Excess Weight Means Extra Cancer Risk

American Institute for Cancer Research
Sunday, 1 February 2004

Convincing research results link obesity with higher risk of cancer. During National Cancer Prevention Month, researchers are warning Americans that they can reduce the odds of getting cancer by avoiding excessive weight gain.

"We know that obesity is linked to some of the most common cancers, and we suspect that links to others will soon be demonstrated. Here is another pressing reason for all of us to think about maintaining a healthy body weight," said Melanie Polk, R.D., Director of Nutrition Education at the American Institute for Cancer Research (AICR).

A 2002 report issued by the World Health Organization's International Agency for Research on Cancer estimates that one-fifth to one-third of all breast, colon, endometrial, kidney and esophageal cancers can be related to overweight and obesity.

In a recent population study published in the New England Journal of Medicine (April 24, 2003), researchers conclude that overweight and obesity account for up to 14 percent of all cancer deaths in American men over 50 and 20 percent of all cancer deaths in American women over 50. The researchers estimated that more than 90,000 deaths from cancer per year could be avoided if all adults maintained a normal body weight throughout life.

Explaining the Link

Scientists continue to probe just how excess body weight increases cancer risk. They are focusing on metabolic and hormonal changes produced by overweight and inactivity that may promote the cancer process.

Fat cells are known to secrete hormones and hormone-like substances into the blood stream to help cells grow properly. Many scientists believe that in people with excess body fat, greater amounts of hormones are produced causing cells to grow and divide rapidly. Under these conditions, the chances increase that cell division will go wrong, leading to cancer.

For instance, excess body fat has been linked to postmenopausal breast cancer because of its effect on estrogen levels. Although the ovaries stop producing estrogen after menopause, fat cells continue to pump the hormone into the blood stream. Scientists believe that this extended lifetime exposure to estrogen increases breast cancer risk after menopause.

A similar mechanism may be operative in regard to prostate cancer. In two brand new studies reported in the Journal of Clinical Oncology (February 1, 2004 on-line), a higher risk of recurrence and more aggressive tumors were found in obese men who had had surgery for prostate cancer than in men with lower body weights. One explanation offered is that obesity-induced changes in hormone level may promote the progression of a tumor to a more aggressive type of prostate cancer.

Since body fat produces a range of hormones, some scientists predict that research will connect excessive fat to the development of all "hormonal" cancersóbreast, prostate, ovary, endometrial and testes.

Steps You Can Take

"The risk of cancer is another incentive for people to consider their weight and take steps to hold it at a healthy level or reduce it if necessary," Polk said.

AICR recommends replacing fatty foods with vegetables and fruits and increasing physical activity as the first steps toward weight loss. People concerned about shedding pounds should also consider gradually reducing the size of the portions they eat, Polk advises.

"If restricting caloric intake and increasing physical activity do not lead to gradual weight loss, people should consult a physician or a registered dietitian for an individual weight management plan," Polk said.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org

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