Twenty-year follow-up data from over 14,000 individuals indicate that daily doses of 75 mg or more of aspirin taken for five or more years reduces the long-term incidence and mortality of colorectal cancer. These findings were recently published in the journal The Lancet.
Some studies have suggested that use of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen may help protect against colorectal cancer. These studies, however, haven’t determined the lowest possible effective dose for colorectal cancer prevention or how long aspirin or other NSAIDs must be used to have a protective effect. In a recent study published in the journal Gut, researchers concluded that this low dose of aspirin—75 mg per day—may help protect against colorectal cancer, that aspirin must be taken regularly for one year before the effect is apparent, and that protection increases for up to 10 years. 
The current study evaluated patient data from four randomized trials in order to determine the preventive effect of aspirin on colorectal cancer over 20 years. Patients enrolled in these trials were randomized to either receive aspirin or not to receive aspirin. Average duration of scheduled treatment was six years. Death certificate and cancer registry data from over 14,000 patients were analyzed to determine colorectal cancer incidence and mortality in addition to assessing the effects of aspirin dose and duration of treatment.
The researchers concluded that 75 mg daily (or more) of aspirin taken for five years or more reduced the long-term risk of developing and dying from colorectal cancer. Individuals may wish to speak with their physician regarding the risks and benefits of daily aspirin use for reducing the risk of colorectal cancer.
 Din FV, Theodoratou E, Farrington SM, et al. Effect of aspirin and NSAIDs on risk and survival from colorectal cancer. Gut [early online publication]. September 15, 2010.