Cancer Prevention: What Works?

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Soy, fish oil, and alcohol are still debated, but some things are certain: Stop smoking, lose weight, and exercise.

By Richard Trubo
WebMD Feature

Reviewed By Michael Smith

Cancer has surpassed heart disease to become the No. 1 cause of death in the U.S. in people under age 85. No wonder more people than ever are turning their attention to cancer prevention strategies that might protect them from becoming a statistic. But the question lingers, which approaches really work? And which may be little more than hype or wishful thinking?

If you're concerned about cancer prevention, one of your challenges is to sort through the research reported in the media and make sense of findings from highly publicized studies that are often contradictory.

"One week, there might be a study that suggests that high coffee intake causes cancer, and the next week, we'll hear about another study concluding that coffee consumption has no relationship to cancer," says Scott Litin, MD, editor-in-chief of the Mayo Clinic Family Health Book and professor of medicine at Mayo Medical School. "News organizations want to report the latest information, but this doesn't always mean it's the most reliable or the best done study. There is a lot of confusion out there, and in many areas, the medical profession doesn't yet know what's going to pan out and what won't."

In some areas of cancer prevention, carefully conducted and controlled studies just haven't been performed yet. "Many claims have been made, but until the research is done, we just don't know which reduce the risk of cancer, which have no effect, and which are harmful," says Cynthia Stein, MD, MPH, of the Harvard Center for Cancer Prevention at Harvard Medical School.

What's Fact? What's Not?

Take high-fat diets. "Ten years ago, cutting down on fat in the diet to lower cancer risk was one of our major recommendations," says Melanie Polk, MMSc, RD, director of nutrition education at the American Institute for Cancer Research in Washington, D.C. "At the time, the evidence indicated that excessive fat in the diet could promote the cancer process."

But, says Polk, the relative importance of fat restriction in cancer prevention is changing as more studies are done. "The research now supports a mostly plant-based diet emphasizing fruits and vegetables as protective of cancer," she says. "The evidence in this area far outweighs the research into fat. So while we still believe that eating a lower-fat diet is one approach to lowering your cancer risk, even more important is to eat a mostly plant-based diet. At least 20% of cancer cases could be avoided by eating at least five servings of fruits and vegetables a day."

In particular, says Stein, there is evidence that by increasing your consumption of fruits and vegetables, you may be able to lower your risk of cancers of the bladder, esophagus, pancreas, lung, and oral cavity.

Therese Bevers, MD, medical director of clinical cancer prevention at the University of Texas M.D. Anderson Cancer Center in Houston, concurs that a healthy diet is important and may reduce the risk of developing cancer. But, she adds, doctors are awaiting more definitive data on the optimal diet for cancer prevention. "Some studies have shown that reducing your dietary fats can lower your risk of breast cancer, but others have shown no such benefit," she says.

Weighing the Evidence

There is plenty of hype in many areas of cancer prevention, even when the scientific evidence isn't persuasive. For example:

• The joy of soy? Women in Asia have lower rates of breast cancer than their counterparts in the Western world -- and they also have a much higher intake of soy. That kind of news has driven some women to take soy to extremes.
  
  "There are people eating soy milk at breakfast, soy burgers at lunch, and tofu at dinner, and snacking on soy nuts throughout the day because they think that soy is going to save their lives," says Polk. "But we just don't have long-term studies to support the intake of these huge amounts of soy. If you enjoy partaking in soy, go ahead, but when it comes to eating it in very large amounts, we really don't know enough to say if it is definitely helpful or harmful."
  
  
• Looking to the sea. Fish has been touted as a weapon in cancer prevention, but many experts aren't yet convinced that the oils in fish -- called omega-3 fatty acids -- have really turned the tide in human studies. Nevertheless, some animal research suggests that omega-3s may reduce cancer risk. If you want to give fish a try, concentrate on the fatty fish such as salmon, herring, mackerel, and sardines.
  
  
• Drinking to Your Health? Although you have probably heard that a daily glass or two of wine or other alcoholic beverages may improve your heart health, don't count on that bottle of Bordeaux for cancer prevention. In fact, the opposite may be true.
  
  "As little as one drink per day (one beer, one glass of wine, or one shot of liquor) increases the risk of breast and colon cancer," says Stein. "It also increases the risk of cancers of the mouth, larynx, esophagus, and liver."
  
