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Cancer risk can be cut with good habits such as exercise and healthful eating

By Ranit Mishori
Special to The Washington Post
Monday, September 27, 2010; 6:35 PM

There was a time when "cancer" was a word that was only whispered in polite society. It was the devastating, invidious illness that almost nothing could be done about. Death from cancer was ugly, unavoidable and best not thought about until you absolutely had to. Preventing it was thought to be, in most cases, out of the realm of possibility.

Today, we know a great deal more about cancer and have made advances in its treatment. Yet many of us are still in denial, reluctant to engage the topic in our daily lives.

In fact, there are a number of common-sense ways to reduce your risk of getting certain kinds of cancer. No guarantees, but there are steps you can take now to improve your odds.

And guess what? They're the same things you do to avoid getting heart disease. That's right: Watching your weight, avoiding junk food and getting exercise - which you already knew will would help to fend off a heart attack - also greatly reduce your chances of getting cancer.

According to the American Cancer Society, about a third of the 550,000 American cancer deaths each year are linked to obesity, poor diet and inactivity. Another third are due to smoking.

In other words, one of the biggest contributors to cancer risk is lifestyle - and that's something over which you have control.

The numbers behind this statement? "Forty percent of breast cancer cases in the U.S. - about 70,000 cases a year - could be prevented" by changes in behavior, says Susan Higginbotham, director of research for the American Institute of Cancer Research.

A German study published last year in the Archives of Internal Medicine showed a 36 percent reduction in cancer risk overall among people who changed to more-healthful habits. A Harvard School of Public Health study described 44 percent of cancer deaths as avoidable in a report that appeared in BMJ, a British medical journal.

None of this is easy, but bad habits can be changed, and it's good to know which ones count when it comes to reducing your risk of cancer. So here they are:

Obesity

More than 100,000 cancer cases each year - cancers of the uterus, esophagus, pancreas, kidney, gallbladder, breast and colon - are linked to being overweight, according to the AICR. Scientists believe it partly has something to do with estrogen stored in and produced by our fat cells.

In women, "fat cells are a major source of estrogen after menopause," says Michael Thun, vice president emeritus of epidemiology and surveillance at the American Cancer Society. That estrogen, he notes, "promotes the development of uterine and breast cancer."

Fat also increases the concentration of a substance called insulin-like growth factor, which has also been linked to cancer. Furthermore, recent studies have looked at chronic inflammation - to which obesity contributes - and its role in various cancers, including those of the liver, esophagus and gallbladder. "It is a combination of the effects of hormones, mechanical and chemical inflammation," Thun says.

Here's the catch, though. There's little evidence that losing excess weight will improve your odds of avoiding cancer. The key, says Thun, is to avoid weight gain in the first place.

Recommendation: Maintain a healthy body weight, beginning in childhood.

Physical inactivity

"The sedentary lifestyle is a big contributor to cancer, we now think," says Higginbotham - and not just because it leads to weight gain. Research is suggesting there's something risky about inactivity itself.

The strongest evidence involves colon cancer. One review found that just getting exercise reduced colon cancer risk by 50 percent, regardless of the intensity of the workout. Even moderate exercise, such as brisk walking for three to four hours per week, was shown in one study to lower colon cancer risk. Thun believes exercise may speed up your digestive processes, so that food moves faster through your system. The quicker the transit times of food through the colon, the lower the risk of cancer.

With breast cancer, a 2003 study in the Journal of the American Medical Association reported that as little as 30 minutes a day of walking could mean a 20 percent reduction in risk. The effects were strongest among women in the normal weight range, where the study showed a 37 percent risk reduction. The National Cancer Institute has linked lack of physical activity to other cancers as well, including cancers of the esophagus, kidneys and uterus.

Recommendation: Exercise regularly. If possible, aim for at least 30 minutes every day.

Drinking past moderation

"Heavy drinking increases the risk of about five cancers in your upper airway and digestive tract," says Thun. The organs affected are the mouth, esophagus, pharynx, larynx and liver.

Even moderate amounts of alcohol have recently been linked to an increased risk for breast cancer in women who are in menopause. The mechanisms for this observed association are still unclear: Researchers are looking into a possible effect of estrogen levels and into genetic differences among individuals in an enzyme that breaks down alcohol.

