Environmental Factors & Lifestyle

Radiation

Melanoma: Australia's National Cancer

In today’s society, we are constantly exposed to radiation – all we have to do is step outside. UV radiation (in particular UVB) is one of the leading causes for melanoma, a form of skin cancer. Partly due to the hole in the ozone layer, Australia has the highest incidence of melanoma in the world.

On average, 30 Australians will be diagnosed with melanoma every day and more than 1,200 will die from the disease each year. — Melanoma Institute Australia

UV radiation disrupts bonds in DNA, increasing the incidence of mutations and DNA damage. In 2010, researchers at The Wellcome Trust Sanger Institute (Hinxton, UK), sequenced the genomes of both normal and melanoma tissues. After comparison, they were able to pinpoint where each mutation occurred, many of the 33000 mutations were found to have a ‘UV exposure imprint’. As Professor Mike Stratton explains, “We can see the desperate attempts of our genome to defend itself against the damage from ultraviolet radiation. Our cells fight back furiously to repair the damage, but frequently lose that fight.”

The danger of UV radiation has been underlined by the Cancer Council, whose ‘slip slop slap’ campaign is a mantra for many Australians. Sunscreens works by ‘filtering’ sunlight, preventing a significant percentage of UVB radiation from contacting and damaging our skin. This is indicated by the SPF – Sun Protection Factor, e.g. SPF 50+ filters 98% of UVB radiation.

Bombs

At 8:15am on August 15, 1945, an American bomber dropped an atomic bomb on Hiroshima. Sourced to a vessel of only 3m long, the explosion yielded approximately 200 radioactive isotopes, which ultimately caused the destruction of a city and its people. The radiation took a visible form of ‘black rain’, which stained skin and buildings. It entered bodies by breathing in the toxic air and via ingestion, as food and water were also contaminated. The initial ionising radiation was followed by residual radiation that lingered for some time after.

Whilst 60 000 to 80 000 people were killed instantly, 90% of medical personnel also died or were severely injured (Source), leaving the city in further desperation. However, of those that physically survived the bomb that day, thousands succumbed to the acute and long-term effects of radiation. By November 1945, the death count was 130 000.

Depending on their vicinity to the bomb and therefore, dosage of radiation, citizens suffered from acute radiation illness, with symptoms, including hair loss, anaemia, loss of white blood cells and bleeding. However, people are still suffering from the effects of the radiation today. In addition to disfiguring physical injuries, such as keloids, higher incidence of leukaemia and cancers of the thyroid, breast and lungs have been found in those exposed to the radiation. The radiation also affected the unborn generation, causing abortions and abnormal births.

The acute and long-term effects of radiation are also evident in nuclear power plant disasters, such as Chernobyl and more recently, Fukushima. Energy from nuclear power plants is generated from the decay of radioactive isotopes. These molecules are unstable and their breakdown results in the formation of other radioactive isotopes as well as ionising radiation.

Do mobile phones cause cancer?

This issue weaves in and out of media headlines, causing warranted public concern – after all rates of mobile phone usage has grown exponentially. Mobile phones emits radio frequency (RF) waves, a non-ionising form of electromagnetic (EM) radiation. RF waves have a low frequency, differing from high frequency ionising EM waves, which include x-rays, gamma rays and UV radiation. So the question is – are RF waves capable of causing DNA damage like that of ionising radiation?

Research groups have conducted different studies to tackle this issue. These range from: exposing human cells in the lab to RF waves to epidemiological studies – seeing if there is a link between mobile phone usage and brain cancers in the human population.

So, what’s the consensus? Currently, the research suggests that mobile phones are unlikely to increase the risk of brain cancer. Although some studies have found small links between the two variables, issues with the study design cloud the results. As research remains ongoing, it is important to note that not enough is known to completely rule out mobile phones as a source of cancer-causing radiation.

Other sources of radiation may be sourced to medical centres, where patients are exposed to x-rays, gamma rays (in PET scans), and radioactive isotopes in cancer treatment.

Smoking

Of the 7000 chemicals in tobacco smoke, at least 70 are known carcinogens. According to Cancer Council Australia, smoking is responsible for 20% of cancer deaths in Australia and accounts for 80% of lung cancers. The list of cancers that smoking also causes is seemingly endless.

Smoking also causes cancer of the tongue, mouth, throat, nose, nasal sinus, voice box, oesophagus pancreas, stomach, liver, kidney, bladder, ureter, bowel, cervix, ovary, and bone marrow (myeloid leukemia). — Quit

Each cigarette causes DNA damage, particularly in the p53 gene.