  So if you do enjoy an alcoholic drink now and then, don't overdo it. "We usually advise limiting your consumption to one alcoholic beverage or less per day on average," says Bevers.

Controversial and Unproven

Although you might read about various links between cancer and certain lifestyle choices, many of these claims haven't impressed the serious scientists. Internet emails, for example, have proclaimed that chemicals in underarm antiperspirants are absorbed through the skin and interfere with normal circulation, causing toxins to build up and trigger breast cancer. But according to the American Cancer Society (ACS), there is "no experimental or epidemiological evidence to support this rumor."

One popular urban legend has implicated underwire bras as a cause of breast cancer, claiming that they obstruct lymph circulation, although the ACS insists that there is no credible research that supports this claim. There is probably no need to give up coffee, either -- at least not now. Caffeine may increase symptoms of fibrocystic breast lumps, but there is no proof that this benign breast disease increases the likelihood of breast cancer.

What Makes Sense?

So what should you do for cancer prevention? "At least 50% of cancers in the U.S. could be prevented just based on what we already know about risk factors," says Stein. Here are some recommendations to take seriously:

• Stop smoking or using tobacco products. In 2002, tobacco use caused more than 430,000 deaths from cancer and other serious diseases. Tobacco is a major cause of preventable disease and premature death. It increases the risk for cancer of the lung, esophagus, pancreas, kidney, bladder, and uterine cervix. For cancer prevention, throw out your cigarettes and avoid secondhand or environmental tobacco smoke, too.
• Protect your skin in the sun. The majority of skin cancers are caused by excess ultraviolet radiation exposure, most of which comes from the sun. Wear SPF 15 (or higher) sunscreen and a wide-brimmed hat to guard against skin cancer. Avoid direct sunlight during the hours when the sun's ultraviolet rays are the strongest (between 10 a.m. and 4 p.m.). The American cancer Society also recommends avoiding tanning beds and sun lamps.
• Lose any excess pounds. About 64% of men and women in the U.S. were overweight or obese in 1999, based on data from the surgeon general, and over 25% of the U.S. population is obese. According to the ACS, about a third of all cancer deaths from 2002 were expected to be related to nutrition, physical inactivity, obesity, and other lifestyle factors and could have been prevented. An ACS study in the April issue of The New England Journal of Medicine suggests that about 14% of all cancer deaths in men and 20% of those in women are associated with excess body weight.
  
  "If there were one perfect way to lose weight, you wouldn't go into the bookstore and find a hundred different diet books," says Litin. "It boils down to this: Healthy eating, consuming less calories than you burn up, and doing more exercise."
  
  
• Fiber up. Although doctors continue to debate the cancer prevention effects of a diet rich in fiber (emphasizing whole-grain products, cereals, vegetables, and fruits), two major studies published in the British medical journal The Lancet in May found that the risk of colorectal cancer was reduced with high intakes of dietary fiber. In one of those studies, conducted in 10 European countries, the individuals who consumed the most dietary fiber (averaging 35 grams a day) experienced a 40% lower risk of colon cancer than subjects eating the least fiber (averaging 15 grams a day).
• Get active. Exercise may help regulate hormones and "growth factors" that have been linked to cancer. According to Stein, all adults should accumulate at least 30 minutes of moderate-intensity activity on most days of the week, including walking, bicycling, gardening, dancing, and cleaning. This activity, she says, "does not need to be done all at once -- 10 minutes here and there add up."
• Consider "chemoprevention." If you're at high risk for breast cancer (because of a strong family history, for example), your doctor may recommend taking a prescription drug called tamoxifen to reduce your chances of developing the disease. However, in a report in July 2002, the U.S. Preventive Services Task Force advised that the drug not be given to women with a low or average breast cancer risk.
• Get tested. Annual screenings are advisable for all adults. Early detection, says Bevers, offers the best chance of successful treatment.

Originally published May 23, 2003.

Medically updated Jan. 24, 2005.

SOURCES: Therese Bevers, MD, University of Texas M.D. Anderson Cancer Center, Houston. Scott Litin, MD, Mayo Medical School, Rochester, Minn. Melanie Polk, MMSc, RD, American Institute for Cancer Prevention, Washington, D.C. Cynthia Stein, MD, MPH, Harvard Center for Cancer Prevention, Harvard Medical School, Boston.

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