What you need to know about cancer risk factors

Although some cancer risk factors are inherited, genes are actually only responsible for 2-3% of all cancers, according to CANSA. Some risk factors are beyond your control - such as aging - while others, such as living a healthy lifestyle, are very much firmly in your hands. Here's a look at some scientifically-proven contributors to cancer.

Tobacco

According to the World Health Organisation, tobacco use is the single greatest avoidable risk factor for cancer mortality, killing approximately 6 million people each year from cancer and other conditions. People who use tobacco products or who are regularly around second-hand smoke have an increased risk of cancer due to the hundreds of chemicals contained in tobacco products that damage DNA. Tobacco use causes a myriad cancer types, including cancer of the lung, larynx (voice box), mouth, oesophagus, throat, bladder, kidney, liver, stomach, pancreas, colon and rectum, and cervix, as well as acute myeloid leukaemia.

Of the more than 7 000 chemicals in tobacco smoke, at least 250 are known to be harmful with at least 69 having the potential to cause cancer.

Age

Advancing age is another important risk factor. According to data from the US National Cancer Institute's Surveillance, Epidemiology and End Results Program, the median age of a cancer diagnosis is 66. This means that half of cancer cases occur in people below this age and half in people above this age. One-quarter of new cancer cases are diagnosed in people aged 65 to 74. There's a similar pattern for many common cancer types. For example, the median age at diagnosis is 61 years for breast cancer, 68 years for colorectal cancer, 70 years for lung cancer, and 66 years for prostate cancer. Of course, cancer can affect people at any life stage.

Alcohol

Drinking can increase your risk of cancer of the mouth, throat, oesophagus, larynx, liver, and breast. The more you drink, the higher your risk. The risk of cancer is much higher if you drink alcohol and also use tobacco. If you drink around three and a half drinks daily, you have at least a two to three times higher risk of developing these cancers than non-drinkers, according to a study published in Lancet Oncology.

Researchers have identified a number of ways that alcohol increases the risk of cancer, including metabolizing ethanol in alcoholic drinks to acetaldehyde, which is a toxic chemical and a likely human carcinogen as it can damage both DNA and proteins.

Chronic Inflammation

Inflammation is a normal healing process of the body. But in chronic inflammation, the inflammatory process starts even when there's no injury, and doesn't end. Chronic inflammation may be caused by persistent infections, abnormal immune reactions, or conditions such as obesity. Over time, chronic inflammation can cause DNA damage and lead to cancer. For example, people with chronic inflammatory bowel diseases, such as ulcerative colitis and Crohn's disease, have an increased risk of colon cancer.

Diet

According to CANSA, for the great majority of people who are not smokers, the most important modifiable determinants of cancer risk are weight control, levels of physical activity and dietary choices. “Only 5 to 10% of all cancers occur as a result of inherent genetic alterations,” says registered dietician Jeske Wellmann. “It’s estimated that one third of anticipated cancer deaths can be attributed to nutrition and lifestyle behaviours - poor diet, physical inactivity, alcohol and tobacco use and being overweight or obese. And, with the World Health Organisation (WHO) predicting a 70% increase in global cancer rates by 2035, the only way to achieve a good quality of life - and reduce your cancer risk - is by taking control of your lifestyle, with nutrition playing a central role.” Read more about this here.

Environmental pollutants

Cancer is caused by changes to certain genes that alter the way your cells work. Some of these genetic changes occur naturally when DNA is copied during cell division but others result from environmental exposures that damage DNA, such as the chemicals in tobacco smoke, or ultraviolet rays from the sun. You can avoid some cancer-causing exposures, such as tobacco smoke and the sun's rays. But others are not as easy to avoid, especially if they are in the air, water, food or materials used in building or mining. These toxins include arsenic (from smoking tobacco, drinking contaminated water), asbestos (in some building materials), benzene (found in some glues, cleaning products, and paint strippers, cigarette smoke, petrol fumes, and industrial emissions); formaldehyde (from exhaust pipes, wood-burning stoves, and kerosene heaters), and many others.

Hormones

Although oestrogens have an essential role in both female and male functioning, they've also been associated with an increased risk of certain cancers. For instance, taking combined menopausal hormone therapy (oestrogen plus progestin, which is a synthetic version of the female hormone progesterone) can increase your risk of breast cancer. Menopausal hormone therapy with oestrogen alone increases your risk of endometrial cancer so is only used in women who have had a hysterectomy. If you're considering hormone therapy, discuss the possible risks versus benefits with your doctor.

Immunosuppression

Immunosuppressive drugs make your immune system less able to detect and destroy cancer cells or fight off infections that cause cancer. Infection with HIV also weakens your immune system and increases your risk of certain cancers.

Transplant recipients, too, seem to be at increased risk of a number of different cancers, some due to infectious agents.

Infectious Agents

Viruses, bacteria, and parasites can cause cancer or increase your cancer risk. Some viruses can disrupt normal cell growth patterns. In addition, some infections weaken your immune system, making your body less effective at fighting off other cancer-causing infections. Most of the viruses that are linked to an increased risk of cancer can be passed from one person to another through blood and/or other body fluids. You can lower your risk of infection by getting vaccinated, not having unprotected sex and not sharing needles.

Obesity

People who are obese may have an increased risk of several types of cancer, including cancers of the breast (in women who have been through menopause), colon, rectal, endometrium (lining of the uterus), oesophagus, kidney, pancreas, and gallbladder. This may be due to a number of reasons. For example, obese people often have chronic low-level inflammation, which can, over time, cause DNA damage that leads to cancer, according to a study in the Annual Review of Immunology. Fatty adipose tissue produces excess oestrogen and obese people often have increased blood levels of insulin and insulin-like growth factor which may promote the development of colon, kidney, prostate, and endometrial cancers. Fat cells may also have effects on other cell growth regulators. Eating a healthy diet, exercising regularly, and maintaining a healthy weight helps to reduce your risk of some cancers.

Radiation

Radiation of certain wavelengths has enough energy to damage DNA and cause cancer. Ionizing radiation includes radon, x-rays, CT scans, gamma rays, and other forms of high-energy radiation. The risks of cancer from medical x-ray procedures are very small, and the benefit from having them is almost always greater than the risks. Lower-energy, non-ionizing forms of radiation, such as visible light and the energy from cell phones has not been found to cause cancer.

Sunlight

Find out more about the links between exposure to sunlight and cancer here.