Regular aspirin use is linked to a reduced risk of colorectal cancer, but this benefit is most pronounced among adults who maintain healthy lifestyle habits, regardless of their aspirin consumption.

According to recent findings, individuals who take aspirin regularly exhibit a lower incidence of colorectal cancer compared to non-users. The effect is particularly significant for those with less healthy lifestyles, such as moderate or heavy smokers and those with overweight or obesity.

In 2024, the U.S. based study shows that an approximate 152,810 people in the U.S. are expected to be diagnosed with colorectal cancer, with over 53,000 anticipated fatalities, as reported by the National Cancer Institute of the U.S.. Although the overall rates of colorectal cancer have declined by about 1% annually from 2011 to 2019, this trend predominantly applies to older adults. In contrast, rates among individuals under 55 have seen an increase of 1% to 2% since the mid-1990s.

Genetics undeniably influence the development of colorectal cancer. Those with a parent, sibling, or child who has had colorectal cancer face a heightened risk. Nonetheless, lifestyle factors such as obesity, type 2 diabetes, an unhealthy diet, smoking, and alcohol consumption can also elevate the risk.

Researchers from Massachusetts General Hospital and Harvard Medical School have discovered that regular aspirin use may mitigate colorectal cancer risk in individuals leading unhealthy lifestyles. Their study, published in JAMA Oncology on August 1, reveals that regular aspirin consumption can lower the risk of colorectal cancer. In 2016, the US Preventive Services Task Force (USPSTF) recommended low-dose aspirin for adults aged 50 to 59 to prevent colorectal cancer. However, this recommendation was withdrawn in 2022 due to insufficient evidence supporting aspirin’s ability to reduce the likelihood of developing or dying from colorectal cancer. Additionally, long-term aspirin use can lead to gastrointestinal bleeding, ulcers, and other complications.

Motivated by prior research indicating aspirin’s potential to reduce colorectal cancer risk, the authors of the new study explored whether this benefit was more pronounced in individuals with specific lifestyle factors. The study examined data from over 107,000 participants in the Nurses’ Health Study and the Health Professionals Follow-up Study. The average age of participants was 49 years, and they were all health professionals, with a majority being white. Further research is needed to determine if these results hold true across more diverse populations.

Participants were followed for over three decades and completed surveys on five lifestyle factors: body mass index (BMI), tobacco and alcohol use, physical activity, and diet. They also reported their aspirin or other medication use and any diseases they developed during the study period, including colorectal cancer. Regular aspirin use was defined as two or more standard-dose tablets per week or six or more low-dose tablets per week.

The study found that the 10-year risk of developing colorectal cancer was 1.98% among regular aspirin users compared to 2.95% for non-users. Regular aspirin users had an 18% lower relative risk of being diagnosed with colorectal cancer than non-users or infrequent users.

Notably, participants with unhealthier lifestyles reaped the most significant benefits from regular aspirin use in terms of reducing their relative risk of colorectal cancer. The greatest benefits were observed among moderate or heavy smokers and individuals with a BMI of 25 or greater. BMI serves as a screening measure for overweight or obesity, with a healthy weight for adults aged 20 and older generally falling between a BMI of 18.5 to less than 25. However, BMI may not always be reliable during pregnancy or for athletes or older adults.

The study also demonstrated that individuals with healthier lifestyles benefited from regular aspirin use but to a lesser extent. It reinforced the overall advantages of maintaining a healthy lifestyle. Those with the healthiest lifestyle – whether they used aspirin regularly or not – had a lower 10-year risk of colorectal cancer compared to regular aspirin users with the unhealthiest lifestyle.

While the study does not explain how regular aspirin use might help prevent colorectal cancer, previous research suggests that aspirin may inhibit pro-inflammatory signals contributing to cancer growth. Given the risks associated with long-term aspirin use, such as gastrointestinal bleeding, the study authors recommend using lifestyle risk factors to identify individuals who might benefit more from aspirin for cancer prevention.

Several experts believe that the study’s findings could prompt a reconsideration of the USPSTF’s stance on regular aspirin use for colorectal cancer prevention. However, some experts argue that the study’s evidence is insufficient to alter existing recommendations. The study was not a randomised controlled trial (RCT) comparing aspirin users with non-users. Consequently, this level of evidence may not be robust enough to change USPSTF guidelines.

Moreover, concerns about complications like bleeding contributed to the USPSTF’s withdrawal of its recommendations for aspirin use. The new study did not provide data on how many regular aspirin users experienced bleeding or other complications. This information could impact the assessment of risks and benefits associated with regular aspirin use in individuals with unhealthy lifestyles.

The study’s implications extend beyond just aspirin use; it highlights the importance of personalised medical recommendations based on individual lifestyle factors. For instance, patients concerned about their colorectal cancer risk should consult their doctor before starting regular aspirin use.

Although aspirin is generally considered safe, some patients may be at higher risk of gastrointestinal bleeding. Therefore, no one should routinely take two large aspirins a week without medical advice. Patients should also inquire about other ways to reduce their cancer risk.

This research contributes to the growing body of evidence emphasising diet and lifestyle modifications in preventing colorectal cancer. Such changes can also lower the risk of other cancers, cardiovascular diseases, and other health issues.

While lifestyle changes are always advisable for reducing cancer risk, regular aspirin use might serve as an interim measure for those struggling to adopt healthier habits. Researchers examined data from over 107,000 health professionals who participated in long-term studies. Participants provided information on lifestyle factors and medication use. Regular aspirin users had a lower risk of being diagnosed with colorectal cancer compared to non-users. The most significant benefit was observed among those with unhealthiest lifestyles, such as smokers and individuals with overweight or obesity. Conversely, people with the healthiest lifestyles had a lower risk of colorectal cancer regardless of their aspirin use.