A careful scientific review of obesity and cancer finds that obesity seems to cause certain cancers. This a wake-up call to anyone who is deeply overweight and needs a reason to see your doctor and change your habits.
Colon, endometrial and post menopausal breast, probably because of hormonal changes; adenocarcinoma of the esophagus, especially in men, probably because of acid heartburn and local inflammation; and cancers of the liver, gallbladder and pancreas, possibly related to hyperinsulinemia and insulin resistance.
� Obese postmenopausal women are 50% more likely to develop breast cancer than normal-weight women.
� Obese men are twice as likely to develop colorectal cancer as normal-weight men.
� Obese women are as much as 3.5 times as likely to develop endometrial cancer than women of normal weight.
Read more below.
Nature Reviews Cancer 4, 579 -591 (2004); doi:10.1038/nrc1408
OVERWEIGHT, OBESITY AND CANCER: EPIDEMIOLOGICAL EVIDENCE AND PROPOSED MECHANISMS
Eugenia E. Calle & Rudolf Kaaks about the authors
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.
The International Agency for Research on Cancer has determined that, based on results from epidemiological studies, people who are overweight or obese are at increased risk of developing several cancer types, including adenocarcinoma of the oesophagus, colon cancer, breast cancer (in postmenopausal women), endometrial cancer and kidney (renal-cell) cancer.
Epidemiological evidence also indicates that cancers of the liver, gallbladder and pancreas are obesity related, and that obesity might also increase risk for haematopoietic cancers and for aggressive prostate cancer. No association is seen between obesity and lung cancer. Results for other cancers have been inconsistent.
Insulin resistance develops as a metabolic adaptation to increased levels of circulating free fatty acids released from adipose tissue, especially intra-abdominal adipose. Insulin resistance is generally compensated by increased pancreatic insulin secretion. There is mounting epidemiological and experimental evidence to indicate that chronic hyperinsulinaemia increases risk of cancers of the colon and endometrium, and probably other tumours (for example, of the pancreas and kidney).
Serum levels of insulin-like growth factor 1 (IGF1) are also associated with different forms of cancer. However, there is no simple, direct relationship between circulating levels of IGF1 and the degree of adiposity.
Circulating levels of oestrogens are strongly related to adiposity. For cancers of the breast (in postmenopausal women) and endometrium, the effects of overweight and obesity on cancer risk are largely mediated by increased oestrogen levels.
In 4�8% of premenopausal women, obesity and ensuing insulin resistance can either cause or aggravate syndromes of ovarian androgen excess (polycystic ovary syndrome) and chronic progesterone deficiency. There is strong evidence that such syndromes, along with reduced progesterone production, increase the risk of endometrial cancer.
Successful intervention strategies for weight loss and maintenance at the individual and community level are needed to reduce cancer risk.
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