Obesity and Cancer Risk (Fact Sheet)

Obesity and Cancer Risk (Fact Sheet)
Obesity and Cancer Risk (Fact Sheet)

Key Points

  • During the past several decades, the percentage of overweight and obese adults and children has increased markedly.
  • Obesity is associated with increased risks of cancers of the esophagus, breast (postmenopausal), endometrium (the lining of the uterus), colon and rectum, kidney, pancreas, thyroid, gallbladder, and possibly other cancer types.
  • Obese people are also at higher risk of coronary heart disease, stroke, high blood pressure, diabetes, and a number of other chronic diseases.

What is obesity?

Obesity is a condition in which a person has an abnormally high and unhealthy proportion of body fat.

To measure obesity, researchers commonly use a scale known as the body mass index (BMI). BMI is calculated by dividing a person's weight (in kilograms) by their height (in meters) squared. BMI provides a more accurate measure of obesity or being overweight than weight alone.

Guidelines established by the National Institutes of Health (NIH) place adults age 20 and older into the following categories based on their BMI:

BMI Categories
Below 18.5
18.5 to 24.9
25.0 to 29.9
30.0 and above

The Oncology Nurse Advisor website provides a BMI calculator.

For children and adolescents (less than 20 years of age), overweight and obesity are based on the Centers for Disease Control and Prevention's (CDC) BMI-for-age growth charts:

BMI Categories
BMI-for-age at or above sex-specific 85th percentile, but less than 95th percentile
BMI-for-age at or above sex-specific 95th percentile

Compared with people of normal weight, those who are overweight or obese are at greater risk for many diseases, including diabetes, high blood pressure, cardiovascular diseases, stroke, and certain cancers.

How common is overweight or obesity?

Results from the 2007-2008 National Health and Nutrition Examination Survey (NHANES) show that 68 percent of U.S. adults age 20 years and older are overweight or obese. In 1988-1994, by contrast, only 56 percent of adults age 20 and older were overweight or obese.

In addition, the percentage of children who are overweight or obese has also increased. Among children and teens ages 2 to 19, 17 percent are estimated to be obese, based on the 2007–2008 survey. In 1988–1994, that figure was only 10 percent. 

What is known about the relationship between obesity and cancer?

Obesity is associated with increased risks of the following cancer types, and possibly others as well:

  • Esophagus
  • Pancreas
  • Colon and rectum
  • Breast (after menopause)
  • Endometrium (lining of the uterus)
  • Kidney
  • Thyroid
  • Gallbladder

One study, using NCI Surveillance, Epidemiology, and End Results (SEER) data, estimated that in 2007 in the United States, about 34,000 new cases of cancer in men (4 percent) and 50,500 in women (7 percent) were due to obesity. The percentage of cases attributed to obesity varied widely for different cancer types but was as high as 40 percent for some cancers, particularly endometrial cancer and esophageal adenocarcinoma.

A projection of the future health and economic burden of obesity in 2030 estimated that continuation of existing trends in obesity will lead to about 500,000 additional cases of cancer in the United States by 2030. This analysis also found that if every adult reduced their BMI by 1 percent, which would be equivalent to a weight loss of roughly 1 kg (or 2.2 lbs) for an adult of average weight, this would prevent the increase in the number of cancer cases and actually result in the avoidance of about 100,000 new cases of cancer.

Several possible mechanisms have been suggested to explain the association of obesity with increased risk of certain cancers:

• Fat tissue produces excess amounts of estrogen, high levels of which have been associated with the risk of breast, endometrial, and some other cancers.

• Obese people often have increased levels of insulin and insulin-like growth factor-1 (IGF-1) in their blood (a condition known as hyperinsulinemia or insulin resistance), which may promote the development of certain tumors.

• Fat cells produce hormones, called adipokines, that may stimulate or inhibit cell growth. For example, leptin, which is more abundant in obese people, seems to promote cell proliferation, whereas adiponectin, which is less abundant in obese people, may have antiproliferative effects.

• Fat cells may also have direct and indirect effects on other tumor growth regulators, including mammalian target of rapamycin (mTOR) and AMP-activated protein kinase.

• Obese people often have chronic low-level, or “subacute,” inflammation, which has been associated with increased cancer risk.

Other possible mechanisms include altered immune responses, effects on the nuclear factor kappa beta system, and oxidative stress. 

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