Diet
and vitamin intake
Many studies have looked for a link
between certain diet and breast cancer risk, but so far the results have been
conflicting. Some studies have indicated that diet may play a role, while
others found no evidence that diet influences breast cancer risk. Studies have
looked at the amount of fat in the diet, intake of fruits and vegetables, and
intake of meat. No clear link to breast cancer risk was found. Studies have
also looked at vitamin levels, again with inconsistent results. Some studies
actually found an increased risk of breast cancer in women with higher levels
of certain nutrients. Also, so far, no study has shown that taking vitamins
reduces breast cancer risk. This is not to say that there is no point in eating
a healthy diet. A diet low in fat, low in red meat and processed meat, and high
in fruits and vegetables may have other health benefits.
Most studies have found that breast
cancer is less common in countries where the typical diet is low in total fat,
low in polyunsaturated fat, and low in saturated fat. On the other hand, many
studies of women in the United States have not found breast cancer risk to be
related to dietary fat intake. Researchers are still not sure how to explain
this apparent disagreement. It may be at least partly due to the effect of diet
on body weight (see below). Also, studies comparing diet and breast cancer risk
in different countries are complicated by other differences (like activity
level, intake of other nutrients, and genetic factors) that might also change
breast cancer risk.
More research is needed to better
understand the effect of the types of fat eaten on breast cancer risk. But it
is clear that calories do count, and fat is a major source of these. High-fat
diets can lead to being overweight or obese, which is a breast cancer risk
factor. A diet high in fat has also been shown to influence the risk of
developing several other types of cancer, and intake of certain types of fat is
clearly related to heart disease risk.
The American Cancer Society
recommends eating a healthy diet with an emphasis on plant sources. This
includes eating 5 or more servings of vegetables and fruits each day, choosing
whole grains over those that are processed (refined), and limiting consumption
of processed and red meats.
Antiperspirants
Internet e-mail rumors have
suggested that chemicals in underarm antiperspirants are absorbed through the
skin, interfere with lymph circulation, cause toxins to build up in the breast,
and eventually lead to breast cancer. There is very little laboratory or
population-based evidence to support this rumor.
One small study has found trace
levels of parabens (used as preservatives in antiperspirants and other
products), which have weak estrogen-like properties, in a small sample of
breast cancer tumors. But this study did not look at whether parabens caused
the tumors. This was a preliminary finding, and more research is needed to
determine what effect, if any, parabens may have on breast cancer risk. On the other
hand, a large study of breast cancer causes found no increase in breast cancer
in women who used underarm antiperspirants and/or shaved their underarms.
Bras
Internet e-mail rumors and at least
one book have suggested that bras cause breast cancer by obstructing lymph
flow. There is no good scientific or clinical basis for this claim. Women who
do not wear bras regularly are more likely to be thinner or have less dense
breasts, which would probably contribute to any perceived difference in risk.
Induced
abortion
Several studies have provided very
strong data that neither induced abortions nor spontaneous abortions
(miscarriages) have an overall effect on the risk of breast cancer.
Breast
implants
Several studies have found that
breast implants do not increase breast cancer risk, although silicone breast
implants can cause scar tissue to form in the breast. Implants make it harder
to see breast tissue on standard mammograms, but additional x-ray pictures
called implant displacement views can be used to examine the breast tissue more
completely.
Chemicals
in the environment
A great deal of research has been
reported and more is being done to understand possible environmental influences
on breast cancer risk.
Of special interest are compounds in
the environment that have been found in lab studies to have estrogen-like
properties, which could in theory affect breast cancer risk. For example,
substances found in some plastics, certain cosmetics and personal care
products, pesticides (such as DDE), and PCBs (polychlorinated biphenyls) seem
to have such properties.
This issue understandably invokes a
great deal of public concern, but at this time research does not show a clear
link between breast cancer risk and exposure to these substances.
Unfortunately, studying such effects in humans is difficult. More research is
needed to better define the possible health effects of these and similar
substances.
Tobacco
smoke
Most studies have found no link
between cigarette smoking and breast cancer. Some studies have suggested
smoking increases the risk of breast cancer, but this remains controversial.
An active focus of research is
whether secondhand smoke increases the risk of breast cancer. Both mainstream
and secondhand smoke contain chemicals that, in high concentrations, cause
breast cancer in rodents. Chemicals in tobacco smoke reach breast tissue and
are found in breast milk.
The evidence on secondhand smoke and
breast cancer risk in human studies is controversial, at least in part because
smokers have not been shown to be at increased risk. One possible explanation
for this is that tobacco smoke may have different effects on breast cancer risk
in smokers and in those who are just exposed to smoke.
A report from the California
Environmental Protection Agency in 2005 concluded that the evidence about
secondhand smoke and breast cancer is "consistent with a causal
association" in younger, mainly premenopausal women. The 2006 US Surgeon
General's report, The Health Consequences of Involuntary Exposure to Tobacco
Smoke, concluded that there is "suggestive but not sufficient"
evidence of a link at this point. In any case, this possible link to breast
cancer is yet another reason to avoid secondhand smoke.
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