moking lowers the risk of getting cancer and dying from cancer. Scientists believe that cigarette smoking causes about 30 percent of all cancer deaths in the United States.
Certain viruses and bacteria are able to cause cancer. Viruses and other infection -causing agents cause more cases of cancer in the developing world (about 1 in 4 cases of cancer) than in developed nations (less than 1 in 10 cases of cancer). Examples of cancer-causing viruses and bacteria include:
Human papillomavirus (HPV) increases the risk for cancers of the cervix, penis, vagina, anus, and oropharynx.
Hepatitis B and hepatitis C viruses increase the risk for liver cancer.
Epstein-Barr virus increases the risk for Burkitt lymphoma.
Helicobacter pylori increases the risk for gastric cancer.
Two vaccines to prevent infection by cancer-causing agents have already been developed and approved by the U.S. Food and Drug Administration (FDA). One is a vaccine to prevent infection with hepatitis B virus. The other protects against infection with strains of human papillomavirus (HPV) that cause cervical cancer. Scientists continue to work on vaccines against infections that cause cancer.
Radiation. Being exposed to radiation is a known cause of cancer. There are two main types of radiation linked with an increased risk for cancer:
Ultraviolet radiation from sunlight: This is the main cause of nonmelanoma skin cancers.
Ionizing radiation including: Medical radiation from tests to diagnose cancer such as x-rays, CT scans, fluoroscopy, and nuclear medicine scans. The risk of cancer after being exposed to ionizing radiation from diagnostic x-rays is higher for younger age groups than for older age groups, and is higher for women than for men. The risk of cancer also increases with the number of diagnostic x-rays a patient is given and the radiation dose per x-ray.
Radon gas in our homes. Scientists believe that ionizing radiation causes leukemia, thyroid cancer, and breast cancer in women. Ionizing radiation may also be linked to myeloma and cancers of the lung, stomach, colon, esophagus, bladder, and ovary. Being exposed to radiation from diagnostic x-rays increases the risk of cancer in patients and x-ray technicians.
Diet. The foods that you eat on a regular basis make up your diet. Diet is being studied as a risk factor for cancer. It is hard to study the effects of diet on cancer because a person’s diet includes foods that may protect against cancer and foods that may increase the risk of cancer.
It is also hard for people who take part in the studies to keep track of what they eat over a long period of time. This may explain why studies have different results about how diet affects the risk of cancer.
Some studies show that fruits and non-starchy vegetables may protect against cancers of the mouth, esophagus, and stomach. Fruits may also protect against lung cancer.
Some studies have shown that a diet high in fat, proteins, calories, and red meat increases the risk of colorectal cancer, but other studies have not shown this.
It is not known if a diet low in fat and high in fiber, fruits, and vegetables lowers the risk of colorectal cancer.
Studies have shown that drinking alcohol is linked to an increased risk of the following types of cancers:
Drinking alcohol may also increase the risk of liver cancer and female colorectal cancer.
Exercise. Studies show that people who are physically active have a lower risk of certain cancers than those who are not. It is not known if physical activity itself is the reason for this.
Studies show a strong link between physical activity and a lower risk of colorectal cancer. Some studies show that physical activity protects against postmenopausal breast cancer and endometrial cancer.
Obesity. Studies show that obesity is linked to a higher risk of the following types of cancer:
Some studies show that obesity is also a risk factor for cancer of the gallbladder.
Studies do not show that losing weight lowers the risk of cancers that have been linked to obesity.
Chemicals and Other Substances. Being exposed to chemicals and