Further, he added, "bicycling and walking are great ways to incorporate regular exercise into a hectic schedule."

Several Western researchers have found that low physical activity increases the risk of various cancers, colon cancer in particular, but few such studies have been conducted in Asia.

Over the past 20 years, colon cancer has been on the rise in Shanghai, China, where the risk used to be low compared with a formerly low-risk country relative to other countries. But China has become increasingly Westernized in terms of its transportation and dietary practices.

Until the early 1990s, most residents commuted by cycling, or a combination of walking and riding the bus, and rarely participated in leisure-time physical activity.

To assess the impact of commuting physical activity on colon cancer risk, Hou and his team studied 931 colon cancer patients and 1,552 comparison individuals. The study participants were all 30 to 74-year old residents of urban Shanghai.

On average, the participants reported high levels of commuting physical activity, with the lowest level corresponding to about seven weekly hours of jogging or tennis, Hou and his team note.

Men and women with high levels of such activity had a 50 percent reduced risk of colon cancer, they report in the American Journal of Epidemiology.

Long-time exercisers, who maintained consistently high physical activity levels for at least 35 years were up to 69 percent less likely to be diagnosed with the condition.

With regard to the specific commuting activity and the amount of time spent in the commute, the researchers found that people who bicycled more than two hours each day had a nearly 59 percent lower risk of colon cancer, and those who walked more than a half hour each day had a 43 percent reduced risk.

In other findings, colon cancer risk increased as physical activity decreased, particularly among men and women with a higher body mass index, a measure of weight in relation to one's height.

"This finding is important because it shows low physical inactivity is a major risk factor for colon cancer even for a population with relatively low rates for this cancer," Hou said.

How physical activity decreases colon cancer risk is still unclear. Researchers speculate that it may involve "a set of complex mechanisms" including shortened bowel transit time due to the movement of the colon and enhanced immune system function resulting from the exercise, the report indicates.

What is clear, however, is the applicability of the findings to residents of the U.S. and other countries, according to Hou.

"We expect to see the same or even greater beneficial effect of incorporating walking and bicycling into our daily commute in the U.S., since the portion of the U.S. population who commute by cycling and walking is relatively small," he said.

Since an estimated 64 percent of American adults are either overweight or obese, Hou said, "physical activity may be an important method of cancer prevention in the U.S."

What's more, "commuting by bicycle and walking may not only reduce the health burden of the nation, but has the added benefits to the community of reducing traffic and pollution," he added.