Research has shown that for every 15 cigarettes smoked there is a DNA change which could cause a cell to become cancerous. — Cancer Research UK

DNA and cellular damage can be further amplified by the accumulation of toxins and toxic radicals. Chemicals in cigarette smoke can overwhelm ‘detoxification’ enzymes, which convert toxic chemicals into harmless ones. Smoking also destroys cilia, small hairs on cells lining airways that remove toxins from the lungs.

Impaired function of cilia (slower "beat frequency," i.e. the cilia are not moving as fast as they should be), and/or a change in the properties of nasal mucus, are associated with an increase in bacterial colonisation and infection. Thus, smokers have an increased risk of recurrent infection, particularly by Streptococcus pneumoniae, a known causative agent of bacterial pneumonia.

Carcinogens in cigarette smoke also work by changing our immune system. Some chemicals may activate cells that promote tumour growth and inhibit cells that suppress or kill cancer cells.

What about passive smoking?

Second hand smoke can also increase a non-smoker’s risk of cancer. According to Cancer Council Australia, a 2004 study found that in one year, 600 000 deaths worldwide were attributed to passive smoking.

Cured Meats

A significant amount of research now supports the notion that processed meat and red meat enhances the risk of bowel cancer. Processed meat is defined as meat that has been ‘cured, salted, smoked, or otherwise preserved in some way (so things like bacon, sausages, hot dogs, ham, salami, and pepperoni)’, whilst red meats include beef and lamb. According to Cancer Council Australia, data from the 1995 National Nutrition Survey (the most recent nutrition survey to date) shows that red meat attributes to 8% towards the risk for bowel cancer, whilst processed meat contributes 7.5%. More recently, the World Cancer Research Fund estimated that in the UK, high consumption of red meat and processed meat accounts for 5% and 10% of bowel cancers respectively.

However, researchers are still not sure how meat causes cancer. Some believe cancer growth is promoted by preservative chemicals or by the nitrogenous compounds found in meat. Others postulate that high levels of iron may cause the production of radicals that then cause cellular and DNA damage. Nevertheless, in light of the research, Cancer Council Australia recommends:

• Having a moderate consumption of unprocessed red meats (65-100g, 3-4 times a week)

• Avoiding processed meat

• Avoiding charred meats

• Choosing lean cuts of meats and chicken, and eating more fish

Asbestos

Asbestos was commonly used in industry due to its non-conductive nature and resistance to high temperatures, humidity and chemicals. Exposure to asbestos came in many forms, particularly through work (mining, installation of materials in buildings, electricians, plumbers etc.) and via interaction with material lined with asbestos, such as washing clothes. It is now understood that asbestos is a carcinogen. When fibres are breathed in, they may settle or be trapped in the lungs. This accumulation can then cause inflammation and scarring of the lungs, a process that occurs over decades. It is due to this latency period that effects of asbestos have only become apparent in the recent decade. Studies indicate that asbestos is the primary cause of mesothelioma, a cancer of thin membranes including those that line the lungs (known as pleura) and abdomen (called the perineum). According to Cancer Council Victoria (2015):

Australia has one of the highest rates of mesothelioma in the world. According to the Australian Mesothelioma Registry, each year close to 600 Australians are diagnosed with pleural mesothelioma. Men are over three times more likely than women to be diagnosed with pleural mesothelioma. This is probably because many cases have been caused by exposure to asbestos at work. — Cancer Council Victoria, 2015

Asbestos also increases the risk to developing lung cancer. Interestingly, the National Cancer Institute noted that the combination of smoking of asbestos elevates the risk of lung cancer to a level that is greater than the sum of the individual risks of asbestos and smoking.

Viral Infections

According to the Yale Journal of Biology and Medicine, about 15% of known human cancers can be attributed to viruses. Cancer-causing viruses, including Human Papilloma Virus (HPV), Epstein Barr Virus (EBV), Hepatitis B and Hepatitis C, differ in their genomes and lifecycles. Only a small percentage of infected individuals develop cancer and its formation is generally quite slow – arising years or decades after the primary infection. It is important to note that a viral infection is not enough to cause cancer. Host factors also play a role for cancer formation; they include genes that are involved with immune function, immunosuppression and exposure to carcinogens.

Whilst EBV causes a wide range of human cancers, Hepatitis B and C infections can result in hepatocellular carcinoma, the most common form of liver cancer. On the other hand, HPV predominantly causes cervical cancers. The virus integrates its DNA into human DNA in healthy cells and uses the cell’s machinery to make two harmful viral proteins, E6 & E7. These proteins bind to tumour suppressor proteins – p53 and Rb (retinoblastoma). This means that cells growth is unregulated – the beginning of cervical cancer formation. Currently, “cervical cancer is the second leading cause of cancer mortality in women worldwide, causing 240,000 deaths annually.”