Valued for stroke and heart attack prevention, aspirin is also recommended for colorectal cancer prevention. A Harvard study revealed regular aspirin use reduces the risk for colorectal cancer in older age by 20% if started by the age of 65. Results were based on a cohort of nearly 94,000 people followed for three decades. Participants took either 325 or 81 mg of aspirin at least twice a week.
Colorectal cancer is the second leading cause of cancer deaths in the United States. While the incidence of colorectal cancer in older adults has slowed since the 2000s, most likely due to increased screenings, it's increased since the mid-1980s and 90s in younger adults in the 20- to 54-year-old age group. This may be due in part to a more sedentary lifestyle and poor dietary habits, but other unknown variables are likely also at play. Symptoms of colorectal cancer include a change in bowel habits, diarrhea, constipation, bloody stools, abdominal pain, and unexplained weight loss. Symptoms may not be apparent until the cancer has progressed.
Aspirin is derived from willow tree bark. Willow tree bark has been used for thousands of years, including by Hippocrates, for pain management and fever. Aspirin is thought to decrease colorectal cancer risk by modifying activity of the enzyme cyclooxygenase-2 (COX-2). Increased activity of COX-2 has been consistently found in patients with colorectal cancer. COX-2 is involved in the production of pro-inflammatory compounds known as prostaglandins that promote cell proliferation and resistance to apoptosis.
The most common side effects of aspirin include gastrointestinal upset that can include gastrointestinal bleeding, so it should be avoided by people with peptic ulcer disease. Aspirin is more likely to cause allergic reactions in people with asthma or chronic rhinosinusitis.
This study highlights the potential importance of an inexpensive and widely available intervention in preventing and further slowing the rate of colorectal cancers. Researchers, however, cautioned that the study is observational and doesn't actually prove that aspirin prevents colorectal cancer.
Sources: Harvard Health Publishing, StatPearls, Nat Rev Cancer, CDC, American Cancer Society