Thursday June 25 2015
Researchers looked at combinations of chemicals
“Fifty everyday chemicals…could be combining to increase our risk of cancer” the Daily Mail reports.
Researchers have identified 85 chemicals which have the potential to cause cells to switch into “cancer mode” – that is replicate at a dangerous rate inside the body. And fifty of them could have this effect at the low dose level that we are exposed to in the environment. However, the researchers also found that over half of them also had protective effects against the development of cancer.
Currently, the safety of a chemical is looked at on its own. The researchers are calling for chemicals such as those in this list to be looked at in combination when assessing their safety. This is because they think that exposure to a combination of chemicals acting on different characteristics could be important in the development of cancer.
It is important to put the risk associated with these “everyday chemicals” in context. There is little point in worrying about handcream if you are smoking 20 cigarettes a day or avoiding suncream so you get exposed to high levels of cancer-causing ultraviolet radiation.
Where did the story come from?
The study was carried out by an international panel of experts and was funded by a large number of foundations and government medical programs across the globe. It was called The Halifax Project and the initial kick-off meeting was held in Halifax, Nova Scotia.
The study was published in the peer-reviewed medical journal Carcinogenesis on an open access basis so it is free to read online or download as a PDF.
The Daily Mail confusingly tried to reassure the public by saying “the 50 chemicals were safe in low doses”, while having large headlines such as “From chips to perfume, the danger list”. They also did not make it clear that the researchers do not know what effect combinations of the chemicals would have. The media failed to point out that over half of the chemicals identified also had cancer prevention effects.
What kind of research was this?
This was a series of systematic reviews to collate evidence of chemicals in the environment that can affect different stages in the development of cancer.
The review reports that the World Health Organisation (WHO) and the International Agency for Research on Cancer (IARC) estimate that 7% to 19% of cancers are due to exposure to toxic substances in the environment. For example it is estimated that the naturally occurring radioactive gas radon is responsible for 3% of all lung cancer cases in England.
Here they wanted to explore their hypothesis that exposure to low doses of multiple chemicals may combine to cause cancer.
Chemicals are usually tested individually in animal studies to determine what dose is harmful. This is then used to estimate the level at which the chemical is likely to be harmful to humans. Safety margins for low dose exposure are then worked out. The researchers say that this approach could miss chemicals that do not individually cause cancer, but do when combined with others. They wanted to create a list of chemicals that affect each stage of cancer development so that future research could look at the effect of combining some of these chemicals at low doses.
What did the research involve?
An international collaboration was established including an initial 703 experts. They had different backgrounds including cancer biologists, environmental health experts, toxicologists (specialists who look at the effects of chemicals on living organisms) and endocrinologists (clinicians who look at hormonal disorders).
Eleven teams were created from this large international pool of researchers. One team looked at the development of cancer as a whole, while each of the other teams looked at one of the following ten characteristics (or hallmarks) of cancer:
- unlimited cell growth
- insensitivity to signals to stop growing
- resisting internal signals for cell death
- cell death no longer occurring after a certain number of cell divisions
- ability to make new blood vessels form to feed the tumour
- invasion of tissues and spread to other organs
- spread of the mutation in the DNA
- creation of inflammation which helps the tumour to grow
- resisting destruction by the immune system
- disturbance in metabolism which provides more energy for the cancer
The teams were asked to describe their allocated characteristic and up to 10 biological targets that could cause the characteristic. They then drew up a list of up to chemicals that are commonly found in the environment which have been shown to cause disruption to these 10 biological targets. They excluded any chemicals that are known to directly cause cancer. They also excluded any chemicals that are linked to cancer through “lifestyle” such as tobacco, red meat and lack of fruit and vegetables.
A separate team of researchers then looked at whether these chemicals had an effect on more than one characteristic.
What were the basic results?
In total, the researchers reviewed the evidence of 85 chemicals that have the potential to cause the characteristics of cancer without currently being known to cause cancer. Fifty of them were found to be able to cause these changes at the type of low doses that might be encountered in the environment. Information was not available on the level of dose required for 22 chemicals and 13 chemicals only caused the changes at a higher dose. Over half of the chemicals also had protective effects against the cancer characteristics.
The chemicals identified as potentially harmful in several areas included:
- sulphur dioxide
- paraquat (weedkiller)
- phthalates (substances that soften plastic and are in some cosmetics)
- titanium dioxide (used in sunscreen and as a whitener)
How did the researchers interpret the results?
The researchers concluded that further research is needed to investigate the effect of a combination of low doses of chemicals to see if their theory is correct. They say that this is a new way of looking at the causes of cancer and should be incorporated in the WHO International Programme on Chemical Safety, rather than looking at exposure to chemicals individually. The researchers say that there results have been compiled as a starting point for future research into mixtures of chemical exposure.
This systematic review has identified 85 chemicals that are found in the environment that have the potential to affect different stages in the development of cancer. The researchers say that this is intended to be a starting point so that future research can look at what effect these chemicals may have when there is exposure to more than one. This is a new approach to understanding the risk that various chemicals may have.
The study has not found that these chemicals cause cancer, but rather that they have the potential to make changes to cells which would then create particular characteristics of cancer such as increased uncontrolled cell growth.
The researchers acknowledge that the development of cancer is complex and that it is caused by a combination of genetic susceptibility, environmental factors and exposures to toxins such as through smoking. They hope that this research can pave the way for further understanding of how these factors combine.
A limitation of this study is that it was reliant on previous research and available literature. Many of the studies only provided short-term toxicity data and not long-term exposure to the chemicals. The study types were also of varying quality.
This study will be of importance to regulators when considering how to assess the toxicity of chemicals and whether this needs to be done in combination rather than just individually.
From what we know the most effective methods of reducing your risk of cancer are regular exercise, a healthy diet with no more than 70g of red meat a day, quit smoking if you smoke, protect your skin from the sun and don’t drink too much alcohol.
Read more about cancer prevention