A new study suggests that postmenopausal women, diagnosed with cancer, have a higher mortality risk if they are underweight or overweight towards obese, before the diagnosis.

Anna E. Prizment, PhD, MPH, a postdoctoral fellow in the division of epidemiology and community health at the University of Minnesota, Masonic Cancer Center and her colleagues analyzed data from the Iowa Women's Health Study.

The study included 1,096 women diagnosed with colon cancer who were observed over a maximum 20-year period, during which 493 died, 289 from colon cancer.

Women with a BMI of at least 30 kg/m2, classified as obese, proved to have a 45 percent higher death risk that normally weight ones.

Also, the few underweight women, with a BMI less than 18.5 kg/m2, had an amazing 89 percent increased mortality rate.

Those with a very high waist-to-hip ratio increased their colon cancer related death with 30 to 40 percent, and Prizment admitted that the “exact mechanisms underlying the link between obesity and higher mortality of colon cancer patients are unknown.”

She added that “obese people may be diagnosed at later stage, have different treatment or more comorbidities,” but because abdominal obesity remained linked to colon cancer mortality even after factors like age, stage at cancer diagnosis and comorbidities were eliminated, the biological effect of obesity remains.

One explanation might be that abdominal obese women have higher hormone levels so the cancer is likely to be more aggressive.

“Maintaining a healthy body weight is beneficial for postmenopausal women [and] may also be beneficial for those diagnosed with colon cancer later in life,” said Prizment.

“It looks like abdominal obesity may be a useful indicator of higher colon cancer mortality, [but] it is too early to say whether a decrease in weight characteristics after diagnosis will also decrease mortality risk; at that point it may be too late.”

The safer solution is to simply maintain a normal and healthy body weight throughout life.

This study was published in the September issue of Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.