Cancer and Obesity

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

What Evidence is There of Obesity Leading to Cancer?

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%) and 50,500 in women (7%) were due to obesity.

The percentage of cases attributed to obesity varied widely for different cancer types but was as high as 40% for some cancers, particularly endometrial cancer and esophageal adenocarcinoma.

Impact of Obesity on Society

A projection of the future health and economic burden of obesity in 2030 estimated that the continuation of existing trends in obesity will lead to about 500,000 additional cases of cancer in the United States by 2030. Equivalent figures are echoed in Australian studies.

Reducing the Impact of Obesity

This analysis also found that if every adult reduced their BMI by 1% or the equivalent of roughly 1kg for an average adult’s weight would prevent the increase in the number of cancer cases and actually result in the avoidance of about 100,000 new cases of cancer in the US.

Why Does Obesity Cause 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 in their blood (a condition known as hyperinsulinemia or insulin resistance), which may promote the development of certain tumours,
  
• 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 tumour growth regulators, including the 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.
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Other possible mechanisms include altered immune responses, effects on the nuclear factor kappa beta system, and oxidative stress.



Source: http://www.cancer.gov/cancertopics/factsheet/Risk/obesity