Note: in the original source, the titles for sections 4 and 5 were reversed. This appears to be an error, and is corrected below. - gotbeer

Truth about the cancer trap

What to believe after a spate of scare stories in the media? We separate the science from the hype

Felicity Lawrence, Ian Sample and Alok Jha

Thursday, January 15, 2004, The Guardian

http://www.guardian.co.uk/life/feat...1122913,00.html

No, you shouldn't. Yes, you should. If it weren't so serious, there might have been something funny about the row between scientists either side of the Atlantic about how much salmon we should all eat.

American scientists have told us that to eat Scottish salmon more than three times a year could increase our risk of cancer. British experts, having duly considered the science of risk assessment, said we could ignore them and eat fish, including salmon, twice a week. Then an English researcher said she had found cancer-causing chemicals from deodorant in women's breast tumours. She speculated that the British predilection for this form of toiletry might account for the dramatic rise in breast cancer in this country. Other experts pointed out that breast cancer has many causes.

If you like fish, and prefer not to sweat, you could have been forgiven for feeling confused. Heaven help you if you were reading the reports over a cup of coffee - did you know that caffeine increases the risk of cancer in humans but cures skin cancer in mice? Inevitably when these apparently new risks hit the news, it is hard for most of us to work out their significance. Risk factors do not work in isolation.

The US salmon researchers looked at the maximum amount of salmon that could be eaten before boosting cancer risk by at least 1 in 100,000, based on the US environmental protection agency guidelines that the dioxins found in salmon are toxic in laboratory animals and therefore any exposure carries some risk. But the UK food standards agency assessed the risks by looking at other guidelines which have established safety levels by taking into account the mechanism by which compounds cause cancer. The salmon in question was within WHO safety levels, and given all the other health benefits of eating salmon, the FSA calculated the benefits outweighed the risks.

These apparently conflicting messages underline the difficulties of assessing risk, particularly for diseases whose causes are complex. Although the headlines implied it, no one is saying that there is a straightforward cause and effect: eat salmon/use deodorant/drink caffeine and you'll get cancer.

The full research paper on salmon, which appeared in Science, is respectably cautious. "The risk/benefit computation is complicated," it says.

What experts can say is that more than one in three of us will develop cancer at some point, and that one third of all cancers are linked to diet. Whether you develop cancer depends on interactions between your diet, your genetic make-up and other risk factors. But there are things you can do to minimise the risk. How great a risk is, and whether you decide to minimise it will depend on other circumstances: whether it combines with other risks and who is benefiting from the risk, for example. If you are exposed to the risk but any party benefits from it (industry, say), you may feel differently about it, however small. Felicity Lawrence

1 When your lifestyle is a risk factor
The single largest contributor to cancer is smoking. While 90% of lung cancers are linked to smoking, scientific studies have also linked the disease to a lengthy list of other cancers, including larynx (voicebox), throat, oesophagus, bladder, kidney, pancreas, nasal cavity and sinuses, cervix and myeloid leukaemia. It is perhaps even less surprising then that half of all smokers die prematurely. Of these, a quarter die of lung cancer. It's not just smokers who are at a greater risk of lung cancer. A study of married couples where only one smoked showed the non-smoker had a 25% increase risk of lung cancer. Exposure in the workplace can raise the risk by 17%. Drinking alcohol also adds to your chances of developing certain types of cancer. Around half of all cancers of the mouth, throat and oesophagus are linked to heavy drinking. It has also been shown to increase the risk of breast cancer by up to 10%, but not all studies have repeated this finding.

Exercise has been shown to have some effect on reducing the cancer risk. Around 5% of all cancers in the EU might be prevented if no one was obese. Specific studies show that men who are highly active can halve their risk of developing colon cancer.

Some lifestyle factors have different effects of different cancers. Women who take oral contraceptives, for example, have a 24% increased risk of developing breast cancer, although the risk falls back to normal after 10 years of giving up the pill. However, contraceptive pills have been shown to decrease the risk of ovarian cancer by 40%.

Having children also affects things. For every birth, the risk of developing breast cancer has been shown to drop by 7%, while the risk of ovarian cancer dropped 16%. But another study found that women who had more than five children were twice as likely to develop kidney cancer, although the effect was more marked among obese women. Ian Sample

2 What goes into cosmetics can get into you
Put stuff on your skin or hair and it is likely that chemicals contained within it will get into your bodily tissues to some extent. Arguably the most studied cosmetic is permanent hair dye. Studies of women who used permanent hair dye at least once a month found they had a two-fold increase in the risk of developing bladder cancer compared with those who never used hair dye. Handling the dye puts hairdressers and barbers at particular risk - research shows those who have worked in the industry for 10 or more years are five times more likely to develop the disease. To put the risk in perspective, the chance of developing bladder cancer - which includes those who do and don't come into contact with hair dyes - is 3.3% for men and 1.3% for women.

