Updated 11 April 2014

90% of cancers caused by us and our world

We can beat it if we clean up our act: over 90% of cancers are caused by our toxic environment and habits. Cancer is mostly made, not born.


Over 90% of cancers are caused by our toxic environment and lifestyle. Genes also matter, but to a far lesser degree.  

“Genes give us the gun, but environment pulls the trigger,” says internationally acclaimed scientist and writer Dr Devra Davis, speaking at the opening of the Cancer Association of South Africa (CANSA) Science and Resource Centre in Cape Town.

Davis, who is Professor of Preventive Medicine at Mt Sinai Medical Center in New York and author of The Secret History of the War on Cancer, points out that, although this is an indictment of the state the planet's in, it also means cancer can be effectively fought by making our homes and workplaces less toxic, healthier places.


What are ‘environmental’ factors?

In the context of cancer, “environmental” refers to all carcinogenic exposures from air, food, water and radiation, including tobacco smoke, a diet high in animal fats, X-rays and ultraviolet light – to name just some of the better known culprits on this growing list.


Others – specifically, certain man-made compounds like BPA and aspartame (more about these under "Clean up you act" below) – are less familar, but they’re well on their way to becoming household names – precisely because you wouldn’t want them in your household.

Cancer is mostly made, not born

Most babies are born with healthy genes, says Davis, which get progressively exposed to carcinogens as an individual goes through life. Exposed often and long enough, genetic material may mutate to produce cancerous cells. 


Identical twins are born with the same genetic makeup, but, as they age, their chromosomes appear increasingly different, displaying changes typical of chromosomal response to damage. If cancer were largely hereditary, then identical twins would have very similar risks for the disease. But in fact fewer than 50% of identical twins end up getting the same cancers. The cancer risk profile for adopted children, however, mirrors that of their adoptive, not their genetic, parents.


Further evidence for the overwhelming importance of environmental exposures comes from studies that show how workers exposed to much higher levels of known carcinogens (asbestos miners for example), have much higher corresponding rates of related cancers than the general public.


Rather safe than sorry

There may not be definitive proof from human studies yet for several suspected carcinogens, but, says Davis, “An absence of data isn’t proof of safety, and shouldn't be used as an excuse for inaction. Most cancers take decades to develop, and we can't afford to wait until research provides definitive answers before we take precautions. Safe is better than sorry.”


In the absence of human studies, growing evidence from animal studies must be taken much more seriously: “Every compound that causes cancer in humans has been shown, when thorough studies are conducted, to also cause cancer in animals. Thus if a compound is shown to cause cancer in animal studies we should view it as being very likely to be dangerous for people too.”


Prevention is key

Davis also stresses that we can't complacently put all our hopes into science finding a cure. There have been great clinical strides made - for example in treating leukemia and preventing cervical cancer (through use of the HPV vaccine), but for some cancers, such as lung and liver cancer, there has been no fundamental progress and the incidence of these illnesses is rising.


Greater prevention efforts are crucial, not least because, with ever-growing numbers of people being diagnosed, already over-burdened medical systems cannot cope, says Davis. 


“The US and South Africa have this in common, although it's worse for SA: we simply aren't going to have enough oncologists, oncology nurses, drugs and money to treat all the new cancer cases. We must reduce the demand for cancer treatment by doing all we can through prevention.”

Clean up your act

Here's a roundup of the latest information on some of the less well known, but likely or suspected environmental carcinogens, and what you can do to lower your exposure:


Bisphenol A and plastic bottles

Bisphenol A (BPA) is a man-made chemical used in the manufacture of certain plastic products. It’s ubiquitous in the modern world, cropping up in everything from credit cards to car interiors to… baby bottles.


But if BPA enters the human body this otherwise useful chemical has hormonal activity similar to the female hormone oestrogen, and can disturb biological processes at very low concentrations. Exposure to BPA is thought to increase the risk for breast cancer.


How are you exposed to it?

If BPA-containing plastics are heated, the BPA can be released. For example, if you pour hot milk into a BPA-containing baby bottle, the BPA can enter the hot milk – and the baby who drinks it.


It’s been found that 55 times more BPA is released from bottles filled with hot water compared to those with cold water.


How to avoid it

Dr Davis recommends avoiding plastics stamped with the number 7 (contains BPA), as well as 3 and 6 (contains similar chemicals that may be cause for concern).


“It’s the very hard plastic ones you need to beware of – they will say ‘PC’ for ‘polycarbonate’,"says Dr Carl Albrecht, Head of Research at CANSA. "The softer plastic ones, like those for bottled water, have not been shown to be harmful. But don't reuse them a lot – taking them repeatedly in and out of the fridge. Still, the main potential danger with that is bacterial contamination.”


