THURSDAY, Oct. 21 (HealthDay News) -- People who regularly take a low dose of aspirin may be reducing their risk of developing colon cancer by 24 percent, a new study finds.

Moreover, for those who take low-dose aspirin (about 75 milligrams/day) but do develop the disease, their risk of dying from it could be cut by more than a third, the researchers added.

For the study's lead author, at least, the data offers strong support for aspirin's cancer-fighting potential.

"This is proof that low-dose aspirin prevents colorectal cancer," said Dr. Peter Rothwell, a professor of neurology at John Radcliffe Hospital and the University of Oxford in the UK.

"Somewhat fortuitously, it mainly prevents those cancers that are least well-prevented by screening colonoscopy," he said.

Patients at increased risk of colorectal cancer, such as those with a family history of previous polyps, should take low-dose aspirin long-term, Rothwell believes.

"This additional cancer benefit of aspirin helps to tip the balance of risk and benefit in favor of healthy individuals who chose to take low-dose aspirin," he added.

The report is published in the Oct. 21 online edition of The Lancet.

For the study, Rothwell's team reviewed data from four randomized trials -- evaluating the ability of aspirin to prevent vascular disease and to determine aspirin's effect on colorectal cancer.

The four trials included more than 14,000 people who were treated with aspirin or placebo for an average of six years. During an average of 18 years of follow-up, 2.8 percent developed colorectal cancer, the researchers found.

Pooling the data from all the trials, Rothwell's group calculated that taking low-dose aspirin reduced the 20-year risk of developing colorectal cancer by 24 percent.

In addition, for those taking aspirin who developed colorectal cancer, the risk of dying from the condition was reduced by 35 percent.

These effects were consistent across the trials and at a dose of aspirin of 75 milligrams a day. Higher doses of aspirin did not appear to add any benefit, the researchers noted.

The researchers also found a reduction in the 20-year absolute risk of any fatal colorectal cancer after five years among those taking 75 milligrams to 300 milligrams of aspirin daily. The risk went from about 3.5 percent among those taking a placebo to 1.5 percent for those taking aspirin, the data showed.

Seventy percent of reductions seen in colorectal cases and deaths were due to fewer cancers in the right part of the colon called the proximal colon, but the aspirin effect did not seem to reduce cancer in the lower part of the colon called the distal colon, and had only a small effect on rectal cancer, the researchers noted.

Most colorectal cancers develop from polyps and screening sigmoidoscopy and colonoscopy can reduce the risk by removal of these polyps. However screening is not 100 percent effective, particularly for cancers in the proximal colon, they added.

Dr. Robert Benamouzig, from the Department of Gastroenterology at Avicenne Hospital in Bobigny, France, and author of an accompanying journal editorial, said people at normal risk for colorectal cancer should not start taking aspirin to prevent colorectal cancer.

"But if you are at high risk then, yes, you should take low-dose aspirin," he said. "Right now, the evidence seems strong for high-risk people, but not for average-risk people."

How aspirin might work to reduce the risk of colorectal cancer is not fully known, but it may be due to aspirin's ability to reduce inflammation, Benamouzig said.

The downside of daily doses of aspirin is the potential risk of gastrointestinal bleeding. So, before starting a regimen of aspirin you should consult with your doctor, experts say.

More information

For more information on colon cancer, visit the U.S. National Cancer Institute.