Overweight, Obesity Linked to Cancers

Pancreatic Cancer Slideshow

Study Shows High Body Mass Index Ups Risk of Common and Rare Cancers

By Salynn Boyles
WebMD Health News

Reviewed By Louise Chang, MD

Feb. 14, 2008 -- If you're overweight or obese you have an increased risk for developing many common and not-so-common cancers, a research analysis shows.

Researchers combined data from more than 200 sets of data -- including more than 282,000 people -- that considered the impact of weight on 15 cancer sites.

Increased weight was most strongly linked to an increased risk for cancer of the esophagus in men and women and for endometrial and gallbladder cancers in women.

A modest association was found between excess weight and the risk for more common malignancies such as postmenopausal breast cancer in women, colon cancer in men, and blood cancer in both sexes.

But carrying extra weight was not associated with an increase in risk for prostate cancer in men, premenopausal breast cancer and ovarian cancer in women, and lung cancer in men and women.

The analysis appears in the Feb. 16 issue of The Lancet.

"We were surprised to find associations to both common and less common cancers," researcher Andrew G. Renehan, PhD, tells WebMD. "We also saw very clear differences between [obesity-related] risk at different sites between the sexes."

BMI and Cancer Risk

Renehan and colleagues from the University of Manchester in England used body mass index (BMI) measures from the studies to assess risk.

BMI is a numerical measure of fatness based on a person's weight relative to height. A BMI of 18.5 to below 25 is considered normal weight, while 25 to just under 30 is considered overweight, but not obese. Someone is considered obese if they have a BMI of 30 or above.

To put the numbers in perspective, someone who is 5-feet 7-inches tall would have a BMI of 25, 30, or 35, respectively, if they weighed 160, 190, or 225 pounds.

In men and women, each 5-point increase in BMI was associated with a roughly 50% increase in relative risk for esophageal adenocarcinoma, which is still relatively uncommon but growing in the U.S.

Other highlights from the analysis include:

• Among women, each 5-point increase in BMI was associated with a roughly 60% increase in risk for endometrial (uterine) cancer. About 39,000 new cases of the cancer were estimated in the U.S. last year, with 7,400 estimated deaths from the disease. 
• The link between overweight and obesity and colon cancer was stronger in men than in women; each 5-point increase in BMI was associated with a 24% increase in relative risk among men and a 9% increase in women. 
• Excess weight was a much stronger risk factor for gallbladder cancer in women than in men, with each 5-point increase in BMI associated with a 59% increase in the relative risk for the cancer in women and no statistically significant increase in men. Gallbladder cancer is rare, with only about an estimated 9,000 new cases diagnosed last year in the U.S. 
• Each 5-point increase in BMI was associated with a 12% increase in the risk of breast cancer after menopause in women, but no increase in risk prior to menopause. 
• Increased BMI was also associated with a modest increased risk for blood cancers like leukemia, multiple myeloma, and non-Hodgkin's lymphoma in both men and women.

Estimating Future Risk

Being able to quantify cancer risk in relation to body weight should help public health officials estimate the impact of both the aging of the population and the obesity epidemic on cancer rates over the next decade and beyond, Renehan says.

Nutritional epidemiologist Susanna Larsson, PhD, of Stockholm's Karolinska Institutet tells WebMD that the analysis makes it clear that more needs to be done at the community level to help people maintain healthy body weights.

"We have not seen the initiatives that will be needed to address this problem," she says.

American Cancer Society epidemiologist Michael Thun, MD, MS, agrees.

"If people could lose weight easily they would," he tells WebMD. "But the fact is, there are many, many things in our social and physical environment that make it easy to gain weight. Food is everywhere, and physical activity is no longer built into our daily lives. For most people it is voluntary."

Although awareness is growing, Thun says most people still don't know that being overweight or obese makes them more likely to get cancer.

"They know that obesity is linked to heart disease and diabetes," he says. "But the average person on the street would still be surprised that obesity is related to cancer risk."

SOURCES: Renehan, A.G. The Lancet, Feb. 16, 2008; vol 371: pp 569-578. Andrew G. Renehan, PhD, department of surgery, School of Cancer Studies, University of Manchester, England. Susanna C. Larsson, PhD, division of nutritional epidemiology, National Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. Michael J. Thun, MD, MS, vice president of epidemiology and surveillance research, American Cancer Society, Atlanta. National Cancer Institute web site. American Cancer Society web site.

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