The latest cosmetic cancer scare was sparked by research published this week by scientists at Reading University, who analysed tissue from breast tumours and found that 18 out of 20 samples contained chemicals called parabens, which are found in some cosmetics and deodorants. The scientists raised concerns because parabens have been shown to mimic the female hormone oestrogen, which can speed the growth of tumours. The research did not go as far as to check whether women with healthy breasts also had traces of parabens - a necessary step to show whether or not the absorbed parabens were causing tumours.

Another cosmetic that has fallen under the scientists' gaze is talcum powder. Some studies have shown that dabbing talc on the perineum can increase the risk of ovarian cancer. One of the most extensive studies found the risk increased by 33% (from a baseline risk of about 2% over a lifetime). But scientists are unclear how talc might raise the risk of ovarian cancer and other studies have failed to find a link. Ian Sample

3 Technology to die for is not a proven
If you live in a city and don't smoke, your biggest risk of developing cancer comes from air pollutants such as nitrogen dioxide or sulphur dioxide. Diesel fumes have also been linked with an increased risk of lung cancer. A study published last year looked at the association between incidence of lung cancer and long-term air pollution exposure in a group of Norwegian men followed from 1972 to 1998. They found that, out of 16,209 men, 418 had developed lung cancer. After controlling for age and smoking habits, they concluded that the excess risk (ie, the risk over and above that if there was no air pollution at all) was about 8%. Compared with your increased risk due to smoking, that's still relatively small.

Sunbathing is also linked to increased risk of cancer. According to Cancer Research UK, sunburn can increase the risk of melanoma. Recent research shows an average of 6.1 cases of melanoma in men and 7.7 in women per 100,000 people every year. This compares with a rate of 40.5 in men and 31.8 in women per 100,000 in Australia. There are many possible reasons for the increase in malignant melanomas, says Lars Jarup, a medical epidemiologist at Imperial College, London. "One is that people are commuting more on their holidays to nice sunny places."

Even sunbeds are thought to increase the risk: in the UK, melanomas from sunbed use cause about 100 deaths a year out of about 3-4 million users.

Another suspect is the number of synthetic chemicals that have been pumped into the environment over the past few centuries. Scientists estimate that there are up to 80,000 chemicals in use. And we have no idea what the long-term effects of most of them are. The European Union recently passed legislation to test them all to work out how toxic they all are; whether they increase our risk of cancer will need much more long-term research. Alok Jha

4 Dangers in the environment
There are lots of people who believe that mobile phones are slowly cooking our brains. Unfortunately for them (and fortunately for us), there is actually no scientific evidence to date which supports that claim. Laura Yochum, a cancer epidemiologist, conducted a review of the research into the effects of mobile phone radiation and concluded that regularly using a phone for up to five years does not cause cancer.

"The radiation (radio frequency signals) from cellphones is not strong enough to cause cancer directly by damaging DNA," says Yochum. "The energy from a RF wave is billions of times lower than the energy from an x-ray (high doses of x-rays do damage DNA). There is some evidence that RF causes other biologic effects, but no evidence that these effects will lead to disease or injury."

Similarly, mobile phone base stations are also given a clean bill of health, for now. "The radio frequency signal exposure from a cellular phone base station is many times lower than from using a cellphone and is well below international exposure guidelines," says Yochum. "On this basis, the independent review mentioned previously concluded the balance of evidence indicates there is no general risk to the health of people living close to base stations."

That doesn't mean that mobile users are off scott free. Just because there have been no proven links so far, does not mean that there are none and there are plenty questions still to be answered. As a result, the International Agency for Research on Cancer is coordinating a study in 13 countries to evaluate the effects of long-term mobile phone use. The first results of the study are expected later this year. Alok Jha

5 Five a day diet advice ignored
Diet has a huge effect on your chances of developing a range of cancers, including cancer of the bowel, stomach, mouth, throat and oesophagus. Diet is also suspected to play a role in cancer of the breast, pancreas, uterus, lung, bladder, kidney, prostate and liver.

Unsurprisingly, colon cancer is most strongly linked with diet and estimates suggest 80% of colon cancers would not occur if people improved their diets.

The mainstay of dietary advice is five different portions of fruit and vegetables - a portion being an apple, a cup of grapes or a couple of servings of green vegetables. The average person in the UK eats 2-3 portions of fruit and veg a day, less than half that consumed in the low-cancer rated Mediterranean.

According to Cancer Research UK, people who eat adequate amounts of fruit and veg can halve their risk of developing stomach cancer. Eating vegetables has been found to protect to some degree against lung cancer as well.

Experts warn that red meat consumption has been linked to a higher risk of colorectal cancer. The Food Standards Agency recommends no more than 90g of red or processed meat (the equivalent of two rashers of bacon and a sausage or a small doner kebab) a day.

Scientists remain divided on whether we should be eating Scottish farmed salmon in the light of research published in the journal Science. Sir John Krebs, chairman of the FSA, says the levels of contaminants fell within internationally recognised safe limits and that the benefits of eating the fish outweigh the cons.

Studies are contradictory. There is substantial evidence that foods rich in beta-carotene reduce the risk of lung cancer, yet a 12-year trial showed no benefit and two shorter trials actually showed an increased risk. Ian Sample