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Premenopausal Obesity Doubles Colorectal Cancer Risk
Gut
07/18/2002
By Harvey McConnell
Obesity among premenopausal women may increase their risk of developing colorectal cancer.
Previous research has identified a risk in men, but has not pinpointed the same level of risk in women, point out Dr Peter Terry and colleagues at the Albert Einstein College of Medicine, New York. They assessed risks for obese premenopausal women who were among 89,835 women who were aged between 40 and 59 at recruitment into the Canadian National Breast Screening Study.
The Canadian study was a multicentre randomized controlled trial of mammography screening for breast cancer. During an average 10.6 years of follow-up (936 433 person years), a total of 527 women were diagnosed with incident colorectal cancer: 363 colon and 164 rectal.
When the researchers set these findings against weight, they found that premenopausal women who were clinically obese, defined as a body mass index of 30 kg/mē or more, were twice as likely to develop the disease.
Women who became very overweight after the menopause did not have an increased bowel cancer risk, and if anything, it was slightly decreased.
The clinicians said earlier studies have raised the possibility that a high relative body weight may be associated with an increased risk of colorectal cancer through the mitogenic effects of increased blood levels of insulin.
They suggest it appears from their study that excess body fat is associated with increased levels of blood insulin and insulin like growth factors. An increase in blood insulin levels lowers insulin-like growth factor (IGF) binding protein 1 and may subsequently lead to increased levels of free IGF-1, which has been positively associated with the risk of colorectal cancer in men and women.
Among postmenopausal women, the clinicians add, fat tissue is an important source of oestrogen, which may be protective and counteract the harmful effects of insulin. By contrast, fat tissue is a negligible source of total circulating oestrogen before the menopause, and women who very overweight in youth and young adulthood may increase their risk of colorectal cancer.
GUT 2002; 51:191-4.
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