Chemicals in the environment

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.
Compounds in the environment that studies in lab animals have found to have estrogenlike
properties are of special interest. These 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
For a long time, studies found no link between cigarette smoking and breast cancer. In
recent years though, some studies have found that smoking might increase the risk of
breast cancer. The increased risk seems to affect certain groups, such as women who
started smoking when they were young. In 2009, the International Agency for Research
on Cancer concluded that there is limited evidence that tobacco smoking causes breast
cancer.
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 the link between smoking and breast cancer is also
not clear. 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.

Night work
Several studies have suggested that women who work at night—for example, nurses on a
night shift—may have an increased risk of developing breast cancer. This is a fairly
recent finding, and more studies are looking at this issue. Some researchers think the
effect may be due to changes in levels of melatonin, a hormone whose production is
affected by the body's exposure to light, but other hormones are also being studied.