at the City
of Hope Comprehensive Cancer Center, in Duarte, Calif. She was not involved
with the new study.
"It's an
interesting finding,'' she said. But the researchers found an association, she
said, not a cause-and-effect link. "The women were not [randomly assigned]
to getting different diets."
Other factors could have
played a part. For instance, eating patterns may be different right after
diagnosis or treatment compared to earlier or later, she said.
The strongest result is
for high-fat dairy and risk of death from other causes, she said.
High-fat diets can cause
weight gain, a risk factor for heart disease. The women in the study who ate
high-fat dairy may have died mostly from cardiovascular disease, Bernstein
suggested, if they didn't die of breast cancer.
Both Kroenke and
Berstein agreed more study is needed.
Meanwhile, it wouldn't
hurt to eat low-fat dairy, Bernstein said.
"If women have
breast cancer and are trying to reduce their estrogen exposure, shifting away
from high-fat dairy to lower-fat dairy would make sense," Kroenke said.
SOURCES: Candyce
Kroenke, Sc.D., M.P.H., staff scientist, Kaiser Permanente Division of
Research, Oakland, Calif.; Leslie Bernstein, Ph.D., professor, and director,
division of cancer etiology, Beckman Research Institute, City of Hope
Comprehensive Cancer Center, Duarte, Calif.; March 14, 2013, Journal of the
National Cancer Institute
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