Obesity And Cancer: A Deadly Link

by Jennifer Wider, M.D.

(Washington DC, 5/1/03):  The risk of dying from cancer increases significantly for both men and women who are obese, according to a new study published April 24, 2003 in The New England Journal of Medicine. This increased risk is shown to affect women more often than men. Being overweight or obese, categories defined by measuring body mass index (BMI) accounts for roughly 14 percent of cancer deaths in men and 20 percent of deaths in women, according to the results of the study.

In this prospective study, researchers from the American Cancer Society examined the relationship between BMI and death from cancer in more than 900,000 adults. They found that increased body weight raises the risk of death from all cancers combined and from cancers at multiple specific sites. In addition, among patients in the heaviest weight category, with a BMI greater than or equal to 40, the risk of cancer death was 52 percent higher in men and 62 percent higher in women when compared with normal weight adults. BMI is calculated by dividing weight (kilograms) by height (meters) squared.

Women are affected more often than men for several reasons. Many studies have established a strong association between breast cancer risk and increased body weight and only a modest association between prostate cancer and obesity. "Obese women double their risk of breast cancer," according to Dr. Carmen Rodriguez, MD, MPH Senior Epidemiologist at the American Cancer Society and one of the authors of the study. Therefore, increased body weight plays a more significant role among women compared to men suffering from the most common forms of cancer. In addition, Dr. Rodriguez explains: "the percentage of obese women is higher than men, 33% versus 28%."

The incidence of obesity in the United States has increased significantly over the last two decades. According to the Centers for Disease Control and Prevention, obesity is defined as a BMI greater than or equal to 30. To be classified as overweight, the BMI is between 25 and 29.9. Recent data from the National Center for Health Statistics in Hyattsville, Maryland, shows that roughly 31 percent of the adult population aged 20 years or older meet the criteria for obesity. And the numbers continue to rise.

While the reasons underlying the association between cancer death and obesity are not fully understood, female hormones are thought to play a role. "Obesity increases the risk of breast cancer only among post-menopausal women," explains Dr. Rodriguez. Because many post-menopausal breast cancers are stimulated by estrogen and fat increases circulating hormones in the body, the risk of cancer increases for obese women.

Obesity has been linked to many serious health conditions, including cardiovascular disease, diabetes, stroke, and high blood pressure. According to Dr. Rodriguez, there aren't many studies showing that weight control programs lower the risk of cancer death: "We can speculate that if you lower your weight, you will lower your risk as well. But it is not easy to do an observational study with enough people who have been obese and lower and maintain their weight." She recommends maintaining a healthy weight as well as good nutrition and exercise habits throughout life.

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The Society for Women's Health Research is the nation's only not-for-profit organization whose sole mission is to improve the health of women through research. Founded in 1990, the Society brought to national attention the need for the appropriate inclusion of women in major medical research studies and the resulting need for more information about conditions affecting women. The Society advocates increased funding for research on women's health, encourages the study of sex differences that may affect the prevention, diagnosis and treatment of disease, and promotes the inclusion of women in medical research studies. Dr. Donnica Moore has been a member of the Society since 1990 and is a past member of its Board of Directors.

Created: 5/1/2003  -  Jennifer Wider, M.D.
Reviewed: 5/1/2003  -  Donnica Moore, M.D.