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New Estimate: Excess Body Fat Alone Causes Over 100,000 Cancers in U.S. Each Year

By Shelly Bender

Researchers Present Data Linking Obesity/Overweight to Higher Cancer Risk and Poorer Cancer Survival

Well, if what you already know about obesity and the negative effects it can have on your body, mind and spirit aren’t enough to make you want to lose the excess weight, how about this startling fact: According to a recent American Institute for Cancer Research (AICR)/World Cancer Research Fund International (WCRF International) report, approximately 100,500 cancers occurring in the U.S. every year can be attributed to excess body fat, according to estimates released this year. The figure underscores the central role that overweight and obesity are now understood to play both in the development of cancer and in cancer survivorship, said researchers.

According to AICR, the estimated number of cancers that are linked to excess body fat include:

• 49% of endometrial cancers1 = 20,700 cases/year2
• 35% of esophageal cancers = 5,800 cases/year
• 28% of pancreatic cancers =11,900 cases/year
• 24% of kidney cancers =13,900 cases/year
• 21% of gallbladder cancers = 2,000 cases/year
• 17% of breast cancers* = 33,000 cases/year
• 9% of colorectal cancers =13,200 cases/year

Total: 100,500 cases/year

¹ Percentages from AICR/WCRF’s Policy and Action for Cancer Prevention, 2009
² Calculated from total estimated incidence, Cancer Facts and Figures 2009, ACS
* Post-menopausal

Laurence Kolonel, MD, PhD, Deputy Director of the Cancer Research Center of Hawaii and AICR/WCRF expert panel member, presented the new preventability estimates and reviewed the evidence linking obesity to cancer risk. “We now know that carrying excess body fat plays a central role in many of the most common cancers,” he said. “And it’s clearer than ever that obesity’s impact is felt before, during and after cancer—it increases risk, makes treatment more difficult and shortens survival.”

Dr. Kolonel also highlighted the emerging evidence that is revealing the nature of the link between excess body fat and cancer. Some of the strongest evidence, he noted, suggests that excess body fat increases the body’s level of sex steroids and other hormones that are linked to cancer growth. For example, fat tissue produces estrogen; studies have shown that estrogen promotes cell proliferation in breast tumors that contain receptors for the hormone, the so-called ER positive tumors. Recent finding also suggest that excess body fat lowers immune function and increases oxidative stress, which can lead to DNA damage.

Emerging Evidence Implicates Obesity and Overweight in Poor Cancer Survivorship

Melinda Irwin, Phd, MPH, Associate Professor of Epidemiology at Yale University, presented evidence that overweight and obesity continue to play a negative role after cancer has been successfully treated. Dr. Irwin stressed, however, that there are two ways of looking at data linking higher Body Mass Index (BMI) to poorer survival, and she prefers the one that encourages survivors to get active.

“It’s true that higher BMI is associated with poorer outcomes. Now we need to ask why this is the case,” she said. “An increasing number of studies suggest that regular physical activity improves cancer survival, even among survivors who are overweight or obese. That’s really the take-home message here.”

Dr. Irwin reviewed data showing that although obesity increases risk of death among cancer survivors, some factors that influence obesity, such as physical activity, have also been shown to have an impact on survival that is independent of BMI. A growing number of publications, for example, have reported that increasing physical activity after diagnosis, especially among those who were inactive before they were diagnosed, is associated with an improvement in survival.

“We now know that carrying excess body fat plays a central role in many of the most common cancers,” he said. “And it’s clearer than ever that obesity’s impact is felt before, during and after cancer—it increases risk, makes treatment more difficult and shortens survival.”

One reason for the association between physical activity and better outcome said Irwin, may have to do with the fact that regular physical activity helps to regulate hormone levels. Studies have shown that women with high insulin levels at diagnosis have a 2 to 3-fold increased risk of death than is seen among women with low insulin levels. (High insulin levels are associated with inactivity and overweight).

Dr. Irwin presented recent findings from her own Yale Exercise and Survivorship (YES) Study intervention trial, which showed that within 6 months, regular exercise decreased insulin levels by about 8% among 933 breast cancer survivors. She concluded her remarks by encouraging clinicians to recommend exercise to their survivor patients, and praising the growing number of exercise programs available to cancer survivors.

Only 51 Percent of Americans Now Realize That Obesity is a Cause of Cancer

Americans dread cancer, but remain confused about its causes. The latest results from the biennial AICR Cancer Risk Awareness Survey, which measures cancer risk awareness, show that only about half of Americans realize that carrying excess body fat places them at significantly higher risk for several cancers. The survey also reveals that although cancer ranks as the nation’s #1 health concern, only a small percentage of Americans realize that many cancers are highly preventable.

Although awareness of the obesity cancer-link has edged over 50 percent for the first time since the survey began in 2001, experts at the AICR, who commissioned the survey, expressed concern today that the latest results show body fatness—a major cause of cancer—still lagging far behind other known risk factors.

“In light of the fact that excess body fat causes over 100,000 cancer cases each year in this country—cases that could be prevented by staying lean—public awareness of the link remains alarmingly low,” said AICR Nutrition Communications Manager, Alice Bender, MS, RD, who presented the results of the survey at a press conference coinciding with AICR’s Annual Research Conference on Food Nutrition, Physical Activity and Cancer in Washington, DC. “It’s a message that desperately needs to be heard.”

“In light of the fact that excess body fat causes over 100,000 cancer cases each year in this country—cases that could be prevented by staying lean—public awareness of the link remains alarmingly low,”

Awareness that tobacco use and excessive exposure to sunlight are cancer risks has remained high throughout the survey’s history (tobacco now stands at 94 percent awareness, sun exposure at 87 percent). But the percentage of Americans who can identify other factors that have also been convincingly linked to increased cancer risk is much lower at 51 percent. According to the AICR, most cancers are preventable: About one-third of the most common cancers could be prevented through diet, physical activity and weight management.

Bender also pointed to the conclusions of AICR’s Policy Report, released earlier this year. “While it’s very important for individuals to make healthy changes, it is also critical that all sectors of society—government, schools, food industry, workplaces, health professionals—work toward policies and environments that support healthy weight,” she said.

For more information see American Institute for Cancer Research (AICR)