As a general rule, rather than getting too worried about whether a bottle contains BPA or not, Albrecht agrees that it’s best to simply avoid heating any plastic bottle. Use glass instead. You can also boil water or milk in another container and then allow it to cool before pouring it into a plastic bottle.


Plasticisers and clingwrap

Plasticisers are chemicals – known as DEHP and DEHA – used to make plastic softer and more ‘sticky’. They’re the reason why plastic wrap clings – and why it’s so hard to smooth it out again once you’ve scrunched it up. They’ve been found to cause cancer in animal studies.


How are you exposed to them?

Plasticisers can migrate into the food they’re wrapped around – especially fatty foods like cheese and meat. This process is accelerated at high temperatures such as when cling-wrapped food is microwaved.


How to avoid it

After laboratory tests on various clingwrap brands, CANSA has given the nod of approval to Gladwrap, and in-house brands from Checkers, Pick ‘n Pay, Shoprite, SPAR and Woolworths – which are free of the offending chemicals.


You can also avoid using clingwrap by storing food in glass and plastic containers, or wrapping it in foil.


Trans fats

Trans fats, or trans fatty acids, are made (inadvertently) when plant oils are converted to margarine. In the 1990s, scientists realized that trans fats increased the risk of coronary artery disease. And now trans fats have been associated with breast cancer and prostate cancer.


How are you exposed to them?

You can ingest trans fats in many margarines and a lot of baked and fried goods.


How to avoid them

Margarines made by Unilever are free from trans fats. Examples include Flora, Rama, Stork and the SPAR house brand. Woolworths foods also do not contain transfats.



Acrylamide is a chemical that forms spontaneously in carbohydrate food at high temperature, especially in potato crisps - and coffee.

At this stage acrylamide is considered to be a probable human carcinogen, associated with kidney cancer, and post-menopausal and endometrial cancer. It is also neurotoxic.


How to avoid it

It may be premature to deny yourself the morning cuppa at this stage, but it’s never a bad idea to cut down. And we should all learn to live without the chips.



Dioxin refers to a group of toxic chlorinated organic compounds, produced as a by-product of many industrial processes, such as waste incineration and bleaching fibres.


Among the most toxic chemicals known, dioxins are long-lived in the environment and make their way into foods. They are soluble in fat, so they accumulate in the bodies of animals and humans over time. This means that small amounts are present in animal food products (meat and dairy). Thus, you can get dioxin in your body both by eating these foods and by inhaling emissions from pollutant sources.


Exposure has been linked to an array of negative health effects, including cancer, and reproductive and developmental problems.

How to avoid it

  • Reduce intake of animal fat, and choose low fat dairy.
  • Don't burn waste, and avoid environments where incineration is being carried out.


There is an ongoing debate among experts about the health risks associated with the artificial sweetener aspartame. Davis says she is very concerned about the long-term effects of this compound. "We don't know for sure if it's a human carcinogen, but the evidence from animal studies is pretty strong: prenatal aspartame exposure nearly doubles cancer rates in adult rodents, and tumours show up more as they age. It may be that we'll start seeing effects in humans with time."


How to avoid it

Sweeten your food with sugar or honey, or, if you need to reduce your sugar intake Davis recommends the sweetener stevia instead.


Cell phone radiation

Davis feels strongly that the "safe rather than sorry" principle should also apply to cell phone use. Cell phones emit low doses of microwave radiation, which can penetrate the brain. Children's heads absorb cell phone signals more readily because they are smaller, have thinner skulls and contain more fluid. Several countries (France, Britain, Germany, Finland, Israel and Bangalore India) are getting much stricter on cell phone use for kids, but in others - the US for one, cell phone companies are targetting children as young as five.

"We haven't been using cell phones very long," points out Davis. "Brain cancer can take 40 years to develop." Studies on cell phones have produced conflicting results, but, says Davis, many of those that found no significant risk for cancer did not follow research subjects for very long. Some studies suggest that the risk of developing brain tumours is doubled for people who've been using cell phones for 10 years or more. 

How to avoid it

Use cell phones with an earpiece and speakerphone so the phone is not held up against your head, and, says Davis, get into the habit of simply turning them off more often. She recommends that children under 12 should not use cell phones unless in emergencies.  Don't use your cell when only a few bars show - this means the radiation will be greater in order to get the signal through.

 (Olivia Rose-Innes, EnviroHealth Editor, Health24, January 2010)

 Read more:

Most cancers can be prevented
Lifestyle and diet as causal factors of cancer
16 ways to avoid cancer


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