TOKYO (Reuters) - Drinking three or more cups of coffee a day may cut the risk of  colon cancer in women by half, according to a study by Japanese scientists.

Researchers from Tokyo's National Cancer Center studied data from more than 96,000 men and women aged between 40-69 over a period of up to 12 years from 1990, a member of the team said on Wednesday. They found no significant benefit in men.

Even after adjusting for other factors including diet and exercise, they found that women who drank three or more cups of coffee a day had half the risk of developing colon cancer, compared with those who drank no coffee at all.

The researchers, whose findings have been published in the International Journal of Cancer, did not find any link between consumption of green tea and colon cancer.

"In Japan, almost all the male population drinks alcohol and there are a large number of smokers," said Manami Inoue of the research team. "There may be some benefit from coffee for men, but it may be that we were unable to adjust for these factors."

The mechanism by which coffee may prevent cancer is unknown, Inoue said. The caffeine it contains could stimulate the working of the colon, or the effect could be due to coffee's antioxidant properties, she said.

"Some people cannot tolerate caffeine, so they should not force themselves to drink coffee. But for people who like it, there is no reason to give it up," Inoue said.