Hormones in our environment - do they affect our risk of cancer?
There is a lot of public concern about the man-made chemicals in our food, environment and household goods. The evidence linking such chemicals to cancer has generally been poor or inconsistent.
Recently, concerns have focused on a group of chemicals that are similar to human hormones, such as oestrogen, and could mimic their effects. These chemicals have several names including ‘hormone mimics’ and ‘endocrine-disrupting chemicals’ (EDCs). The worry is that EDCs could disrupt the action of hormones in our bodies, leading to health problems, including cancer.
EDCs include a large number of pesticides, which are covered in more detail in our Cancer Controversies section. And our Harmful Substances section has more information about environmental chemicals and cancer.
Hormone mimics and cancer
Some people suggest that the increasingly common use of EDCs explains why breast cancer and testicular cancer have become much more common in the last century. But the evidence either fails to support this idea, or contradicts it.
For breast cancer, the main suspects are a group of EDCs called organochlorines, commonly used as pesticides. However, the vast majority of studies have found that organochlorines are not a cause of breast cancer.
The growing numbers of breast cancers in the last few decades can be explained by other changes. These include the trend towards having smaller families later on in life, and the increasing number of women who are overweight or obese, or drink heavily.
Some scientists have suggested that men may have higher risks of testicular cancer if their mothers were exposed to high levels of EDCs while pregnant. But this is still just a theory and there is very little direct evidence to support it. The trends also show that testicular cancer numbers started increasing in the 1920s. This was long before the large increases in EDC use in the mid-to-late twentieth century.
Our own hormones are much stronger
We do know that the effects of EDCs are very weak. While they can mimic the hormones in our bodies, they are several times less strong. This means that any effects they may have on cancer risk are likely to be overpowered by the effect of our own natural hormones.
For example, scientists have found that obese women can have up to twice as much oestrogen as women with a healthy weight. It is unlikely that EDCs could raise oestrogen levels to such a high extent.
However, some EDCs can also trigger our bodies to produce more of their own hormones. So far, there is no strong evidence that these indirect effects could affect our risk of cancer. But they still pose a potential danger which needs to be investigated further.
What needs to be done?
It is very hard to measure a person’s exposure to environmental chemicals. So while there is no strong evidence that EDCs can cause cancer in people, we cannot rule this out either. To get a clear answer, scientists will need to do large, carefully-designed studies.
Even if studies find that EDCs are linked to cancer, their effects are likely to be very small. Other lifestyle factors such as smoking, body weight, diet and alcohol are likely to have a much larger effect on cancer risk.
Whether or not they are linked to cancer, these chemicals have been tied to other health problems, including infertility and reproductive problems. These issues will also need to be studied carefully. In particular, researchers must work out if the children of mothers who are exposed to EDCs could experience problems in later life.
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