Taking aspirin as infrequently as 1 to 3 times a month reduced the risk of all-cause and cancer-related mortality in older adults in the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial compared to no aspirin use, a post-hoc analysis of 146,152 individuals in the trial indicated.

Moreover, more frequent, weekly use of aspirin significantly reduced the risk of mortality from both gastrointestinal and colorectal cancer and it reduced all mortality endpoints regardless of body mass index (BMI), Holli Loomans-Kropp, PhD, MPH, National Cancer Institute, Rockville, Maryland, and colleagues reported in JAMA Network Open.

The analysis was based on participants' self-reports of aspirin use in the previous year, collected at enrollment.

At a median follow-up of 12.5 years (range 8.7-16.4 years), the risk of all-cause mortality was reduced by 16% (HR 0.84, 95% CI 0.80-0.88, P<0.001) among those who took aspirin 1 to 3 times a month versus none.

Taking aspirin once or twice weekly reduced the same endpoint (HR 0.86, 95% CI 0.81-0.90, P<0.001). Similar risk reduction for all-cause was also seen when aspirin was taken 3 or more times per week (HR 0.81, 95% CI 0.80-0.83, P<0.001).

Cancer mortality was also reduced with aspirin use 1 to 3 times per month (HR 0.87, 95% CI 0.81-0.94, P<0.001); more frequent use was also associated with reduced cancer mortality though the magnitude did not increase markedly (HR 0.85 for use 3 times or more per week, 95% CI 0.81-0.88, P<0.001).

Risk reductions were seen as well with frequent aspirin use for gastrointestinal cancer mortality (HR 0.75, 95% CI 0.66-0.84, P<0.001) and colorectal cancer mortality (HR 0.71, 95% CI 0.76-0.89, P<0.001).

When participants were stratified by baseline BMI, every mortality endpoint was also significantly reduced with aspirin use irrespective of weight status, and with no suggestion that the apparent protective effect was diminished for overweight/obese individuals.

"These findings suggest that prophylactic aspirin use may reduce risk of mortality among older individuals," the authors concluded.

The PLCO Cancer Screening Trial randomized participants ages 55-74 to cancer screening or to a control arm at 10 centers in the U.S. This particular analysis included those participants who were 65 or older at baseline or survived to age 65 during follow-up. Mean participant age at baseline was 66.3 and slightly over half were women.

Loomans-Kropp and colleagues pointed out that evidence regarding the prophylactic benefit of aspirin in older adults has been mixed.

For example, the Aspirin in Reducing Events in the Elderly (ASPREE) study found that during 4.7 years of follow-up, adults from ages 65 to 70 years who took 100 mg of aspirin a day were at increased risk for all-cause mortality compared to placebo controls. However, this study contradicted many others that supported a survival benefit with aspirin. Loomans-Kropp and colleagues thus wanted to revisit the question and also to explore whether aspirin might be less protective among individuals who were overweight or obese.

The U.S. Preventive Services Task Force currently recommends low-dose aspirin for the prevention of both cardiovascular disease and colorectal cancer among individuals from ages 50 to 59 at average risk for cardiovascular disease, although they suggest treatment should be individualized for those from ages 60 to 69. The USPSTF made no recommendations for aspirin use in individuals 70 years of age and older, citing insufficient evidence.