A comprehensive analysis of studies and trials suggests the cancer prevention benefits of a daily aspirin for at least 5 years outweigh the potential harms.
Many people already take an aspirin once a day to reduce the risk of a cardiovascular event such as a heart attack or stroke. Accumulating evidence has also suggested that aspirin could cut the risk of a cancer diagnosis or the chance of dying from commonly diagnosed cancers. However, studies and clinical trials have been mixed. Some studies have shown a marked preventive benefit of a daily aspirin (see Aspirin May Lower Risk of Pancreatic Cancer and For Some, Aspirin Cuts Colon Cancer Risk in Half). But others suggested that the potential cancer prevention benefits of aspirin don’t outweigh the risks of gastrointestinal bleeding and peptic ulcers, particularly in those who are older.
Now, the most comprehensive and up-to-date pooled analysis of research studies and clinical trials suggests that the cancer prevention benefits of a daily low-dose aspirin for at least 5 years outweigh the potential harms. The review, published in Annals of Oncology, is the largest meta-analysis yet on the over-the-counter pill’s ability to stave off disease.
The pooled analysis, led by Jack Cuzick, PhD, of the Wolfson Institute of Preventive Medicine, Queen Mary University of London in the United Kingdom, shows that individuals between the ages of 50 and 65 should consider a daily prophylactic aspirin.
The researchers’ analysis suggests that a low-dose aspirin taken every day for a decade can reduce colorectal cancers by about 35% and deaths from these cancers by 40%. Rates of stomach and esophageal cancers could be decreased by 30% and deaths from these cancers by about 35% and 50%, respectively.
“There is clear evidence for a benefit in the general population aged 50 to 65 based mostly on a reduction in cancer incidence and mortality,” Cuzick told Cancer Network. “The biggest effect is in bowel, stomach, and esophageal cancers with 30% or more reductions, and small benefits for lung, breast, and prostate cancers of about 10%. [We did not find] effects on other cancers.”
Three years of use appears to be the minimum to see any benefits; at least 5 years of use is needed to see reductions in death from cancer and 10 years are likely needed for full benefits. Long-term benefits were seen in long-time users, even after stopping the daily regimen.
The analysis showed that for those individuals of average risk who are between the ages of 50 and 65, a daily aspirin for 10 years can result in a relative decrease between 7% (for women) and 9% (for men) in the number of heart attacks, strokes, and cancer cases over a 15-year period. The overall relative reduction in death from 10 years of daily aspirin use is about 4% over a 20-year period.
Although there were no differences seen for low vs standard doses, including no excess toxicities with higher doses, none of the studies had direct comparisons.
“Increased bleeding is the most important side effect of aspirin,” said the study authors, and the most serious, potentially fatal, but rare side effect is hemorrhagic stroke. Taking aspirin every day for 10 years increases the risk of stomach bleeding from 2.2% to 3.6% among 60-year-olds. In about 5% of the cases, stomach bleeding may be fatal.
“Some people are at increased risk of bleeding, [such as those individuals ] taking blood thinning drugs like warfarin, diabetics, and those with hypertension, where aspirin is not appropriate,” said Cuzick.
Bleeding may be more common in those who have the bacterium Helicobacter pylori (H. pylori ) in their stomachs, which is a cause of peptic ulcers. H. pylori may account for about one-quarter to one-third of peptic ulcers. In those who use non-steroidal anti-inflammatory drugs, an H. pylori infection has been linked with a 2- to 3.5-fold higher risk of a peptic ulcer and a 2- to 2.5-fold higher risk of gastrointestinal bleeding. There are tests available that show whether this bacterium is present in the gut; they are recommended before considering a daily prophylactic aspirin regimen.
Still, the authors stated that more research is needed to understand the benefits of aspirin, as well as which subpopulations will derive the maximum benefit and which individuals have a higher risk of bleeding. Another outstanding question is whether a baby aspirin-less than 100 mg per day-or a standard dose of 300 mg is better. Cuzick and his coauthors also pointed out that it is unclear if there is an upper age limit at which the harms of a daily aspirin do outweigh the benefits, since bleeding risk changes with age and rates of cancer increase.