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. But the evidence linking such chemicals to cancer has generally been poor or inconsistent.
Concerns have focused on a group of chemicals that could mimic or disrupt the effects of human hormones, like oestrogen. This group of chemicals has several names including 'hormone mimics' and 'endocrine-disrupting chemicals' (EDCs). You may also have seen stories in the media about specific chemicals, such as phthalates or triclosan - these are specific EDCs.
EDCs are a diverse group of chemicals and can be found all around us in thing like plastics, pesticides, fungicides, vehicle exhaust fumes and solvents. So we can be exposed to them by eating or drinking affected food or water, absorbing them through our skin, or indeed breathing in EDCs that are in the air. The worry is that EDCs could disrupt the action of hormones in our bodies, leading to health problems, including cancer.
Hormone mimics and cancer
Some people suggest that the increasingly common use of EDCs explains why breast cancer, prostate cancer and testicular cancer have become much more common in the last century. But there is no good direct evidence to support this.
A number of other things are likely to have contributed to the increase in rates of breast cancer over the last few decades. 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 alcohol. All of these are known risk factors for breast cancer.
There has also been a trend towards more prostate cancers being diagnosed in men. Much of this is linked to the introduction of PSA testing, which has led to some prostate cancers being diagnosed that would otherwise have gone unnoticed and not caused any harm. More early stage prostate cancers are also being diagnosed in men who have a transurethral resection of the prostate (TURP), an operation that is often used to treat men with a non-cancerous swelling of their prostate.
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.
We know that hormones are linked to the development of some cancers, including breast, prostate, testicular and womb cancers. But at the moment scientists don't fully understand what goes wrong in the body to allow our own hormones to cause cancer. Without understanding this, it's also hard to explain how EDCs could cause cancer. Studies with animals and cells have shown that EDCs can disrupt hormone interactions and cause cancer in the laboratory. So it is possible that EDCs could cause cancer in people, but we don't know for sure.
Some studies suggest that EDCs from pesticides may be linked to cancer in people who are exposed to high levels of pesticides as part of their job, such as farmers or people working in industry.
What needs to be done?
To get a clear answer, scientists will need to do large, carefully-designed studies looking at people and their exposure to environmental chemicals. So while there is no strong evidence at the moment that EDCs cause cancer in people, we cannot rule this out either.
There are a number of things that make it difficult to get reliable evidence from studies that have looked at environmental EDCs and cancer in people:
- Small numbers of people. Many studies have not included very many people, which makes it more likely that any findings are due to chance.
- The level of EDCs. Many studies are based on particular groups of people who are exposed to very high levels of EDCs, like farmers or industry workers. It is not clear if the much lower levels of EDCs that the general public is likely to be exposed to are linked to cancer.
- Measuring exposure. Some studies look at a person's job title to see if they might have been exposed to EDCs and for how long, which is not always reliable. Or people are asked to remember when they have been exposed in the past, which may be difficult. Their answers may also be influenced by whether they are worried about EDCs being responsible for their cancer.
- Correcting for other things. Many EDC studies have not taken other things into account that can affect a person's cancer risk. There are a number of things, including people's age, whether they smoke or not, how much alcohol they drink and whether they maintain a healthy weight and eat a healthy diet that can influence people's risk of developing cancer. It is important that researchers look at these when interpreting the findings from a study.
- The number of EDCs. There are many groups of products that contain EDCs, including pesticides, plastics or fuels, and it is not clear which, if any, affect the risk of cancer. It's also not clear whether certain combinations of EDCs could affect the risk of cancer, even though each one by itself may not have an effect.
- The length of the study. Cancer can take many years to develop and some studies happened too recently to know if the EDCs investigated could be linked to cancer.
Whether or not EDCs 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, either during pregnancy or before, could experience problems in later life. More research is therefore needed to get a clearer answer about EDCs and their possible effects on people, including the risk of cancer. NHS Choices published a blog post in response to a 2013 report on EDCs by the World Health Organisation. This report also highlights the need for more research.
Cancer Research UK is funding a number of projects looking at hormones and cancer to help us understand this better. We fund researchers like Professor Jack Cuzick and Professor Valerie Beral who are working to find ways to prevent hormone related cancers, like breast and prostate cancers. And we have already made good progress in improving treatment for breast and prostate cancers.
Until we know more about EDCs and cancer in people, it is important to bear in mind that there are a number of things that we know we can do to minimise our risk of cancer. A study published in 2011 calculated that more than 4 in 10 cancers could be prevented through healthier lifestyles. Smoking, body weight, diet, alcohol and physical activity are all things that we know affect our risk of developing cancer and they are all within our control to change.
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