Online Extra: What's Fueling the Cancer Epidemic

Beyond an aging population, smoking and poor diet are the disease's leading -- and most avoidable -- causes

The causes of cancer are myriad and complex, but it has one overriding driver -- old age. The longer we live, the more opportunities genetic mistakes have to build up in our bodies, until one day a cell mutates and becomes cancerous.

So if it seems as though the number of people you know with cancer is on a dramatic upswing, you're probably a member of the baby-boom generation. Cancer is the leading cause of death among women age 40 to 79 and among men age 60 to 79. By comparison, cancer is only the fifth-leading cause of death for men 20 to 39. Consequently, the National Cancer Institutes believes that as the population both ages and expands, it's inevitable that within 10 to 15 years cancer will overtake heart disease to become the leading cause of death in the U.S.

STOP SMOKING.

  Aging aside, lifestyle will go a long way toward determining whether you'll succumb to this dread disease. Only some 5% of cancers are inherited, and an additional 5% to 10% might be linked to environmental and workplace pollutants, according to various studies. Excessive sunburn causes approximately 90% of skin cancers.

The biggest culprit, however, is a glaring -- and avoidable -- pollutant. "You want to avoid cancer? Stop smoking," asserts Robert A. Weinberg, a leading cancer researcher at the Whitehead Institute for Biomedical Research in Cambridge, Mass.

The American Cancer Society attributes more than 30% of all cancer deaths in the U.S. to tobacco smoking, and 90% of all lung cancer cases can be directly linked to smoking. Given that lung cancer kills more people each year than colon, breast, and prostate cancer combined, it's easy to understand why cigarettes are sometimes referred to as coffin nails.

FAT CHANCE.

  While the perils of cigarettes may be well known, many people may not realize that their diets can be almost as dangerous. The ACS estimates that almost 30% of cancer cases can be traced to a diet of excessive fat, low fiber, and too few fruits and vegetables. In colon cancer, the No. 2 killer cancer, the link to diet could be as high as 90%, says Weinberg. It's well established that colon cancer is significantly less common in Japan and Finland, where low-fat diets are more the norm, than in the rest of the Western world.

Obesity in particular is a high risk factor for cancer. Fat cells produce some 15 to 20 chemicals that can cause tumor growth, and the heavier a person is, the bigger the fat cells. And they chrun out more toxic stuff. "Thirty to forty percent of cancers could be avoided with diet, physical activity, and weight loss," says Dr. George A. Bray, professor of medicine at Louisiana State University Medical Center.

Unfortunately, the damage caused by decades of smoking and bad diet cannot be undone in a few years. Waiting until you are 50 to change your ways may do little good. "By the time people start thinking about cancer they've already done the damage," says Dr. Lee Ellis, professor of cancer biology and surgical oncology at M.D. Anderson Cancer Center in Houston. "It takes 15 to 20 years of exposure to cause that kind of damage. You can't undo that in a few years."

A good message to tell your kids.

By Catherine Arnst in New York, with John Carey in Washington

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