Recommendation: No more than two drinks a day for men and one for women.

Smoking

This should be old news. Smoking is by far the most researched and proven cause of cancer, a true slam dunk, going back to the 1964 Surgeon General's report. According to the National Cancer Institute, more than 180,000 Americans die every year from cancer related to tobacco: smoking, chewing or breathing in somebody else's smoke. Thun notes that smoking has been linked to 15 types of cancer, including mouth, throat, esophagus and lung, liver, stomach, colon, kidney, bladder and even cervix. It is no surprise, he says, because cigarette smoke has "40 different known carcinogens." If you're a smoker, the younger you quit, the better your odds.

Recommendation: Obvious.

Playing it safe

A study in the September issue of Cancer Epidemiology, Biomarkers & Prevention showed that eating a variety of fruits and vegetables could decrease the risk of a certain type of lung cancer, especially among smokers.

What about reducing your consumption of specific foods or your use of certain products, as a hedge against cancer? Here's a list of choices you can make to play it safe, though evidence for some is significantly weaker than the evidence in the studies mentioned above.

Sun Exposure

Cancer link: Skin, eye.

Sun exposure has been a well-known cause of skin cancers, from the less serious basal cell carcinoma to the deadlier melanoma. In recent months, various organizations and experts have turned the heat up on tanning beds and tanning lamps, calling for restrictions on their use. In the largest study of it kind, published in the May issue of Cancer Epidemiology, Biomarkers & Prevention, authors noted that tanning beds increased the risk of melanoma between twofold and fourfold, depending on the device.

Sugary drinks

Cancer link: Pancreas.

A recent study in the journal Cancer Prevention showed that people who drank two or more soft drinks a week had a higher risk of pancreatic cancer, one of the deadliest forms of the disease. At this point, there are not enough studies to prove an association or a cause, and this topic remains, according to Higginbotham, a "very contentious and active area of research."

Talcum

Cancer link: Ovaries, uterus.

Talcum - used in body, facial and baby powders - has been linked to tumors of the ovaries. A recent study in Cancer Epidemiology, Biomarkers & Prevention suggests its use in the genital area may increase the risk of cancer in the lining of the uterus. Overall, however, studies have been inconsistent.

Radon

Cancer link: Lung.

Radon is an odorless and colorless radioactive gas, often found in soil, that can seep into buildings through cracks in foundation walls and floors. If the buildings are insufficiently ventilated, levels of the gas can accumulate. The Environmental Protection Agency says exposure to radon in the home is responsible for an estimated 20,000 lung cancer deaths each year in the United States. There are home tests for radon; for confirmed readings of 4 picocuries per liter or higher, the EPA recommends taking corrective action.

Pesticides

Cancer link: Various.

Studies of individuals exposed to pesticides at work, such as farmers, certain factory workers and crop-dusters, have shown that high levels were associated with cancers of the blood and lymph system, as well as cancers of the lip, stomach, lung, brain, prostate and skin.

Cellphones

Cancer link: Face, neck, brain.

A long-awaited study was published in May by the World Health Organization's International Agency for Research on Cancer. The report looked at the association of cellphone use and two types of brain cancers, and found it to be inconclusive. It did, however, suggest that using cellphones for more than 30 minutes every day increased the risk of glioma, a benign type of brain tumor. Call duration seemed to be riskier than the number of calls made each day, according to the authors.

Red and processed meat.

Cancer link: Colon.

Several studies have linked meat consumption to cancer of the colon. The risks, Thun says, are not "in the same league" as the risk from smoking or being obese, but they are worth considering, especially since meat is a major component of the U.S. diet.

Let's be clear. These are guidelines, not a promise you'll never get cancer if you follow this advice. Genetics count. So do things in the environment over which you have no control.

Cancer also afflicts nonsmoking slim people who eat well and work out often. But many of these lifestyle changes come with so many other benefits, beyond helping prevent cancer - weight loss to feel good, sunscreen for less-wrinkled skin - that it makes sense to adopt them anyway.

- Ranit Mishori

health-science@washpost.com

Mishori is a family physician and faculty member in the Department of Family Medicine at Georgetown University School of Medicine.

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