A report in the Annals of Internal Medicine, an American journal, reported that people who had taken aspirin twice or more a week over a long period were significantly less likely to develop colon or rectal cancer - among the most common and deadly forms of cancer.
The study was conducted by researchers at the Harvard Medical School and Boston's Brigham and Women's Hospital. It found that among those who had taken regular aspirin doses the longest - at least four years - the relative risk of colon or rectal cancer diagnosis was 38 per cent of that of non-aspirin users.
The study tracked 47,900 male health care professionals who have been taking part in a broader heart disease and cancer project since 1986.
Its findings provided the strongest evidence to date of the benefits of aspirin in preventing colon cancer - which have been indicated in earlier studies, the journal said in an editorial.
'With recent developments proving the efficacy of screening, ongoing advances in the identification of high-risk groups and the possibility of risk modification by diet and chemoprevention with aspirin, the prospect for decreasing mortality from colorectal cancer by preventive approaches seems bright,' the editorial said.
Its author, Dr Harinder Garewal, of the Veterans' Affairs Medical Centre in Tucson, Arizona, said one theory is that the preventive effects in aspirin may come from its impact on the production of a class of chemicals that help control the circulatory system and growth in humans.
But he said that theory has not been proven.
The editorial said cancers of the colon or rectum were among the most prevalent and lethal forms of cancer in the United States, with about 152,000 new cases and 57,000 deaths in 1993.