NEW YORK (Reuters Health) - Obese women who have not yet experienced menopause are twice as likely to develop colorectal cancer as slimmer women of the same age, researchers reported in a study released Thursday.

However, obesity does not appear to be associated with a higher risk of colorectal cancer in women who have gone through menopause, according to Dr. Paul Terry of the Albert Einstein College of Medicine in the Bronx, New York, and his colleagues.

Previous studies have consistently found that obesity increases the risk of colorectal cancer in men, but could find no clear evidence of this association in women.

That may be because earlier studies did not factor in the effect of menopause on the risk of colorectal cancer in obese women, Terry and his colleagues note.

Although the study did not examine whether losing weight helps reduce cancer risk in young, obese women, these results indicate that women who are overweight may now have an added incentive to drop some pounds.

"It stands to reason that losing weight--especially through good diet and exercise--is a means by which young women who are overweight or obese can prevent colon cancer," Terry told Reuters Health.

During the study, Terry's team reviewed data collected as part of a breast cancer study that included nearly 90,000 women aged 40 to 59, who were followed for an average of 10.5 years.

Over the course of the follow-up period, 527 women developed colorectal cancer. Taking obesity into account, the investigators discovered that obese women who had not yet undergone menopause were almost twice as likely to develop the disease as their slimmer, similarly-aged peers. Obesity appeared to have no effect on colorectal cancer risk in women who had experienced menopause, the authors note in the August issue of the journal Gut.

People who are obese have higher-than-average levels of insulin circulating in their blood. In an interview with Reuters Health, Terry explained that insulin can lead to high levels of a substance known as free insulin-like growth factor-1 (IGF-1), which previous studies have linked to an increased risk of colorectal cancer in both sexes.

After menopause, the risk of colorectal cancer was no higher, and possibly lower, in obese women compared to thinner women. It's possible that estrogen produced by fat cells may help ward of cancer risk in obese women after menopause. The female hormone is known to be protective when it comes to colorectal cancer.

"Given the relatively high incidence of colorectal cancer in Western populations, and the rising prevalence of obesity, especially in younger age groups, the possible benefits with respect to this disease should be added to the list of potential advantages of weight control," Terry and his colleagues conclude.

SOURCE: Gut 2002;51:191-194.

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