SUNDAY, May 8 (HealthDay News) -- Even a little exercise may ward off polyps in the colon, which are sometimes precursors to cancer.

In fact, just an hour a week of low-intensity exercise -- even such seemingly trivial activities as walking on the street or climbing stairs -- reduced risk, especially among individuals who are obese or overweight, according to new research slated to be presented Sunday at Digestive Disease Week in Chicago.

The New York City researchers noted that benefits were seen across a variety of ethnic groups and weight ranges.

The findings are not really new, just confirmatory of what doctors have been urging all along: get out and move, not just to prevent polyps but to prevent a whole host of diseases.

"Exercise is a good thing," said Dr. David Weinberg, chairman of medicine at Fox Chase Cancer Center in Philadelphia. "It matters in sick people and black people and skinny people and overweight people."

Although many previous studies have been done on this subject, not many looked at the effect of exercise in a multi-ethnic group.

"African-Americans are disproportionately impacted by colon cancer. Even within our own sample, blacks had the highest prevalence of polyps and adenomas [benign tumors that can become cancerous]," said study author Dr. Nelson Sanchez, attending physician at Memorial Sloan-Kettering Cancer Center in New York City. "Overweight and obese people are another segment of the population that is at increased risk of colon cancer and colon polyps."

This study included almost 1,000 patients of different ethnic and racial groups: 56.8 were Hispanic, 20.6 percent were Asian, 15.2 percent were black and 7 percent were white. The participants were middle-aged and at no increased risk for colon cancer or polyps. About two-thirds were overweight and about half exercised for at least an hour a week.

After performing screening colonoscopies, the researchers determined that people who exercised one or more hours a week had a 25.3 percent risk of polyps, versus 33.2 percent for those who didn't meet this exercise threshold.

The hour of weekly exercise lowered the risk of adenomas in people who were overweight and who were black. The risk of cancer was also lowered in black study participants.

Also, "individuals who exercised for at least three years had increased protection from colon polyps," said Sanchez, who spoke at an April 21 news conference on the research.

"Nobody knows why there's a benefit from exercise," Weinberg said. "You can come up with a couple of reasonable hypotheses. Is it because you're altering some important set of biological pathways? There's a lot of data that link obesity and polyps. Does that operate through insulin and insulin growth factors?"

The findings, added Sanchez, "have a great public health impact."

Now the job is to determine exactly which exercises are the most beneficial, he said.

Because the study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

The U.S. National Cancer Institute has more on colon cancer.