Cancers can be caused by a number of different factors and, as with many other illnesses, most cancers are the result of exposure to a number of different causal factors. It is important to remember that, while some factors cannot be modified, around one third of cancer cases can be prevented by reducing behavioural and dietary risks.
Modifiable risk factors include:
- Alcohol– The evidence that all types of alcoholic drinks are a cause of a number of cancers is now stronger than ever before. Alcohol can increase the risk of six types of cancers, including bowel (colorectal), breast, mouth, pharynx and larynx (mouth and throat), oesophageal, liver and stomach.The evidence suggests that in general, the most alcohol drinks people consume the higher the risk of many cancers, and that even moderate alcohol intake increases the risk of cancer.
- Being overweight or obese – excess weight has been linked to an increased risk of developing 12 different cancers, including bowl and pancreatic cancers. In general, greater weight gain, particularly as adults, is associated with greater cancer risks.
- Diet and nutrition– Experts suggest that diets and nutritional intake, particularly diets high in red meats, processed meats, salted foods and low in fruits and vegetables have an impact on cancer risks, particularly colorectum, nasopharynx and stomach,,.
- Physical activity– regular physical activity not only helps to reduce excess body fat and the cancer risks associated with this, but being physically active can help to reduce the risks of developing colon, breast and endometrial cancers.
- Tobacco– Tobacco smoke contains at least 80 different cancer-causing substances (carcinogenic agents). When smoke is inhaled the chemicals enter the lungs, pass into the blood stream and are transported throughout the body. This is why smoking or chewing tobacco not only causes lung and mouth cancers but is also related to many other cancers. The more a person smokes, the younger they start, and the longer they keep smoking, all further increase the risk of cancer. Currently tobacco use is responsible for around 22% of cancer deaths.
- Ionising radiation– Manmade sources of radiation can cause cancer and are a risk for workers. These include radon, x-rays, gamma rays and other forms of high-energy radiation. Prolonged and unprotected exposure to ultraviolet radiations from the sun, sunlamps and tanning beds can also lead to melanoma and skin malignancies. Fair skinned people, individuals with a lot of moles or who have a family history of melanoma or non-melanoma skin cancer, are at highest risk. However, people of all skin tones can develop skin cancer, including individuals with darker skin.
- Work place hazards– Some people risk being exposed to a cancer-causing substance because of the work that they do. For example, workers in the chemical dye industry have been found to have a higher incidence than normal of bladder cancer. Asbestos is a well-known workplace cause of cancer – particularly a cancer called mesothelioma, which most commonly affects the covering of the lungs.
- Infection– Infectious agents are responsible for around 2.2 million cancer deaths annually. This does not mean that these cancers can be caught like an infection; rather the virus can cause changes in cells that make them more likely to become cancerous.
Around 70% of cervical cancers are caused by Human papillomavirus (HPV) infections, while liver cancer and Non-Hodgkin Lymphoma can be caused by the Hepatitis B and C virus, and lymphomas are linked to the Epstein-Barr virus.
Bacterial infections have not been thought of as cancer-causing agents in the past, but more recent studies have shown that people who have helicobacter pylori infection of their stomach develop inflammation of the stomach lining, which increases the risk of stomach cancer.