Move over, bacon - lots of other things cause cancer
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The agency also found that red meat (beef, lamb, etc.) may increase your risk of developing the same type of cancer.
Colorectal cancer is the third-most common type of cancer in the US, according to the American Cancer Society.
Americans have a 1 in 20 chance of developing it within their lifetime, and the disease is expected to cause about 49,000 deaths this year.
So, how does eating bacon and other deliciously salty processed meats shape up in terms of overall cancer risk?
Here's a list developed by the WHO of the leading carcinogens. Research shows you can reduce your risk of developing cancer by avoiding these:
Tobacco
Tobacco use, of any kind, accounts for 22% of cancer-causing deaths each year. That's about 1.4 million for the year 2004, the WHO estimates.
In part, that's because of the many different types of cancer tobacco use can cause, including mouth, throat, kidney, bladder, pancreas, and lung cancer.
And cancer isn't the only risk that comes with using tobacco. Right now 16 million Americans are living with a disease caused by smoking, according to the CDC.
Alcohol
Based on a number of studies, the more alcohol a person drinks regularly over time, the higher her risk of developing one of these alcohol-associated cancers. About 3.5% of all cancer-related deaths in the US in 2009 were alcohol-related.
What's more, out of all mouth and oropharn cancers, about 22% are attributable to alcohol use in men; about 9% of those cancers are attributable to alcohol use in women.
Excessive alcohol use can be deadly in other ways, too - the WHO estimates that each year 2.5 million deaths are associated with alcohol consumption, and 320,000 of those deaths are people between the ages of 15 and 29.
Radiation
Ultra-violet radiation from the sun, X-ray radiation from certain medical equipment, and exposure to radioactive elements like radon gas are all examples of ionizing radiation.
But the second leading cause of lung cancer after tobacco smoke is exposure to radon gas from soil and building materials. The WHO estimates that between 3 to 14% of all lung cancers are caused by exposure to radon gas.
According to the US Nuclear Regulation Commission, anyone exposed to 5,000 millisieverts or greater at one time will likely die without medical treatment. For comparison, you get about 10 millisieverts from one Computed Tomography (CT)-abdomen and pelvis test.
In high doses, ionizing radiation can cause life-threatening cancers like leukaemia and solid tumors. However, it is difficult to assess how many people die of radiation-related cancer each year because so few people are exposed to life-threatening levels.
Learn more about how much radiation you receive from different medical exams on RadiologyInof.org.
Infections
Sometimes, cancer can be caused by infections with viruses, bacteria, or parasites. Nearly 22% of cancer deaths in developing countries and 6% in industrialized countries are due to infectious diseases, according to the WHO.
For example, viral hepatitis B and C can cause liver cancer, while the sexually transmitted human papillomavirus (HPV, pictured above) can cause cervical cancer. Also, the bacterium Helicobacter pylori (which causes stomach ulcers) can increase the risk of stomach cancer. Parasitic infections like schistosomiasis, a parasitic disease carried by snails, and liver fluke, a parasitic flatworm that lives in the liver, have also been found to cause cancer.
Even though infections can increase a person's risk of getting cancer, most people don't end up getting them, according to the American Cancer Society. Getting vaccinated and avoiding infections are the best protection, but diet and other factors also play an important role.
Pollution
Air, water and soil pollution also have a role in causing cancer. The WHO reports that 1% to 4% of cancers are caused by carcinogens from drinking water or polluted air.
For example, diesel exhaust contains harmful gases and soot that have been linked to cancer in both humans and animals, especially lung cancer.
But often, the worst pollution is found indoors. Smoke from coal fires doubles the risk of lung cancer, especially in women who don't smoke, and is responsible for 1.5% of lung cancer deaths worldwide, according to the WHO.
And it's not just air pollution. In a part of Bangladesh contaminated with arsenic, a naturally occuring element that is toxic to humans, 5% to 10% of cancer deaths were linked to the toxic chemical.
Work hazards
Many people are exposed to carcinogens at work. There are more than 40 known substances found in work environments that are known to cause cancer of the lung, bladder, larynx (throat), and skin, as well as leukemia and nasopharyngeal cancer.
For example, asbestos, a well-known carcinogen, causes lung cancer and mesothelioma, a rare cancer of the outer lining of the lung or chest cavity.
And tetrachlorethylene (perchloroethylene), a substance used in dry cleaning, has also been found to be carcinogenic.
About 20% to 30% men and 5% to 20% of women (of working-age) may have been exposed to lung carcinogens during their careers, according to the WHO. That's about 10% of lung cancers worldwide.
Physical activity and diet
The WHO states that diets high in fruits and vegetables "may have a protective effect against many cancers," while diets high in red and processed meat come with a greater risk of colorectal cancer.
However, when it comes to the types of foods you eat, cancer should be low on your list of worries. Yes, you should be aware of what you put into your body, but how much you put in should be number one on your radar.
That's because obesity is linked to cardiovascular diseases like stroke and heart disease, which were the leading causes of death worldwide in 2012, according to the WHO.
In the US alone, 610,000 people die of heart disease each year - that's 12 times more than the people expected to die of colorectal cancer this year.