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Women past menopause who are obese and diagnosed with colon cancer appear to face a greater risk of dying from all causes than those who are at a healthy weight or merely overweight, a new study shows.
And trying to lose weight after the diagnosis may be too late, researchers cautioned. Abdominal obesity even prior to the diagnosis of colon cancer was associated with an increased risk of dying after contracting the disease, according to study author Anna Prizment, a postdoctoral fellow at the University of Minnesota Masonic Cancer Center, in Minneapolis.
Body shape may play a role as well.
Women with the disease who have an unhealthy waist-to-hip ratio and a large waist are at increased risk of death, Prizment added.
Colon cancer is the second leading cause of cancer-related death among women and men combined. It is expected to kill more than 51,000 people -- including nearly 25,000 women -- in the United States in 2010, according to the American Cancer Society.
Many studies have found a link between excess body weight and a higher risk of colon cancer. "But not so many studies have examined how obesity affects survival of the colon cancer patient," Prizment said.
So, with her colleagues, she evaluated women who had participated in the Iowa Women's Health Study, focusing on 1,096 women participants who were diagnosed with colon cancer between 1986 and 2005. Body and weight measurements were obtained before the colon cancer diagnosis.
The study was retrospective, meaning that the data used had been recorded for reasons other than research.
During the follow-up period of up to 20 years, 493 women died. Among this group, colon cancer was the underlying cause in 289 deaths.
Obese women -- those with a body-mass index (BMI) of 30 or higher -- had a 45% increase in all causes of death compared to women with a healthy weight, according to Prizment. Their risk of dying from colon cancer also climbed by 32% compared to healthy weight women, but that finding was not significant from a statistical point of view. However, the 45% increase in all causes of death was clinically significant.
The researcher also found that the risk of dying was higher among underweight women, those with a BMI below 18.5. "But we don't want to talk much about them because we had too few of them," Prizment said.
Prizment expanded on the unhealthy waist-to-hip ratio and large waist associations that she found were associated with a higher risk of dying from colon cancer.
A waist-to-hip ratio of 0.80 or below for women is considered low-risk. For instance, a woman with a waist of 27 inches and hips of 36 inches has a waist-to-hip ratio of .75.
Women with waists of 37.5 inches or higher had a higher death risk than those with a healthier waist size, she found.
Exactly why the obese women with unhealthy waist-to-hip ratios and big waists are at increased risk of death from colon cancer compared to slimmer women isn't known. "They may be diagnosed at an advanced stage," Prizment said. "They may have less access to health care. There could be a direct biological mechanism."
Her advice for women? "Maintain a healthy body weight is the only recommendation we can give for all postmenopausal women," she said.
Until the new study, findings about excess body size in colon cancer patients and risk of death have been mixed and conflicting, said Dr. Peter Campbell, director of the tumor repository for the American Cancer Society.
One strength of the new study, he said, is that "body size was measured before they had the diagnosis." Measuring after diagnosis may not give a true picture, he said, as weight loss can occur after the diagnosis.
"It's lifelong body size that's important [to know in gauging risk]," he said. "This study adds important new information to our understanding of body size and health."
He agreed with Prizment that the finding underscores the importance of maintaining a healthy body weight with age.
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