Factors Contributing to Cancer
Eighty percent of cancers are due to factors that have been identified and can potentially be controlled, according to the National Cancer Institute. And not only can we potentially prevent most cancers, we can also improve the survival rates of people who have cancer. Cancers of the breast, prostate, and colon have received more research attention than other forms of the disease, but, as we will see, certain principles apply to many forms of cancer.
Cancer starts when one cell begins to multiply out of control. It begins to expand into a lump that can invade healthy tissues and spread to other parts of the body. But there is a lot we can do about it. Thirty percent of cancers are caused by tobacco. Lung cancer is the most obvious example, but by no means the only one. Cancers of the mouth, throat, kidney, and bladder are also caused by tobacco.
Dietary factors also play a significant role in cancer risk. At least one-third of annual cancer deaths in the United States are due to dietary factors.1 A review on diet and cancer estimates that up to 80 percent of cancers of the large bowel, breast, and prostate are due to dietary factors.1
In 2008, excess body weight was responsible for over 124,000 new cancer diagnoses in Europe. These results were presented at a major European cancer conference in 2009 and showed endometrial (uterine) cancer, postmenopausal breast cancer, and colorectal cancer were the most common weight-related cancers. These three cancer types accounted for 65 percent of all cancers due to excess body weight. The effects of obesity also appear to increase mortality from several other types of cancer including gallbladder, pancreas, kidney, cervix, and ovary, as well as non-Hodgkin’s lymphoma in women with the highest BMIs compared to those with a healthy BMI.2 Previous studies including the Adventist Health Study-2 show that following a vegan diet results in the lowest BMI of any group (lacto-ovo-vegetarian, pesco-vegetarian, semivegetarian, nonvegetarian), making them less susceptible to obesity-related cancers.3
The link between diet and cancer is not new. In January 1892, Scientific American printed the observation that "cancer is most frequent among those branches of the human race where carnivorous habits prevail." Numerous research studies have shown that cancer is much more common in populations consuming diets rich in fatty foods, particularly meat, and much less common in countries eating diets rich in grains, vegetables, and fruits. One reason is that foods affect the action of hormones in the body. They also affect the strength of the immune system and other factors. While fruits and vegetables contain a variety of vitamins, minerals, antioxidants, and phytochemicals to protect the body, by contrast, recent research shows that animal products contain potentially carcinogenic compounds which may contribute to increased cancer risk.5
In addition to tobacco use and diet, other factors, including physical activity, reproductive and sexual behavior,4 bacterial and viral infections, and exposure to radiation and chemicals, may also contribute to the risk of certain forms of cancer.4,6
Estimated Percentages of Cancer Due to Selected Factors5,6
|Diet||35% to 60%|
|Air and Water Pollution||5%|
1. American Cancer Society. Cancer Facts and Figures—1997. Atlanta, GA: 1999.
2. Renehan A. Obesity and overall cancer risk. Presented at the Joint ECCO 15-34th ESMO Multidisciplinary Congress. Berlin, Germany, September 20-24, 2009. Abstract I-327.
3. Tonstad S, Butler T, Yan R, Fraser GE. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care. 2009;32:791-796.
4. Minamoto T, Mai M, Ronai Z. Environmental factors as regulators and effectors of multistep carcinogenesis. Carcinogenesis. 1999;20(4):519-527.
5. Skog KI, Johansson MAE, Jagerstad MI. Carcinogenic heterocyclic amines in model systems and cooked foods: a review on formation, occurrence, and intake. Food and Chem Toxicol. 1998;36:879-896.
6. Cummings JH, Bingham SA. Diet and the prevention of cancer. BMJ. 1998;317:1636-1640.