Women who have ever had breast cancer might want to walk
away from the brie, the butter and the black cherry (and every other flavor)
According to a study of 1 893 women, breast cancer survivors
who average as little as one serving per day of high-fat dairy foods have a 49%
higher risk of dying from breast cancer than those who eat little or no
Cancer survivors at
risk of dying
In absolute terms, breast cancer survivors who consumed the
most high-fat dairy had about a 12% risk of dying of the disease. The elevated
mortality risk is therefore "modest," said lead author Candyce
Kroenke, a staff scientist at Kaiser Permanente, the nonprofit healthcare
"But since it may not be so difficult to lower your
consumption of high-fat dairy, I think if you have breast cancer it's
worthwhile."The research, published in the Journal of the National Cancer Institute, is notable because more
than a dozen studies since the late 1980s have examined whether consuming milk,
cheese, ice cream and other dairy products is related to breast cancer.
The results have been a confusing muddle: Some studies found
that women who eat a lot of dairy have a higher risk of breast cancer, others
found they have a lower risk and still others found no effect either way.
How the study was
The Kaiser study is the first to separate out the effects of
high- and low-fat dairy on women diagnosed with breast cancer. The hormone
connection might apply beyond breast cancer. A 2012 study found that drinking
more whole milk was associated with worse survival among men with prostate
cancer, while skim milk was associated with higher survival.
"This is a very well-done study by highly regarded
researchers," said Dr Michelle Holmes, associate professor of medicine and
epidemiology at Harvard Medical School and Harvard School of Public Health, who
was not involved in the research.
It advances scientists' understanding of how diet affects
breast cancer, she said, and presents women with a simple dietary choice:
"It's for each woman to decide, but if you don't eat high-fat dairy you
can get the same nutrients from other sources," including low-fat
Total dairy intake had no effect on how the women - who had
been diagnosed with stage 1, 2 or 3A invasive breast cancer and most of whom
were post-menopausal - fared over the 11.8 years, on average, that the
researchers tracked them.
Higher rate of dairy
But high-fat dairy, which means whole milk or cream and
anything made with them such as cheese and ice cream, did make a difference. Breast
cancer survivors who ate one or more servings per day (according to a 120-item
questionnaire they answered) also had a 64% greater risk of dying from all
causes, but that was expected: A high-fat diet has long been associated with
cardiovascular disease, among other illnesses.
The cancer risk was more surprising, if only because
scientists have speculated that the vitamin D and calcium in milk might protect
against cancer. Instead, the estrogens in milk might be the problem,
researchers say. These hormones, which promote some breast cancers, reside in
milk fat. Less milk fat means less oestrogens, so the oestrogen content of skim,
1% and 2% milk and products made from them is relatively low.
Another reason to suspect oestrogens rather than fat itself
was that eating more saturated fat of all kinds did not raise the women's
chances of dying of breast cancer as strongly as high-fat dairy did. That
suggests that fat consumption per se is unrelated to breast-cancer mortality:
nuts, chocolate, coconut and vegetable fats such as those in avocados did not
increase the risk.