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Environment More Than Genetics May Increase The Risk For Cancer

A new study in today's New England Journal of Medicine says that environmental factors -- such as diet and smoking -- have more to do with your risk of getting cancer than your genetic makeup. The president of the American Red Cross and Early Show health contributor, Dr. Bernadine Healy talks about the study.

For decades scientists have been debating the causes of cancer--is it nature or nurture, and genetics or environment?

The gold standard for distinguishing genetic from environmental causes of cancer has been the study of twins. The New England Journal of Medicine study called "Environmental and Heritable Factors in the Causations of Cancer," examined records of twins from Sweden, Denmark, and Finland. The study concludes that environmental factors are the dominant factors in determining the risk of cancer (approximately 65% or more). The study concludes that there is a low probability that a cancer will develop in an identical twin, a person with an identical genome, has the same type of cancer. A few types of cancer were found to occur in both twins -- indicating genetic predisposition -- but the majority of cancer types occurred in only one twin -- suggesting environmental causes.

The study found genetic predisposition for prostate cancer, colorectal cancer, breast cancer, stomach cancer, and lung cancer in twins. Environmental causes were to blame for non-Hodgkin's lymphoma. Hodgkin's disease, lip cancers of the lip, oral cavity, pharynx, kidney, thyroid, bone and soft tissue affected only one twin in a pair.

In the past 15 years, the field of genetics has exploded and revealed genetic explanations for cancer. Researchers say it will be instructive to those that believe with enough information it will be possible to predict accurately who will contract a disease and who will not.

Another cancer researcher, Dr Mel Greaves, author of "Cancer: the Evolutionary Legacy" and director of Leukemia Research at the Institute of Cancer Research in London, England, has drawn a stronger conclusion than the twins study. Dr Greaves blames the environment for even more cancer, possibly up to 90%, and genetic makeup is only responsible for 10%. According to Greaves, in addition to toxic material and industrial pollutants, natural substances in food and changes in reproductive habits and our normal hormones also can cause cancers. The American Institute for Cancer Research (AICR) is on board with these conclusions, and since 1982, it has advocated the environment as cancer connection. They cite tobacco, diet, weight, physical activity, and work place exposures as environmental causes of cancer. To date, AICR states more than 4,500 diet-cancer studies have been completed. About a third of cancers are related to dietary factors. Results consistently find cancer-fighting benefits from diets high in fruits, vegetables, whole grains and beans. It's well known that there are health benefits in eating five servings of gree and yellow vegetables and fruit. Other substances have also been shown in animal studies to reduce cancers: tea, the herb rosemary, and the chemical which produces the yellow color in curry.

Dr Laurence Kolonel, a cancer researcher at the University of Hawaii, has studied Asian women and found that, in Asia, they have low rates of breast cancer. However, once these women move to the United States, their rates of breast cancer increase to match those of other American women. The theory of this result is directly linked to changes in diet. This is consistent with the findings in this study that 73% of the cause of breast cancer is environmental and 27% is genetics.



  2. Moderate amounts of alcohol have been shown to decrease the risk of coronary heart disease. But, the American Cancer Society says that cancer risk increases with more than two drinks a day. Th American Lung Association estimates that 87% of all lung cancer is caused by smoking.


  4. It is estimated that one-third annual cancer deaths are due to poor eating habits. The most effective dietary step to reduce cancer risk is to eat five or more servings of fruits and vegetables daily.


  6. Eating meat, poultry and fish that are grilled has been linked to an increased risk of cancer. There is no reason to eliminate grilled foods. But you should choose lean cuts of meat, use tongs instead of a fork to turn food (punctured meat will drip juices and cause the coals to smoke or flame, causing the formation of carcinogenic compounds. To avoid that you should partially cook meat in the oven or microwave before grilling to reduce exposure to smoke and flames.


  8. Skin cancer is the most commonly occurring form of cancer, out ranking all other cancers combined. To prevent exposure to the sun, wear long sleeve shirts, pants, sunglasses and a hat, avoid the sun between 10 am and 4 pm, and always wear sunscreen with at least SPF 15.


  10. Just about everyone can benefit from taking a multi vitamin every day.


  12. Studies confirm that people who are more active have lower rates of cancer and heart disease. Experts say that you should be active at least 30 minutes a day most of the days in a week.


  14. Regular screenings and self-exams can detect many cancers, but early detection is key to good outcome. When detected early, the survival rate for cancer patients can be as high as 92%.

Below are Dr. Healy's comments:

We've known for years that cancer is a complex interaction between genes and the environment. When we say environment we are talking about the external environment, things like tobacco. But we aralso talking about your internal environment, the environment within your body.

Environmental factors are broadly defined. They include external factors, such as tobacco, and sun exposure as well as behavioral factors such as diet, weight and physical activity. Then there are internal factors, such as age, reproductive history and infectious agents like STD's (which causes cervical cancer).

Cancer is a genetic disease. It is about genes misfiring and changing so that normal cells become cancerous cells. So the mapping of the human genome is a good thing. The underlying mechanism of cancer is at the genetic level, but it is not about genes you are born with.

It is good news that cancer is not all inherited. It means that we have the opportunity to modify and develop preventative schemes.

Lung cancer is at the top of every list. It's the number one killer. The vast majority of people dying from lung cancer would not have cancer if they had not smoked. And on top of it our young people are taking up smoking in droves.

Prostate cancer is most likely to be caused by genetic factors. Breast cancer is also largely genetic.

People should change what they can do sensibly. They should stick to a diet low in fat, high in fiber and eat 5 servings of fruits and vegetables a day. They should monitor their weight, increase physical activity, not smoke, avoid the sun and avoid sexually transmitted diseases (which are the cause of cervical cancer).

A little alcohol is ok, but avoid it in excess. Also, high-fat diets are thought to cause colon cancer and prostate cancer. It's been shown that 5 servings of fruits and vegetables a day dramatically decrease your risk of cancer.

We are told to eat broccoli, but watch out for pesticides, drink red wine, or don't drink red wine, stay out of the sun, but some sun is good. If we now know that environmental factors play a huge part in whether we get cancer or not, how are people supposed to sor through all these?

There are a lot of things we just don't know. The best we can do is everything in moderation and nothing in excess. We aren't sure if cell-phones cause cancer -- so don't walk around with a cell phone attached to your ear. Use common sense. It's important for people to know that not all cancer kills. Early detection is the key. If you live long enough, you have a pretty high chance of getting cancer, but the key is catching it early.

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