Tom Murphy
RedwoodAge.com

Just in case you needed one, here's another reason to watch your weight: those who develop colon cancer while obese are much more likely to die from it, according to a study at the Mayo Clinic.

Depending on gender and various levels of body fat, the risk of dying from the disease rose by 19 to 35 percent compared to other patients.

It's long been known that overweight people are more likely to get colon cancer. This study is the first to show that once someone gets it, their body mass index - a ratio of height to weight - will influence the likelihood they'll die from it. A number of web sites can help people determine their BMI.

The study, which was supported by the National Cancer Institute and published in the journal Clinical Cancer Research, suggests colon cancer patients should try to maintain a body mass index less than 30, which includes those who are merely "overweight" with a BMI of 25-29.9.  

"We found that obesity is associated with more aggressive colon cancers, with the effect being stronger in men than in women," said Dr. Frank Sinicrope, an oncologist who led the study. "Our data suggest that a little extra weight is okay, but body weight in the obesity range puts a patient at increased risk for cancer recurrence and spread and, based upon other studies, also would be expected to increase the risk of precancerous colon polyps and a second colon cancer."

The study included 4,381 patients in a number of separate clinical trials. Of those, 20 percent (868) were obese based on their BMI. Of those 606 had a BMI of 30-34.9 and 262 were "very obese" with a BMI of 35 or more.

Any class of obesity showed a significant connection to increased number of cancerous lymph nodes, and the very obese showed a 19 percent increased risk of death.

Higher in Men
"The greater the level of obesity in men, the higher their risk of cancer recurrence and death," said Sinicrope. The very obese men had a 35 percent increased risk of death compared to men of normal weight. 

"In women, however, the highest risk was seen in those with class 1 obesity, compared to normal weight women," he said. That is, the very obese women had only an 11 percent increase risk of death. But women with a BMI of 30-34.9 had a 24 percent increased risk.

Because of estrogen levels, menopause and hormone therapies, the study of women is more complicated than men.

The study also found interesting patterns among people who weren't obese. For men, those were were overweight but not obese had a 6 percent improvement in survival. And underweight women had worse survival rates - confirming a finding from prior studies.

The link between obesity and the more aggressive cancers remain murky, but researchers know that hormones such as insulin and growth-factor-1 are found both in obese people and in colon cancer patients. 

"The association between body weight and increased risk of cancer recurrence and death is obviously complicated, and we need further studies to help clarify this relationship, but such information has the potential to help patients survive their cancer and assist physicians in caring for them," Sinicrope said.