A common anti-inflammatory drug, widely used for many purposes from reducing fevers to acting as a blood thinner for preventing heart attacks, has now been found to have an unexpected benefit: reducing the risk of colorectal cancer.

Researchers have found that regular use of aspirin could slash colorectal cancer risk in people already at risk from unhealthy lifestyles.

Colorectal cancer, a leading cause of cancer-related deaths in the U.S., is on the rise among young adults. This type of cancer occurs when malignant cells affect the tissues of the colon or rectum. Many factors, including changes in genetic material and a generally unhealthy lifestyle, such as lack of physical activity, a low-fiber and high-fat diet, obesity, alcohol consumption, and tobacco use, raise the risk.

The researchers of the latest study came across the potential benefits of aspirin in colorectal cancer prevention after examining the health data from 107,655 participants of the Nurses' Health Study and Health Professionals Follow-Up Study.

The team estimated the colorectal cancer rates in those who took aspirin regularly and compared it with those who did not. By regular use, the researchers mean either two or more standard dose (325 mg) tablets per week or daily intake of low-dose (81 mg) aspirin.

After follow-up for more than three decades, the researchers noticed that the 10-year cumulative incidence of colorectal cancer was 1.98% in regular users of aspirin and 2.95% in those who did not use aspirin. The results were published in Jama Network Open.

The researchers observed the maximum benefits of aspirin use among those with the unhealthiest lifestyles. In this group, the risk of getting colorectal cancer was 3.4% without the regular use of aspirin and 2.12% with the regular use.

The difference was less pronounced when researchers compared the aspirin use among those with the highest healthy lifestyle scores, where colorectal cancer rates were 1.5% in regular aspirin users and 1.6% in those without aspirin use.

The researchers then concluded that if 78 patients in the unhealthiest group were treated with aspirin, it could prevent one case of colorectal cancer over a 10-year period. In contrast, among the healthiest group, treating 909 patients with aspirin could prevent one case of colorectal cancer.

"We sought to identify individuals who are more likely to benefit from aspirin to facilitate more personalized prevention strategies," co-senior author Andrew Chan said in a news release.

"Our results show that aspirin can proportionally lower the markedly elevated risk in those with multiple risk factors for colorectal cancer. In contrast, those with a healthier lifestyle have a lower baseline risk of colorectal cancer, and, therefore, their benefit from aspirin was still evident, albeit less pronounced," said Dr. Daniel Sikavi, lead author of the paper.

The researchers caution that the study is observational and has not estimated the potential side effects of daily aspirin use, such as bleeding.

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