Aspirin—it’s so inexpensive, so common, and so familiar that it would seem incapable of anything new or surprising. But much of what is known about aspirin still needs to be quantified. For example, daily aspirin has been known to protect against cancers of the digestive tract. It also has been known to increase the risk of bleeding, particularly gastrointestinal bleeding and peptic ulcer. But these bits of knowledge about long-term aspirin use have done little to clarify a key point: Do the potential benefits of daily aspirin outweigh the potential harms?
To put numbers to the question—and hopefully settle it—scientists from Queen Mary University of London (QMUL) reviewed all the available evidence from many studies and clinical trials. These researchers, led by Professor Jack Cuzick, the head of QMUL’s Centre for Cancer Prevention, found that taking aspirin for 10 years could cut bowel cancer cases by around 35% and deaths by 40%. Rates of esophageal and stomach cancers were cut by 30% and deaths from these cancers by 35–50%.
In addition to collating data about aspirin’s cancer-prevention abilities, the researchers sifted through Medline data regarding harmful effects of aspirin and baseline rates of harms such as gastrointestinal bleeding and peptic ulcer. The researchers found that in general, the risk and fatality rate associated with bleeding increases with age.
Among 60-year-old individuals who take daily aspirin for 10 years, the risk of digestive tract bleeds increases from 2.2 to 3.6%, and this could be life-threatening in a very small proportion (less than 5%) of people. Overall, rates of serious or fatal gastrointestinal bleeding are very low under the age of 70, but increase sharply after that age. Another side effect of aspirin use is peptic ulcer, the risk of which is increased by 30–60%.
These results appeared August 5 in the journal Annals of Oncology, in an article entitled, “Estimates of benefits and harms of prophylactic use of aspirin in the general population.” Besides weighing the anticancer benefits against digestive-bleed harms, the article offered a “best estimate” for the overall benefits and harms of aspirin prophylaxis in the general population.
For individuals taking aspirin for 10 years, the authors indicated, there would be a “relative” reduction of about 9% in the number of men and 7% in the number of women with a cancer, myocardial infarction, or stroke event over a 15-year period. They also found an overall 4% relative reduction in all deaths over a 20-year period. The authors cautioned that “absolute” reductions are age and sex dependent.
The study also uncovered uncertainty over the most appropriate dose of aspirin required to maximize the benefit/harm ratio, with doses varying between 75 and 325 mg a day in different clinical trials and studies. It was also unclear whether taking aspirin for longer than 10 years would result in greater benefits.
“While there are some serious side effects that can’t be ignored, taking aspirin daily looks to be the most important thing we can do to reduce cancer after stopping smoking and reducing obesity, and will probably be much easier to implement,” commented Professor Cuzick. “The benefits of aspirin use would be most visible in the reduction in deaths due to cancer.”
In the Annals of Oncology article, Professor Cuzick and colleagues concluded that “prophylactic aspirin use for a minimum of five years at doses between 75 and 325 mg/day appears to have favorable benefit–harm profile” and that “longer use is likely to have greater benefits.” Further research, they explained, is needed to “determine the optimum dose and duration of use, to identify individuals at increased risk of bleeding, and to test effectiveness of Helicobacter pylori screening–eradication before starting aspirin prophylaxis.”