Cancer and the Environment : Part 2

by National Cancer Institute

(Page 2 of 5)

Hyperactive Detoxifying Activities

Other genes in the body produce detoxifying proteins that prepare toxic molecules for quick removal. Again, genetic variation in genes for detoxifying proteins can result in differences from one person to another in the ability to eliminate cancer-causing compounds. On the other hand, some genetic variation may actually produce hyperactive detoxifying gene activity. Then a person who possesses hyperactive detoxifying proteins may have some protection from harmful environmental exposures. Scientists believe, for example, that some persons inherit genes for hyperactive detoxifier proteins in lung tissues. This inheritance may partly explain why some smokers who refuse to give up the habit can still remain free of cancer. (For more information, please see Genetic Variation.)

Chance of Cancer? It Depends ...

We know that some exposures increase the risk of cancer, but we don't know which specific combinations of environmental factors on the outside of the body combine with gene changes on the inside to lead to cancer. We don't know why two persons can have very similar environmental exposures, yet one gets cancer and the other does not. A number of individual factors are involved and there are complex relationships among them.

The individual chance that someone will develop cancer in response to a particular, single environmental exposure depends on how long and how often that person was exposed. It also depends on the person's:

• exposures to certain environmental factors (including diet, hormones)
• genetic makeup
• age and gender

Environmental Carcinogens: The "Nasties" Lineup

Every two years, the Federal Government publishes a report on environmental exposures that have been linked to cancer. The most recent report included more than 220 substances. It helps to understand which of these exposures have the most impact on the general public.

As you consider these factors one at a time, it is important to remember that an individual accumulates a unique set of responses to his or her unique environment over a lifetime. Lengths and strengths of exposures will vary, and the person's genome itself will change.

Tobacco

Cigarette, cigar, and pipe smoking have been linked to more than a dozen types of cancer, including lung, mouth, bladder, colon, and kidney cancers. Chewing tobacco and snuff increase the risk of oral cancer, and second-hand smoke increases the risk of lung cancer.

Tobacco and Cancer Risks

Smoking is the single most common cause of cancer, and exposure to cancer-causing substances in tobacco products accounts for about 30 percent of cancer deaths in the United States. To reduce your cancer risk, don't smoke or use tobacco products. Avoid smoke-filled rooms if possible.

Alcohol

Alcohol is another risk factor. Heavy drinkers have an increased risk of cancers of the mouth, throat, liver, voice box, and esophagus. There is also some evidence for an increased risk of breast cancer. Drinkers who also smoke may have an even higher risk of some oral and throat cancers. Drink in moderation, if at all: no more than one or two drinks per day.

Overweight and Exercise

Being overweight is an important lifestyle factor related to cancer risk. There are links between obesity and the risks of breast cancer (in older women), endometrial cancer, and cancers of the kidney, colon, and esophagus. Not being physically active increases the risk of colorectal and breast cancers.

Together, obesity and physical inactivity are linked to about 30 percent of the cases of colon, endometrial, kidney, and esophageal cancers, as well as 30 percent of breast cancers in older women.

Losing weight and exercising can help reduce your risk. Exercise at least 30 minutes a day, most days of the week. Exercise alone can decrease the risk of colon cancer and breast cancer. The goal should be for adults age 20 or older to keep their Body Mass Index (BMI) below 25. The BMI is a number that shows your body weight adjusted for your height.

Diet

The federal report on carcinogens doesn't discuss specific foods and cancer risk. However, studies show that consuming large quantities of red meat, preserved meats, salt-preserved meats, and salt probably increases the risk of stomach and colorectal cancers. Research also shows that a diet high in fruits and vegetables may decrease the risks of these cancers. And calorie restriction has been shown to reduce cancer risk for several cancer types.

Eat a healthy calorie-restricted diet rich in whole grains, fruits, and vegetables. Avoid consuming large amounts of fatty foods, red meats, salt, or salt-preserved food.

Viruses

Some viruses are risk factors for cancer.

Human Papillomavirus

Certain strains of human papillomavirus (HPV), which are sexually transmitted, are the primary causes of cervical and anal cancer. Women who begin having sexual intercourse before age 17, or who have multiple sexual partners, are at greatest risk of HPV infection.

HPV may also be responsible for some cancers of the head and neck.

It's important to note that most people infected with HPV will not get cancer. Also, a vaccine is now available that can prevent infection with the strains of HPV that cause cervical cancer.

Hepatitis B and C

The hepatitis B and hepatitis C viruses are major causes of liver cancer worldwide. The viruses are transmitted through blood transfusions, injectable drug use, and unprotected sex. Vaccinations can protect against hepatitis B, but there is not yet a vaccine for hepatitis C.

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