Volunteers who downed four cups a day saw their risk of a tumour drop by about 15 per cent.
But those who got through six or more were up to 40 per cent less likely to fall victim to the disease.
Tea lovers, however, did not see any reduction in risk, scientists said.
More than 40,000 people a year in the UK are diagnosed with bowel cancer.
The disease has a high mortality rate – around 16,000 a year – because many victims ignore early warning signs and only seek medical help once the cancer has advanced.
Diets high in fat and red meat, as well as lack of exercise, are thought to be among the main risk factors.