Obesity related to more than 100,000 cancer cases a year

By Sheilah Downey

In addition to being a risk factor for many diseases including diabetes and H1N1 swine flu, obesity is said to be the cause of more than 100,000 cancer cases each year in the United States, according to a new estimates.

A report by the American Institute for Cancer Research estimated that the occurrence of many cancers, including more than 33,000 breast cancers,   could be attributed to poor diet, lack of physical activity and excess body fat.

Although not as deadly as smoking -- according to studies -- obesity has a three-fold affect on seven types of cancer, according to the study by the AICR.

And with obesity numbers continuing to spiral, about 60 million Americans are said to be obese according to the Centers for Disease Control, the estimates could be cause for concern.

"We now know that carrying excess body fat plays a central role in many of the most common cancers," said Dr. Laurence N. Kolonel, deputy director of the Cancer Research Center of Hawaii and a member of the reporting panel.

"And it's clearer than ever that obesity's impact is felt before, during and after cancer -- it increases risk, makes treatment more difficult and shortens survival."

Dr. Kolonel said emerging evidence has revealed a convincing link between obesity and cancers of the esophagus, pancreas, kidney, breast and colorectum.  The link between obesity and gall bladder cancer was thought to be probable, according to the report.

How is obesity able to create cancers in so many systems of the body? Researchers said that excess body fat increases the level of sex steroids and other hormones that have been linked to cancer growth. Fat tissue is known to produce estrogen, which has been shown to promote cell proliferation in breast cancer.

Other studies have suggested that excess body fat lowers immune function and increases oxidative stress which can lead to DNA damage.

Obesity and cancer survivorship

Even after successful cancer treatment, obesity negatively affects survival rates for the patient, according to findings from Dr. Melinda Irwin, Associate Professor of Epidemiology at Yale University.

Dr. Irwin said that data indicates that a higher body mass index (BMI) has been linked to poorer survival rates.

"It's true that higher BMI is associated with poorer outcomes," said Dr. Irwin. "An increasing number of studies suggest that regular physical activity improves cancer survival, even among survivors who are overweight or obese. That's really the take-home message here."

In a review of past studies, Dr. Irwin said that by increasing physical activity after a cancer diagnosis, especially among those who were inactive before, raises chances of survival.

Regular physical activity helps regulate hormone levels and studies have shown that women with higher insulin levels have a three-fold risk of death when compared to women with low insulin levels, Dr. Irwin said.

In studies done by Irwin at her Yale Exercise and Survivorship (YES) Study trial, findings revealed that regular exercise decreased insulin levels by about 8 percent among 933 breast cancer survivors.