Overweight, Obesity and Cancer

The prevalence of obesity is rapidly increasing globally. Epidemiological studies have associated obesity with a range of cancer types, although the mechanisms by which obesity induces or promotes tumorigenesis vary by cancer site. These include insulin resistance and resultant chronic hyperinsulinaemia, increased bioavailability of steroid hormones and localized inflammation.

Gaining a better understanding of the relationship between obesity and cancer can provide new insight into mechanisms of cancer pathogenesis.

Introduction

The prevalence of overweight and obesity in most developed countries (and in urban areas of many less developed countries) has been increasing markedly over the past two decades. By the year 2000, nearly two-thirds of adults in the United States were overweight or obese, and there were 300 million obese adults worldwide. The incidence of type-II diabetes during this same time period has mirrored, and is presumed to be a direct result of, the obesity epidemic. Although obesity has long been recognized as an important cause of diabetes and cardiovascular diseases, the relationship between obesity and different types of cancer has received less attention than its cardiovascular effects.

Results from epidemiological studies that largely began in the 1970s indicate that adiposity contributes to the increased incidence and/or death from cancers of the colon, breast (in postmenopausal women), endometrium, kidney (renal cell), oesophagus (adenocarcinoma), gastric cardia, pancreas, gallbladder and liver, and possibly other cancers. It has been estimated that 15-20% of all cancer deaths in the United States can be attributed to overweight and obesity. At present, the strongest empirical support for mechanisms to link obesity and cancer risk involves the metabolic and endocrine effects of obesity, and the alterations that they induce in the production of peptide and steroid hormones. As the worldwide obesity epidemic has shown no signs of abating, insight into the mechanisms by which obesity contributes to tumour formation and progression is urgently needed, as are new approaches to intervene in this process.