12 April 2011

Cancer risks: truth and myth

From Facebook and power lines to deodorants and pesticides, the world is allegedly teeming with cancer-causing agents. Which are real and which are urban legend?


From Facebook and power lines to deodorants and pesticides, the world is allegedly teeming with cancer-causing agents. Which substances should we really be worried about, and which are just scare stories?

Before we start separating the wheat from the chaff, it should be noted that cancer risk is highly dependent on dosage. A little sun exposure for example may be harmless, but a few bad burns and your risk of developing skin cancer shoots up dramatically.

Differences in dosage are also behind a lot of quietly interesting study findings being turned into untruths by headline-making stories. High doses of a substance may have encouraged tumour development in rats, but it doesn't follow that incidental doses will do the same in humans.

The known baddies
The evidence for some risk factors are rock-solid.

Smoking: The number one cause of cancer, smoking dwarfs other risk factors in its severity. Up to 90% of lung cancers are due to smoking and a number of other cancers have also been strongly linked to the addiction. The World Health Organisation (WHO) estimates that 5.4 million people die every year of smoking-related diseases.

Alcohol: Alcohol has been linked to an increased risk of developing mouth, throat, and oesophageal cancers. Recent studies have also suggested that alcohol ups the risk of developing breast cancer. As a general rule, the risk seems to increase the more alcohol you drink.

Sun exposure: Sun exposure is the single biggest controllable risk factor for skin cancer, and in South Africa we are at particularly high risk. Some studies have suggested that only a few bad burns could cause a major spike in your risk.

Lack of exercise: A number of studies have linked lack of physical activity to an increased risk of developing bowel cancer. In addition, women who exercise regularly have been shown to be at a reduced risk of developing breast cancer. Similar effects are suspected for a range of other cancers.

Overblown scare stories
The evidence supporting some supposed risk factors is severely thin, or may in fact have been discredited. This does of course not prevent them from landing in your inbox, or being splashed on the front page of your local tabloid.

Deodorants: An email claiming that deodorants cause breast cancer has been doing the rounds for a number of years. The email makes some far-fetched claims that are obviously inaccurate. Yet, scientists have taken the trouble to investigate the possibility of a link and a large study published in 2002 found that there is no link.

Power lines: Power lines, or the electromagnetic fields (EMF) around power lines, have not been shown to cause cancer in adults. An association has been found between childhood leukaemia and EMF, but we don't know if the EMF is to blame or whether a third factor might be at play. In any case, power lines would account for only a very small percentage of leukaemia cases. According to Cancer Research UK some experts believe that power lines would only cause about two cases of childhood leukaemia each year, if any. In contrast, smoking caused 46 000 UK deaths from a variety of cancers in 2002 alone.

Facebook: Recent headlines proclaimed that using the social network Facebook could raise your risk of developing cancer. In fact, the article that the furore was based on was an opinion piece, and not an actual study. Furthermore, critics have illustrated how the author cherry-picked findings to suit his hypothesis.

Pesticides: There is no evidence that the extremely small traces found on some fruits and vegetables hold any danger, says Cancer Research UK. There is, however, a suggestion that people exposed to large quantities of pesticides – in agriculture for example – may face a slightly increased risk of developing leukaemias or lymphomas.

Please note that this list is in no way a definitive list of cancer-causing agents or otherwise.

(Marcus Low, Health24, March 2009)

The main source for this article was Cancer Research UK's extensive resource on cancer risk and particularly their highly-informative "How do we know" sections.

Read more:
Check your cancer risk with this quiz.
Cell phone/cancer verdict


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